Date: 2026-07-30T21:14:20+00:00

Actual source code: snes.c

      1: #include <petsc/private/snesimpl.h>
      2: #include <petsc/private/linesearchimpl.h>
      3: #include <petscdmshell.h>
      4: #include <petscdraw.h>
      5: #include <petscds.h>
      6: #include <petscdmadaptor.h>
      7: #include <petscconvest.h>

      9: PetscBool         SNESRegisterAllCalled = PETSC_FALSE;
     10: PetscFunctionList SNESList              = NULL;

     12: /* Logging support */
     13: PetscClassId  SNES_CLASSID, DMSNES_CLASSID;
     14: PetscLogEvent SNES_Solve, SNES_SetUp, SNES_FunctionEval, SNES_JacobianEval, SNES_NGSEval, SNES_NGSFuncEval, SNES_NewtonALEval, SNES_NPCSolve, SNES_ObjectiveEval;

     16: /*@
     17:   SNESSetErrorIfNotConverged - Causes `SNESSolve()` to generate an error immediately if the solver has not converged.

     19:   Logically Collective

     21:   Input Parameters:
     22: + snes - iterative context obtained from `SNESCreate()`
     23: - flg  - `PETSC_TRUE` indicates you want the error generated

     25:   Options Database Key:
     26: . -snes_error_if_not_converged (true|false) - cause an immediate error condition and stop the program if the solver does not converge

     28:   Level: intermediate

     30:   Note:
     31:   Normally PETSc continues if a solver fails to converge, you can call `SNESGetConvergedReason()` after a `SNESSolve()`
     32:   to determine if it has converged. Otherwise the solution may be inaccurate or wrong

     34: .seealso: [](ch_snes), `SNES`, `SNESGetErrorIfNotConverged()`, `KSPGetErrorIfNotConverged()`, `KSPSetErrorIfNotConverged()`
     35: @*/
     36: PetscErrorCode SNESSetErrorIfNotConverged(SNES snes, PetscBool flg)
     37: {
     38:   PetscFunctionBegin;
     41:   snes->errorifnotconverged = flg;
     42:   PetscFunctionReturn(PETSC_SUCCESS);
     43: }

     45: /*@
     46:   SNESGetErrorIfNotConverged - Indicates if `SNESSolve()` will generate an error if the solver does not converge?

     48:   Not Collective

     50:   Input Parameter:
     51: . snes - iterative context obtained from `SNESCreate()`

     53:   Output Parameter:
     54: . flag - `PETSC_TRUE` if it will generate an error, else `PETSC_FALSE`

     56:   Level: intermediate

     58: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetErrorIfNotConverged()`, `KSPGetErrorIfNotConverged()`, `KSPSetErrorIfNotConverged()`
     59: @*/
     60: PetscErrorCode SNESGetErrorIfNotConverged(SNES snes, PetscBool *flag)
     61: {
     62:   PetscFunctionBegin;
     64:   PetscAssertPointer(flag, 2);
     65:   *flag = snes->errorifnotconverged;
     66:   PetscFunctionReturn(PETSC_SUCCESS);
     67: }

     69: /*@
     70:   SNESSetAlwaysComputesFinalResidual - tells the `SNES` to always compute the residual (nonlinear function value) at the final solution

     72:   Logically Collective

     74:   Input Parameters:
     75: + snes - the shell `SNES`
     76: - flg  - `PETSC_TRUE` to always compute the residual

     78:   Level: advanced

     80:   Note:
     81:   Some solvers (such as smoothers in a `SNESFAS`) do not need the residual computed at the final solution so skip computing it
     82:   to save time.

     84: .seealso: [](ch_snes), `SNES`, `SNESFAS`, `SNESSolve()`, `SNESGetAlwaysComputesFinalResidual()`
     85: @*/
     86: PetscErrorCode SNESSetAlwaysComputesFinalResidual(SNES snes, PetscBool flg)
     87: {
     88:   PetscFunctionBegin;
     90:   snes->alwayscomputesfinalresidual = flg;
     91:   PetscFunctionReturn(PETSC_SUCCESS);
     92: }

     94: /*@
     95:   SNESGetAlwaysComputesFinalResidual - checks if the `SNES` always computes the residual at the final solution

     97:   Logically Collective

     99:   Input Parameter:
    100: . snes - the `SNES` context

    102:   Output Parameter:
    103: . flg - `PETSC_TRUE` if the residual is computed

    105:   Level: advanced

    107: .seealso: [](ch_snes), `SNES`, `SNESFAS`, `SNESSolve()`, `SNESSetAlwaysComputesFinalResidual()`
    108: @*/
    109: PetscErrorCode SNESGetAlwaysComputesFinalResidual(SNES snes, PetscBool *flg)
    110: {
    111:   PetscFunctionBegin;
    113:   *flg = snes->alwayscomputesfinalresidual;
    114:   PetscFunctionReturn(PETSC_SUCCESS);
    115: }

    117: /*@
    118:   SNESSetFunctionDomainError - tells `SNES` that the input vector, a proposed new solution, to your function you provided to `SNESSetFunction()` is not
    119:   in the function's domain. For example, a step with negative pressure.

    121:   Not Collective

    123:   Input Parameter:
    124: . snes - the `SNES` context

    126:   Level: advanced

    128:   Notes:
    129:   This does not need to be called by all processes in the `SNES` MPI communicator.

    131:   A few solvers will try to cut the step size to avoid the domain error but for other solvers `SNESSolve()` stops iterating and
    132:   returns with a `SNESConvergedReason` of `SNES_DIVERGED_FUNCTION_DOMAIN`

    134:   You can direct `SNES` to avoid certain steps by using `SNESVISetVariableBounds()`, `SNESVISetComputeVariableBounds()` or
    135:   `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`

    137:   You should always call `SNESGetConvergedReason()` after each `SNESSolve()` and verify if the iteration converged (positive result) or diverged (negative result).

    139:   You can call `SNESSetJacobianDomainError()` during a Jacobian computation to indicate the proposed solution is not in the domain.

    141:   Developer Note:
    142:   This value is used by `SNESCheckFunctionDomainError()` to determine if the `SNESConvergedReason` is set to `SNES_DIVERGED_FUNCTION_DOMAIN`

    144: .seealso: [](ch_snes), `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetJacobianDomainError()`, `SNESVISetVariableBounds()`,
    145:           `SNESVISetComputeVariableBounds()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`, `SNESConvergedReason`, `SNESGetConvergedReason()`,
    146:           `SNES_DIVERGED_FUNCTION_DOMAIN`, `SNESSetObjectiveDomainError()`, `SNES_DIVERGED_OBJECTIVE_DOMAIN`
    147: @*/
    148: PetscErrorCode SNESSetFunctionDomainError(SNES snes)
    149: {
    150:   PetscFunctionBegin;
    152:   snes->functiondomainerror = PETSC_TRUE;
    153:   PetscFunctionReturn(PETSC_SUCCESS);
    154: }

    156: /*@
    157:   SNESSetObjectiveDomainError - tells `SNES` that the input vector, a proposed new solution, to your function you provided to `SNESSetObjective()` is not
    158:   in the function's domain. For example, a step with negative pressure.

    160:   Not Collective

    162:   Input Parameter:
    163: . snes - the `SNES` context

    165:   Level: advanced

    167:   Notes:
    168:   This does not need to be called by all processes in the `SNES` MPI communicator.

    170:   A few solvers will try to cut the step size to avoid the domain error but for other solvers `SNESSolve()` stops iterating and
    171:   returns with a `SNESConvergedReason` of `SNES_DIVERGED_OBJECTIVE_DOMAIN`

    173:   You can direct `SNES` to avoid certain steps by using `SNESVISetVariableBounds()`, `SNESVISetComputeVariableBounds()` or
    174:   `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`

    176:   You should always call `SNESGetConvergedReason()` after each `SNESSolve()` and verify if the iteration converged (positive result) or diverged (negative result).

    178:   You can call `SNESSetJacobianDomainError()` during a Jacobian computation to indicate the proposed solution is not in the domain.

    180:   Developer Note:
    181:   This value is used by `SNESCheckObjectiveDomainError()` to determine if the `SNESConvergedReason` is set to `SNES_DIVERGED_OBJECTIVE_DOMAIN`

    183: .seealso: [](ch_snes), `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetJacobianDomainError()`, `SNESVISetVariableBounds()`,
    184:           `SNESVISetComputeVariableBounds()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`, `SNESConvergedReason`, `SNESGetConvergedReason()`,
    185:           `SNES_DIVERGED_OBJECTIVE_DOMAIN`, `SNESSetFunctionDomainError()`, `SNES_DIVERGED_FUNCTION_DOMAIN`
    186: @*/
    187: PetscErrorCode SNESSetObjectiveDomainError(SNES snes)
    188: {
    189:   PetscFunctionBegin;
    191:   snes->objectivedomainerror = PETSC_TRUE;
    192:   PetscFunctionReturn(PETSC_SUCCESS);
    193: }

    195: /*@
    196:   SNESSetJacobianDomainError - tells `SNES` that the function you provided to `SNESSetJacobian()` at the proposed step. For example there is a negative element transformation.

    198:   Logically Collective

    200:   Input Parameter:
    201: . snes - the `SNES` context

    203:   Level: advanced

    205:   Notes:
    206:   If this is called the `SNESSolve()` stops iterating and returns with a `SNESConvergedReason` of `SNES_DIVERGED_JACOBIAN_DOMAIN`

    208:   You should always call `SNESGetConvergedReason()` after each `SNESSolve()` and verify if the iteration converged (positive result) or diverged (negative result).

    210:   You can direct `SNES` to avoid certain steps by using `SNESVISetVariableBounds()`, `SNESVISetComputeVariableBounds()` or
    211:   `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`

    213: .seealso: [](ch_snes), `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetFunctionDomainError()`, `SNESVISetVariableBounds()`,
    214:           `SNESVISetComputeVariableBounds()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`, `SNESConvergedReason`, `SNESGetConvergedReason()`
    215: @*/
    216: PetscErrorCode SNESSetJacobianDomainError(SNES snes)
    217: {
    218:   PetscFunctionBegin;
    220:   PetscCheck(!snes->errorifnotconverged, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "User code indicates computeJacobian does not make sense");
    221:   snes->jacobiandomainerror = PETSC_TRUE;
    222:   PetscFunctionReturn(PETSC_SUCCESS);
    223: }

    225: /*@
    226:   SNESSetCheckJacobianDomainError - tells `SNESSolve()` whether to check if the user called `SNESSetJacobianDomainError()` to indicate a Jacobian domain error after
    227:   each Jacobian evaluation.

    229:   Logically Collective

    231:   Input Parameters:
    232: + snes - the `SNES` context
    233: - flg  - indicates if or not to check Jacobian domain error after each Jacobian evaluation

    235:   Level: advanced

    237:   Notes:
    238:   By default, it checks for the Jacobian domain error in the debug mode, and does not check it in the optimized mode.

    240:   Checks require one extra parallel synchronization for each Jacobian evaluation

    242: .seealso: [](ch_snes), `SNES`, `SNESConvergedReason`, `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetFunctionDomainError()`, `SNESGetCheckJacobianDomainError()`
    243: @*/
    244: PetscErrorCode SNESSetCheckJacobianDomainError(SNES snes, PetscBool flg)
    245: {
    246:   PetscFunctionBegin;
    248:   snes->checkjacdomainerror = flg;
    249:   PetscFunctionReturn(PETSC_SUCCESS);
    250: }

    252: /*@
    253:   SNESGetCheckJacobianDomainError - Get an indicator whether or not `SNES` is checking Jacobian domain errors after each Jacobian evaluation.

    255:   Logically Collective

    257:   Input Parameter:
    258: . snes - the `SNES` context

    260:   Output Parameter:
    261: . flg - `PETSC_FALSE` indicates that it is not checking Jacobian domain errors after each Jacobian evaluation

    263:   Level: advanced

    265: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetFunctionDomainError()`, `SNESSetCheckJacobianDomainError()`
    266: @*/
    267: PetscErrorCode SNESGetCheckJacobianDomainError(SNES snes, PetscBool *flg)
    268: {
    269:   PetscFunctionBegin;
    271:   PetscAssertPointer(flg, 2);
    272:   *flg = snes->checkjacdomainerror;
    273:   PetscFunctionReturn(PETSC_SUCCESS);
    274: }

    276: /*@
    277:   SNESLoad - Loads a `SNES` that has been stored in `PETSCVIEWERBINARY` with `SNESView()`.

    279:   Collective

    281:   Input Parameters:
    282: + snes   - the newly loaded `SNES`, this needs to have been created with `SNESCreate()` or
    283:            some related function before a call to `SNESLoad()`.
    284: - viewer - binary file viewer, obtained from `PetscViewerBinaryOpen()`

    286:   Level: intermediate

    288:   Note:
    289:   The `SNESType` is determined by the data in the file, any type set into the `SNES` before this call is ignored.

    291: .seealso: [](ch_snes), `SNES`, `PetscViewer`, `SNESCreate()`, `SNESType`, `PetscViewerBinaryOpen()`, `SNESView()`, `MatLoad()`, `VecLoad()`
    292: @*/
    293: PetscErrorCode SNESLoad(SNES snes, PetscViewer viewer)
    294: {
    295:   PetscBool isbinary;
    296:   PetscInt  classid;
    297:   char      type[256];
    298:   KSP       ksp;
    299:   DM        dm;
    300:   DMSNES    dmsnes;

    302:   PetscFunctionBegin;
    305:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERBINARY, &isbinary));
    306:   PetscCheck(isbinary, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONG, "Invalid viewer; open viewer with PetscViewerBinaryOpen()");

    308:   PetscCall(PetscViewerBinaryRead(viewer, &classid, 1, NULL, PETSC_INT));
    309:   PetscCheck(classid == SNES_FILE_CLASSID, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_WRONG, "Not SNES next in file");
    310:   PetscCall(PetscViewerBinaryRead(viewer, type, 256, NULL, PETSC_CHAR));
    311:   PetscCall(SNESSetType(snes, type));
    312:   PetscTryTypeMethod(snes, load, viewer);
    313:   PetscCall(SNESGetDM(snes, &dm));
    314:   PetscCall(DMGetDMSNES(dm, &dmsnes));
    315:   PetscCall(DMSNESLoad(dmsnes, viewer));
    316:   PetscCall(SNESGetKSP(snes, &ksp));
    317:   PetscCall(KSPLoad(ksp, viewer));
    318:   PetscFunctionReturn(PETSC_SUCCESS);
    319: }

    321: #include <petscdraw.h>
    322: #if defined(PETSC_HAVE_SAWS)
    323: #include <petscviewersaws.h>
    324: #endif

    326: /*@
    327:   SNESViewFromOptions - View a `SNES` based on values in the options database

    329:   Collective

    331:   Input Parameters:
    332: + A    - the `SNES` context
    333: . obj  - Optional object that provides the options prefix for the checks
    334: - name - command line option

    336:   Options Database Key:
    337: . -name [viewertype][:...] - option name and values. See `PetscObjectViewFromOptions()` for the possible arguments

    339:   Level: intermediate

    341: .seealso: [](ch_snes), `SNES`, `SNESView`, `PetscObjectViewFromOptions()`, `SNESCreate()`
    342: @*/
    343: PetscErrorCode SNESViewFromOptions(SNES A, PetscObject obj, const char name[])
    344: {
    345:   PetscFunctionBegin;
    347:   PetscCall(PetscObjectViewFromOptions((PetscObject)A, obj, name));
    348:   PetscFunctionReturn(PETSC_SUCCESS);
    349: }

    351: PETSC_EXTERN PetscErrorCode SNESComputeJacobian_DMDA(SNES, Vec, Mat, Mat, void *);

    353: /*@
    354:   SNESView - Prints or visualizes the `SNES` data structure.

    356:   Collective

    358:   Input Parameters:
    359: + snes   - the `SNES` context
    360: - viewer - the `PetscViewer`

    362:   Options Database Key:
    363: . -snes_view - Calls `SNESView()` at end of `SNESSolve()`

    365:   Level: beginner

    367:   Notes:
    368:   The available visualization contexts include
    369: +     `PETSC_VIEWER_STDOUT_SELF` - standard output (default)
    370: -     `PETSC_VIEWER_STDOUT_WORLD` - synchronized standard
    371:   output where only the first processor opens
    372:   the file.  All other processors send their
    373:   data to the first processor to print.

    375:   The available formats include
    376: +     `PETSC_VIEWER_DEFAULT` - standard output (default)
    377: -     `PETSC_VIEWER_ASCII_INFO_DETAIL` - more verbose output for `SNESNASM`

    379:   The user can open an alternative visualization context with
    380:   `PetscViewerASCIIOpen()` - output to a specified file.

    382:   In the debugger you can do "call `SNESView`(snes,0)" to display the `SNES` solver. (The same holds for any PETSc object viewer).

    384: .seealso: [](ch_snes), `SNES`, `SNESLoad()`, `SNESCreate()`, `PetscViewerASCIIOpen()`
    385: @*/
    386: PetscErrorCode SNESView(SNES snes, PetscViewer viewer)
    387: {
    388:   SNESKSPEW     *kctx;
    389:   KSP            ksp;
    390:   SNESLineSearch linesearch;
    391:   PetscBool      isascii, isstring, isbinary, isdraw;
    392:   DMSNES         dmsnes;
    393: #if defined(PETSC_HAVE_SAWS)
    394:   PetscBool issaws;
    395: #endif

    397:   PetscFunctionBegin;
    399:   if (!viewer) PetscCall(PetscViewerASCIIGetStdout(PetscObjectComm((PetscObject)snes), &viewer));
    401:   PetscCheckSameComm(snes, 1, viewer, 2);

    403:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &isascii));
    404:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERSTRING, &isstring));
    405:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERBINARY, &isbinary));
    406:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERDRAW, &isdraw));
    407: #if defined(PETSC_HAVE_SAWS)
    408:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERSAWS, &issaws));
    409: #endif
    410:   if (isascii) {
    411:     SNESNormSchedule normschedule;
    412:     DM               dm;
    413:     SNESJacobianFn  *cJ;
    414:     void            *ctx;
    415:     const char      *pre = "";

    417:     PetscCall(PetscObjectPrintClassNamePrefixType((PetscObject)snes, viewer));
    418:     if (!snes->setupcalled) PetscCall(PetscViewerASCIIPrintf(viewer, "  SNES has not been set up so information may be incomplete\n"));
    419:     if (snes->ops->view) {
    420:       PetscCall(PetscViewerASCIIPushTab(viewer));
    421:       PetscUseTypeMethod(snes, view, viewer);
    422:       PetscCall(PetscViewerASCIIPopTab(viewer));
    423:     }
    424:     if (snes->max_funcs == PETSC_UNLIMITED) {
    425:       PetscCall(PetscViewerASCIIPrintf(viewer, "  maximum iterations=%" PetscInt_FMT ", maximum function evaluations=unlimited\n", snes->max_its));
    426:     } else {
    427:       PetscCall(PetscViewerASCIIPrintf(viewer, "  maximum iterations=%" PetscInt_FMT ", maximum function evaluations=%" PetscInt_FMT "\n", snes->max_its, snes->max_funcs));
    428:     }
    429:     PetscCall(PetscViewerASCIIPrintf(viewer, "  tolerances: relative=%g, absolute=%g, solution=%g\n", (double)snes->rtol, (double)snes->abstol, (double)snes->stol));
    430:     if (snes->usesksp) PetscCall(PetscViewerASCIIPrintf(viewer, "  total number of linear solver iterations=%" PetscInt_FMT "\n", snes->linear_its));
    431:     PetscCall(PetscViewerASCIIPrintf(viewer, "  total number of function evaluations=%" PetscInt_FMT "\n", snes->nfuncs));
    432:     PetscCall(SNESGetNormSchedule(snes, &normschedule));
    433:     if (normschedule > 0) PetscCall(PetscViewerASCIIPrintf(viewer, "  norm schedule %s\n", SNESNormSchedules[normschedule]));
    434:     if (snes->gridsequence) PetscCall(PetscViewerASCIIPrintf(viewer, "  total number of grid sequence refinements=%" PetscInt_FMT "\n", snes->gridsequence));
    435:     if (snes->ksp_ewconv) {
    436:       kctx = (SNESKSPEW *)snes->kspconvctx;
    437:       if (kctx) {
    438:         PetscCall(PetscViewerASCIIPrintf(viewer, "  Eisenstat-Walker computation of KSP relative tolerance (version %" PetscInt_FMT ")\n", kctx->version));
    439:         PetscCall(PetscViewerASCIIPrintf(viewer, "    rtol_0=%g, rtol_max=%g, threshold=%g\n", (double)kctx->rtol_0, (double)kctx->rtol_max, (double)kctx->threshold));
    440:         PetscCall(PetscViewerASCIIPrintf(viewer, "    gamma=%g, alpha=%g, alpha2=%g\n", (double)kctx->gamma, (double)kctx->alpha, (double)kctx->alpha2));
    441:       }
    442:     }
    443:     if (snes->lagpreconditioner == -1) {
    444:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Preconditioned is never rebuilt\n"));
    445:     } else if (snes->lagpreconditioner > 1) {
    446:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Preconditioned is rebuilt every %" PetscInt_FMT " new Jacobians\n", snes->lagpreconditioner));
    447:     }
    448:     if (snes->lagjacobian == -1) {
    449:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Jacobian is never rebuilt\n"));
    450:     } else if (snes->lagjacobian > 1) {
    451:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Jacobian is rebuilt every %" PetscInt_FMT " SNES iterations\n", snes->lagjacobian));
    452:     }
    453:     PetscCall(SNESGetDM(snes, &dm));
    454:     PetscCall(DMSNESGetJacobian(dm, &cJ, &ctx));
    455:     if (snes->mf_operator) {
    456:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Jacobian is applied matrix-free with differencing\n"));
    457:       pre = "Preconditioning ";
    458:     }
    459:     if (cJ == SNESComputeJacobianDefault) {
    460:       PetscCall(PetscViewerASCIIPrintf(viewer, "  %sJacobian is built using finite differences one column at a time\n", pre));
    461:     } else if (cJ == SNESComputeJacobianDefaultColor) {
    462:       PetscCall(PetscViewerASCIIPrintf(viewer, "  %sJacobian is built using finite differences with coloring\n", pre));
    463:       /* it slightly breaks data encapsulation for access the DMDA information directly */
    464:     } else if (cJ == SNESComputeJacobian_DMDA) {
    465:       MatFDColoring fdcoloring;
    466:       PetscCall(PetscObjectQuery((PetscObject)dm, "DMDASNES_FDCOLORING", (PetscObject *)&fdcoloring));
    467:       if (fdcoloring) {
    468:         PetscCall(PetscViewerASCIIPrintf(viewer, "  %sJacobian is built using colored finite differences on a DMDA\n", pre));
    469:       } else {
    470:         PetscCall(PetscViewerASCIIPrintf(viewer, "  %sJacobian is built using a DMDA local Jacobian\n", pre));
    471:       }
    472:     } else if (snes->mf && !snes->mf_operator) {
    473:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Jacobian is applied matrix-free with differencing, no explicit Jacobian\n"));
    474:     }
    475:   } else if (isstring) {
    476:     const char *type;
    477:     PetscCall(SNESGetType(snes, &type));
    478:     PetscCall(PetscViewerStringSPrintf(viewer, " SNESType: %-7.7s", type));
    479:     PetscTryTypeMethod(snes, view, viewer);
    480:   } else if (isbinary) {
    481:     PetscInt    classid = SNES_FILE_CLASSID;
    482:     MPI_Comm    comm;
    483:     PetscMPIInt rank;
    484:     char        type[256];

    486:     PetscCall(PetscObjectGetComm((PetscObject)snes, &comm));
    487:     PetscCallMPI(MPI_Comm_rank(comm, &rank));
    488:     if (rank == 0) {
    489:       PetscCall(PetscViewerBinaryWrite(viewer, &classid, 1, PETSC_INT));
    490:       PetscCall(PetscStrncpy(type, ((PetscObject)snes)->type_name, sizeof(type)));
    491:       PetscCall(PetscViewerBinaryWrite(viewer, type, sizeof(type), PETSC_CHAR));
    492:     }
    493:     PetscTryTypeMethod(snes, view, viewer);
    494:   } else if (isdraw) {
    495:     PetscDraw draw;
    496:     char      str[36];
    497:     PetscReal x, y, bottom, h;

    499:     PetscCall(PetscViewerDrawGetDraw(viewer, 0, &draw));
    500:     PetscCall(PetscDrawGetCurrentPoint(draw, &x, &y));
    501:     PetscCall(PetscStrncpy(str, "SNES: ", sizeof(str)));
    502:     PetscCall(PetscStrlcat(str, ((PetscObject)snes)->type_name, sizeof(str)));
    503:     PetscCall(PetscDrawStringBoxed(draw, x, y, PETSC_DRAW_BLUE, PETSC_DRAW_BLACK, str, NULL, &h));
    504:     bottom = y - h;
    505:     PetscCall(PetscDrawPushCurrentPoint(draw, x, bottom));
    506:     PetscTryTypeMethod(snes, view, viewer);
    507: #if defined(PETSC_HAVE_SAWS)
    508:   } else if (issaws) {
    509:     PetscMPIInt rank;
    510:     const char *name;

    512:     PetscCall(PetscObjectGetName((PetscObject)snes, &name));
    513:     PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
    514:     if (!((PetscObject)snes)->amsmem && rank == 0) {
    515:       char dir[1024];

    517:       PetscCall(PetscObjectViewSAWs((PetscObject)snes, viewer));
    518:       PetscCall(PetscSNPrintf(dir, 1024, "/PETSc/Objects/%s/its", name));
    519:       PetscCallSAWs(SAWs_Register, (dir, &snes->iter, 1, SAWs_READ, SAWs_INT));
    520:       if (!snes->conv_hist) PetscCall(SNESSetConvergenceHistory(snes, NULL, NULL, PETSC_DECIDE, PETSC_TRUE));
    521:       PetscCall(PetscSNPrintf(dir, 1024, "/PETSc/Objects/%s/conv_hist", name));
    522:       PetscCallSAWs(SAWs_Register, (dir, snes->conv_hist, 10, SAWs_READ, SAWs_DOUBLE));
    523:     }
    524: #endif
    525:   }
    526:   if (snes->linesearch) {
    527:     PetscCall(SNESGetLineSearch(snes, &linesearch));
    528:     PetscCall(PetscViewerASCIIPushTab(viewer));
    529:     PetscCall(SNESLineSearchView(linesearch, viewer));
    530:     PetscCall(PetscViewerASCIIPopTab(viewer));
    531:   }
    532:   if (snes->npc && snes->usesnpc) {
    533:     PetscCall(PetscViewerASCIIPushTab(viewer));
    534:     PetscCall(SNESView(snes->npc, viewer));
    535:     PetscCall(PetscViewerASCIIPopTab(viewer));
    536:   }
    537:   PetscCall(PetscViewerASCIIPushTab(viewer));
    538:   PetscCall(DMGetDMSNES(snes->dm, &dmsnes));
    539:   PetscCall(DMSNESView(dmsnes, viewer));
    540:   PetscCall(PetscViewerASCIIPopTab(viewer));
    541:   if (snes->usesksp) {
    542:     PetscCall(SNESGetKSP(snes, &ksp));
    543:     PetscCall(PetscViewerASCIIPushTab(viewer));
    544:     PetscCall(KSPView(ksp, viewer));
    545:     PetscCall(PetscViewerASCIIPopTab(viewer));
    546:   }
    547:   if (isdraw) {
    548:     PetscDraw draw;
    549:     PetscCall(PetscViewerDrawGetDraw(viewer, 0, &draw));
    550:     PetscCall(PetscDrawPopCurrentPoint(draw));
    551:   }
    552:   PetscFunctionReturn(PETSC_SUCCESS);
    553: }

    555: /*
    556:   We retain a list of functions that also take SNES command
    557:   line options. These are called at the end SNESSetFromOptions()
    558: */
    559: #define MAXSETFROMOPTIONS 5
    560: static PetscInt numberofsetfromoptions;
    561: static PetscErrorCode (*othersetfromoptions[MAXSETFROMOPTIONS])(SNES);

    563: /*@C
    564:   SNESAddOptionsChecker - Adds an additional function to check for `SNES` options.

    566:   Not Collective

    568:   Input Parameter:
    569: . snescheck - function that checks for options

    571:   Calling sequence of `snescheck`:
    572: . snes - the `SNES` object for which it is checking options

    574:   Level: developer

    576: .seealso: [](ch_snes), `SNES`, `SNESSetFromOptions()`
    577: @*/
    578: PetscErrorCode SNESAddOptionsChecker(PetscErrorCode (*snescheck)(SNES snes))
    579: {
    580:   PetscFunctionBegin;
    581:   PetscCheck(numberofsetfromoptions < MAXSETFROMOPTIONS, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Too many options checkers, only %d allowed", MAXSETFROMOPTIONS);
    582:   othersetfromoptions[numberofsetfromoptions++] = snescheck;
    583:   PetscFunctionReturn(PETSC_SUCCESS);
    584: }

    586: static PetscErrorCode SNESSetUpMatrixFree_Private(SNES snes, PetscBool hasOperator, PetscInt version)
    587: {
    588:   Mat          J;
    589:   MatNullSpace nullsp;

    591:   PetscFunctionBegin;

    594:   if (!snes->vec_func && (snes->jacobian || snes->jacobian_pre)) {
    595:     Mat A = snes->jacobian, B = snes->jacobian_pre;
    596:     PetscCall(MatCreateVecs(A ? A : B, NULL, &snes->vec_func));
    597:   }

    599:   PetscCheck(version == 1 || version == 2, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "matrix-free operator routines, only version 1 and 2");
    600:   if (version == 1) {
    601:     PetscCall(MatCreateSNESMF(snes, &J));
    602:     PetscCall(MatMFFDSetOptionsPrefix(J, ((PetscObject)snes)->prefix));
    603:     PetscCall(MatSetFromOptions(J));
    604:     /* TODO: the version 2 code should be merged into the MatCreateSNESMF() and MatCreateMFFD() infrastructure and then removed */
    605:   } else /* if (version == 2) */ {
    606:     PetscCheck(snes->vec_func, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "SNESSetFunction() must be called first");
    607: #if !defined(PETSC_USE_COMPLEX) && !defined(PETSC_USE_REAL_SINGLE) && !defined(PETSC_USE_REAL___FLOAT128) && !defined(PETSC_USE_REAL___FP16)
    608:     PetscCall(MatCreateSNESMFMore(snes, snes->vec_func, &J));
    609: #else
    610:     SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SUP, "matrix-free operator routines (version 2)");
    611: #endif
    612:   }

    614:   /* attach any user provided null space that was on Amat to the newly created matrix-free matrix */
    615:   if (snes->jacobian) {
    616:     PetscCall(MatGetNullSpace(snes->jacobian, &nullsp));
    617:     if (nullsp) PetscCall(MatSetNullSpace(J, nullsp));
    618:   }

    620:   PetscCall(PetscInfo(snes, "Setting default matrix-free operator routines (version %" PetscInt_FMT ")\n", version));
    621:   if (hasOperator) {
    622:     /* This version replaces the user provided Jacobian matrix with a
    623:        matrix-free version but still employs the user-provided matrix used for computing the preconditioner. */
    624:     PetscCall(SNESSetJacobian(snes, J, NULL, NULL, NULL));
    625:   } else {
    626:     /* This version replaces both the user-provided Jacobian and the user-
    627:      provided preconditioner Jacobian with the default matrix-free version. */
    628:     if (snes->npcside == PC_LEFT && snes->npc) {
    629:       if (!snes->jacobian) PetscCall(SNESSetJacobian(snes, J, NULL, NULL, NULL));
    630:     } else {
    631:       KSP       ksp;
    632:       PC        pc;
    633:       PetscBool match;

    635:       PetscCall(SNESSetJacobian(snes, J, J, MatMFFDComputeJacobian, NULL));
    636:       /* Force no preconditioner */
    637:       PetscCall(SNESGetKSP(snes, &ksp));
    638:       PetscCall(KSPGetPC(ksp, &pc));
    639:       PetscCall(PetscObjectTypeCompareAny((PetscObject)pc, &match, PCSHELL, PCH2OPUS, ""));
    640:       if (!match) {
    641:         PetscCall(PetscInfo(snes, "Setting default matrix-free preconditioner routines\nThat is no preconditioner is being used\n"));
    642:         PetscCall(PCSetType(pc, PCNONE));
    643:       }
    644:     }
    645:   }
    646:   PetscCall(MatDestroy(&J));
    647:   PetscFunctionReturn(PETSC_SUCCESS);
    648: }

    650: static PetscErrorCode DMRestrictHook_SNESVecSol(DM dmfine, Mat Restrict, Vec Rscale, Mat Inject, DM dmcoarse, PetscCtx ctx)
    651: {
    652:   SNES snes = (SNES)ctx;
    653:   Vec  Xfine, Xfine_named = NULL, Xcoarse;

    655:   PetscFunctionBegin;
    656:   if (PetscLogPrintInfo) {
    657:     PetscInt finelevel, coarselevel, fineclevel, coarseclevel;
    658:     PetscCall(DMGetRefineLevel(dmfine, &finelevel));
    659:     PetscCall(DMGetCoarsenLevel(dmfine, &fineclevel));
    660:     PetscCall(DMGetRefineLevel(dmcoarse, &coarselevel));
    661:     PetscCall(DMGetCoarsenLevel(dmcoarse, &coarseclevel));
    662:     PetscCall(PetscInfo(dmfine, "Restricting SNES solution vector from level %" PetscInt_FMT "-%" PetscInt_FMT " to level %" PetscInt_FMT "-%" PetscInt_FMT "\n", finelevel, fineclevel, coarselevel, coarseclevel));
    663:   }
    664:   if (dmfine == snes->dm) Xfine = snes->vec_sol;
    665:   else {
    666:     PetscCall(DMGetNamedGlobalVector(dmfine, "SNESVecSol", &Xfine_named));
    667:     Xfine = Xfine_named;
    668:   }
    669:   PetscCall(DMGetNamedGlobalVector(dmcoarse, "SNESVecSol", &Xcoarse));
    670:   if (Inject) {
    671:     PetscCall(MatRestrict(Inject, Xfine, Xcoarse));
    672:   } else {
    673:     PetscCall(MatRestrict(Restrict, Xfine, Xcoarse));
    674:     PetscCall(VecPointwiseMult(Xcoarse, Xcoarse, Rscale));
    675:   }
    676:   PetscCall(DMRestoreNamedGlobalVector(dmcoarse, "SNESVecSol", &Xcoarse));
    677:   if (Xfine_named) PetscCall(DMRestoreNamedGlobalVector(dmfine, "SNESVecSol", &Xfine_named));
    678:   PetscFunctionReturn(PETSC_SUCCESS);
    679: }

    681: static PetscErrorCode DMCoarsenHook_SNESVecSol(DM dm, DM dmc, PetscCtx ctx)
    682: {
    683:   PetscFunctionBegin;
    684:   PetscCall(DMCoarsenHookAdd(dmc, DMCoarsenHook_SNESVecSol, DMRestrictHook_SNESVecSol, ctx));
    685:   PetscFunctionReturn(PETSC_SUCCESS);
    686: }

    688: /* This may be called to rediscretize the operator on levels of linear multigrid. The DM shuffle is so the user can
    689:  * safely call SNESGetDM() in their residual evaluation routine. */
    690: static PetscErrorCode KSPComputeOperators_SNES(KSP ksp, Mat A, Mat B, PetscCtx ctx)
    691: {
    692:   SNES            snes = (SNES)ctx;
    693:   DMSNES          sdm;
    694:   Vec             X, Xnamed = NULL;
    695:   DM              dmsave;
    696:   void           *ctxsave;
    697:   SNESJacobianFn *jac = NULL;

    699:   PetscFunctionBegin;
    700:   dmsave = snes->dm;
    701:   PetscCall(KSPGetDM(ksp, &snes->dm));
    702:   if (dmsave == snes->dm) X = snes->vec_sol; /* We are on the finest level */
    703:   else {
    704:     PetscBool has;

    706:     /* We are on a coarser level, this vec was initialized using a DM restrict hook */
    707:     PetscCall(DMHasNamedGlobalVector(snes->dm, "SNESVecSol", &has));
    708:     PetscCheck(has, PetscObjectComm((PetscObject)snes->dm), PETSC_ERR_PLIB, "Missing SNESVecSol");
    709:     PetscCall(DMGetNamedGlobalVector(snes->dm, "SNESVecSol", &Xnamed));
    710:     X = Xnamed;
    711:     PetscCall(SNESGetJacobian(snes, NULL, NULL, &jac, &ctxsave));
    712:     /* If the DM's don't match up, the MatFDColoring context needed for the jacobian won't match up either -- fixit. */
    713:     if (jac == SNESComputeJacobianDefaultColor) PetscCall(SNESSetJacobian(snes, NULL, NULL, SNESComputeJacobianDefaultColor, NULL));
    714:   }

    716:   /* Compute the operators */
    717:   PetscCall(DMGetDMSNES(snes->dm, &sdm));
    718:   if (Xnamed && sdm->ops->computefunction) {
    719:     /* The SNES contract with the user is that ComputeFunction is always called before ComputeJacobian.
    720:        We make sure of this here. Disable affine shift since it is for the finest level */
    721:     Vec F, saverhs = snes->vec_rhs;

    723:     snes->vec_rhs = NULL;
    724:     PetscCall(DMGetGlobalVector(snes->dm, &F));
    725:     PetscCall(SNESComputeFunction(snes, X, F));
    726:     PetscCall(DMRestoreGlobalVector(snes->dm, &F));
    727:     snes->vec_rhs = saverhs;
    728:     snes->nfuncs--; /* Do not log coarser level evaluations */
    729:   }
    730:   /* Make sure KSP DM has the Jacobian computation routine */
    731:   if (!sdm->ops->computejacobian) PetscCall(DMCopyDMSNES(dmsave, snes->dm));
    732:   PetscCall(SNESComputeJacobian(snes, X, A, B)); /* cannot handle previous SNESSetJacobianDomainError() calls */

    734:   /* Put the previous context back */
    735:   if (snes->dm != dmsave && jac == SNESComputeJacobianDefaultColor) PetscCall(SNESSetJacobian(snes, NULL, NULL, jac, ctxsave));

    737:   if (Xnamed) PetscCall(DMRestoreNamedGlobalVector(snes->dm, "SNESVecSol", &Xnamed));
    738:   snes->dm = dmsave;
    739:   PetscFunctionReturn(PETSC_SUCCESS);
    740: }

    742: /*@
    743:   SNESSetUpMatrices - ensures that matrices are available for `SNES` Newton-like methods, this is called by `SNESSetUp_XXX()`

    745:   Collective

    747:   Input Parameter:
    748: . snes - `SNES` object to configure

    750:   Level: developer

    752:   Note:
    753:   If the matrices do not yet exist it attempts to create them based on options previously set for the `SNES` such as `-snes_mf`

    755:   Developer Note:
    756:   The functionality of this routine overlaps in a confusing way with the functionality of `SNESSetUpMatrixFree_Private()` which is called by
    757:   `SNESSetUp()` but sometimes `SNESSetUpMatrices()` is called without `SNESSetUp()` being called. A refactorization to simplify the
    758:   logic that handles the matrix-free case is desirable.

    760: .seealso: [](ch_snes), `SNES`, `SNESSetUp()`
    761: @*/
    762: PetscErrorCode SNESSetUpMatrices(SNES snes)
    763: {
    764:   DM     dm;
    765:   DMSNES sdm;

    767:   PetscFunctionBegin;
    768:   PetscCall(SNESGetDM(snes, &dm));
    769:   PetscCall(DMGetDMSNES(dm, &sdm));
    770:   if (!snes->jacobian && snes->mf && !snes->mf_operator && !snes->jacobian_pre) {
    771:     Mat   J;
    772:     void *functx;
    773:     PetscCall(MatCreateSNESMF(snes, &J));
    774:     PetscCall(MatMFFDSetOptionsPrefix(J, ((PetscObject)snes)->prefix));
    775:     PetscCall(MatSetFromOptions(J));
    776:     PetscCall(SNESGetFunction(snes, NULL, NULL, &functx));
    777:     PetscCall(SNESSetJacobian(snes, J, J, NULL, NULL));
    778:     PetscCall(MatDestroy(&J));
    779:   } else if (snes->mf_operator && !snes->jacobian_pre && !snes->jacobian) {
    780:     Mat J, B;
    781:     PetscCall(MatCreateSNESMF(snes, &J));
    782:     PetscCall(MatMFFDSetOptionsPrefix(J, ((PetscObject)snes)->prefix));
    783:     PetscCall(MatSetFromOptions(J));
    784:     PetscCall(DMCreateMatrix(snes->dm, &B));
    785:     /* sdm->computejacobian was already set to reach here */
    786:     PetscCall(SNESSetJacobian(snes, J, B, NULL, NULL));
    787:     PetscCall(MatDestroy(&J));
    788:     PetscCall(MatDestroy(&B));
    789:   } else if (!snes->jacobian_pre) {
    790:     PetscDS   prob;
    791:     Mat       J, B;
    792:     PetscBool hasPrec = PETSC_FALSE;

    794:     J = snes->jacobian;
    795:     PetscCall(DMGetDS(dm, &prob));
    796:     if (prob) PetscCall(PetscDSHasJacobianPreconditioner(prob, &hasPrec));
    797:     if (!J && hasPrec) PetscCall(DMCreateMatrix(snes->dm, &J));
    798:     else PetscCall(PetscObjectReference((PetscObject)J));
    799:     PetscCall(DMCreateMatrix(snes->dm, &B));
    800:     PetscCall(SNESSetJacobian(snes, J ? J : B, B, NULL, NULL));
    801:     PetscCall(MatDestroy(&J));
    802:     PetscCall(MatDestroy(&B));
    803:   }
    804:   {
    805:     KSP ksp;
    806:     PetscCall(SNESGetKSP(snes, &ksp));
    807:     PetscCall(KSPSetComputeOperators(ksp, KSPComputeOperators_SNES, snes));
    808:     PetscCall(DMCoarsenHookAdd(snes->dm, DMCoarsenHook_SNESVecSol, DMRestrictHook_SNESVecSol, snes));
    809:   }
    810:   PetscFunctionReturn(PETSC_SUCCESS);
    811: }

    813: PETSC_SINGLE_LIBRARY_INTERN PetscErrorCode PetscMonitorPauseFinal_Internal(PetscInt, PetscCtx);

    815: static PetscErrorCode SNESMonitorPauseFinal_Internal(SNES snes)
    816: {
    817:   PetscFunctionBegin;
    818:   if (!snes->pauseFinal) PetscFunctionReturn(PETSC_SUCCESS);
    819:   PetscCall(PetscMonitorPauseFinal_Internal(snes->numbermonitors, snes->monitorcontext));
    820:   PetscFunctionReturn(PETSC_SUCCESS);
    821: }

    823: /*@C
    824:   SNESMonitorSetFromOptions - Sets a monitor function and viewer appropriate for the type indicated by the user

    826:   Collective

    828:   Input Parameters:
    829: + snes         - `SNES` object you wish to monitor
    830: . name         - the monitor type one is seeking
    831: . help         - message indicating what monitoring is done
    832: . manual       - manual page for the monitor
    833: . monitor      - the monitor function, this must use a `PetscViewerFormat` as its context
    834: - monitorsetup - a function that is called once ONLY if the user selected this monitor that may set additional features of the `SNES` or `PetscViewer` objects

    836:   Calling sequence of `monitor`:
    837: + snes - the nonlinear solver context
    838: . it   - the current iteration
    839: . r    - the current function norm
    840: - vf   - a `PetscViewerAndFormat` struct that contains the `PetscViewer` and `PetscViewerFormat` to use

    842:   Calling sequence of `monitorsetup`:
    843: + snes - the nonlinear solver context
    844: - vf   - a `PetscViewerAndFormat` struct that contains the `PetscViewer` and `PetscViewerFormat` to use

    846:   Options Database Key:
    847: . -name - trigger the use of this monitor in `SNESSetFromOptions()`

    849:   Level: advanced

    851: .seealso: [](ch_snes), `PetscOptionsCreateViewer()`, `PetscOptionsGetReal()`, `PetscOptionsHasName()`, `PetscOptionsGetString()`,
    852:           `PetscOptionsGetIntArray()`, `PetscOptionsGetRealArray()`, `PetscOptionsBool()`,
    853:           `PetscOptionsInt()`, `PetscOptionsString()`, `PetscOptionsReal()`,
    854:           `PetscOptionsName()`, `PetscOptionsBegin()`, `PetscOptionsEnd()`, `PetscOptionsHeadBegin()`,
    855:           `PetscOptionsStringArray()`, `PetscOptionsRealArray()`, `PetscOptionsScalar()`,
    856:           `PetscOptionsBoolGroupBegin()`, `PetscOptionsBoolGroup()`, `PetscOptionsBoolGroupEnd()`,
    857:           `PetscOptionsFList()`, `PetscOptionsEList()`
    858: @*/
    859: PetscErrorCode SNESMonitorSetFromOptions(SNES snes, const char name[], const char help[], const char manual[], PetscErrorCode (*monitor)(SNES snes, PetscInt it, PetscReal r, PetscViewerAndFormat *vf), PetscErrorCode (*monitorsetup)(SNES snes, PetscViewerAndFormat *vf))
    860: {
    861:   PetscViewer       viewer;
    862:   PetscViewerFormat format;
    863:   PetscBool         flg;

    865:   PetscFunctionBegin;
    866:   PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, name, &viewer, &format, &flg));
    867:   if (flg) {
    868:     PetscViewerAndFormat *vf;
    869:     PetscCall(PetscViewerAndFormatCreate(viewer, format, &vf));
    870:     PetscCall(PetscViewerDestroy(&viewer));
    871:     if (monitorsetup) PetscCall((*monitorsetup)(snes, vf));
    872:     PetscCall(SNESMonitorSet(snes, (PetscErrorCode (*)(SNES, PetscInt, PetscReal, PetscCtx))monitor, vf, (PetscCtxDestroyFn *)PetscViewerAndFormatDestroy));
    873:   }
    874:   PetscFunctionReturn(PETSC_SUCCESS);
    875: }

    877: PetscErrorCode SNESEWSetFromOptions_Private(SNESKSPEW *kctx, PetscBool print_api, MPI_Comm comm, const char *prefix)
    878: {
    879:   const char *api = print_api ? "SNESKSPSetParametersEW" : NULL;

    881:   PetscFunctionBegin;
    882:   PetscOptionsBegin(comm, prefix, "Eisenstat and Walker type forcing options", "KSP");
    883:   PetscCall(PetscOptionsInt("-ksp_ew_version", "Version 1, 2 or 3", api, kctx->version, &kctx->version, NULL));
    884:   PetscCall(PetscOptionsReal("-ksp_ew_rtol0", "0 <= rtol0 < 1", api, kctx->rtol_0, &kctx->rtol_0, NULL));
    885:   kctx->rtol_max = PetscMax(kctx->rtol_0, kctx->rtol_max);
    886:   PetscCall(PetscOptionsReal("-ksp_ew_rtolmax", "0 <= rtolmax < 1", api, kctx->rtol_max, &kctx->rtol_max, NULL));
    887:   PetscCall(PetscOptionsReal("-ksp_ew_gamma", "0 <= gamma <= 1", api, kctx->gamma, &kctx->gamma, NULL));
    888:   PetscCall(PetscOptionsReal("-ksp_ew_alpha", "1 < alpha <= 2", api, kctx->alpha, &kctx->alpha, NULL));
    889:   PetscCall(PetscOptionsReal("-ksp_ew_alpha2", "alpha2", NULL, kctx->alpha2, &kctx->alpha2, NULL));
    890:   PetscCall(PetscOptionsReal("-ksp_ew_threshold", "0 < threshold < 1", api, kctx->threshold, &kctx->threshold, NULL));
    891:   PetscCall(PetscOptionsReal("-ksp_ew_v4_p1", "p1", NULL, kctx->v4_p1, &kctx->v4_p1, NULL));
    892:   PetscCall(PetscOptionsReal("-ksp_ew_v4_p2", "p2", NULL, kctx->v4_p2, &kctx->v4_p2, NULL));
    893:   PetscCall(PetscOptionsReal("-ksp_ew_v4_p3", "p3", NULL, kctx->v4_p3, &kctx->v4_p3, NULL));
    894:   PetscCall(PetscOptionsReal("-ksp_ew_v4_m1", "Scaling when rk-1 in [p2,p3)", NULL, kctx->v4_m1, &kctx->v4_m1, NULL));
    895:   PetscCall(PetscOptionsReal("-ksp_ew_v4_m2", "Scaling when rk-1 in [p3,+infty)", NULL, kctx->v4_m2, &kctx->v4_m2, NULL));
    896:   PetscCall(PetscOptionsReal("-ksp_ew_v4_m3", "Threshold for successive rtol (0.1 in Eq.7)", NULL, kctx->v4_m3, &kctx->v4_m3, NULL));
    897:   PetscCall(PetscOptionsReal("-ksp_ew_v4_m4", "Adaptation scaling (0.5 in Eq.7)", NULL, kctx->v4_m4, &kctx->v4_m4, NULL));
    898:   PetscOptionsEnd();
    899:   PetscFunctionReturn(PETSC_SUCCESS);
    900: }

    902: /*@
    903:   SNESSetFromOptions - Sets various `SNES` and `KSP` parameters from user options.

    905:   Collective

    907:   Input Parameter:
    908: . snes - the `SNES` context

    910:   Options Database Keys:
    911: + -snes_type type                                                              - newtonls, newtontr, ngmres, ncg, nrichardson, qn, vi, fas, `SNESType` for complete list
    912: . -snes_rtol rtol                                                              - relative decrease in tolerance norm from initial
    913: . -snes_atol abstol                                                            - absolute tolerance of residual norm
    914: . -snes_stol stol                                                              - convergence tolerance in terms of the norm of the change in the solution between steps
    915: . -snes_divergence_tolerance divtol                                            - if the residual goes above divtol*rnorm0, exit with divergence
    916: . -snes_max_it max_it                                                          - maximum number of iterations
    917: . -snes_max_funcs max_funcs                                                    - maximum number of function evaluations
    918: . -snes_force_iteration force                                                  - force `SNESSolve()` to take at least one iteration
    919: . -snes_max_fail max_fail                                                      - maximum number of line search failures allowed before stopping, default is none
    920: . -snes_max_linear_solve_fail                                                  - number of linear solver failures before SNESSolve() stops
    921: . -snes_lag_preconditioner lag                                                 - how often preconditioner is rebuilt (use -1 to never rebuild)
    922: . -snes_lag_preconditioner_persists (true|false)                               - retains the -snes_lag_preconditioner information across multiple SNESSolve()
    923: . -snes_lag_jacobian lag                                                       - how often Jacobian is rebuilt (use -1 to never rebuild)
    924: . -snes_lag_jacobian_persists (true|false)                                     - retains the -snes_lag_jacobian information across multiple SNESSolve()
    925: . -snes_convergence_test (default|skip|correct_pressure)                       - convergence test in nonlinear solver. default `SNESConvergedDefault()`. skip `SNESConvergedSkip()` means continue
    926:                                                                                  iterating until max_it or some other criterion is reached, saving expense of convergence test. correct_pressure
    927:                                                                                  `SNESConvergedCorrectPressure()` has special handling of a pressure null space.
    928: . -snes_monitor [ascii][:filename][:viewer format]                             - prints residual norm at each iteration. if no filename given prints to stdout
    929: . -snes_monitor_solution [ascii binary draw][:filename][:viewer format]        - plots solution at each iteration
    930: . -snes_monitor_residual [ascii binary draw][:filename][:viewer format]        - plots residual (not its norm) at each iteration
    931: . -snes_monitor_solution_update [ascii binary draw][:filename][:viewer format] - plots update to solution at each iteration
    932: . -snes_monitor draw::draw_lg                                                  - plots residual norm at each iteration
    933: . -snes_monitor_lg_range                                                       - plots function range at each iteration
    934: . -snes_monitor_pause_final                                                    - Pauses all monitor drawing after the solver ends
    935: . -snes_fd                                                                     - use finite differences to compute Jacobian; very slow, only for testing
    936: . -snes_fd_color                                                               - use finite differences with coloring to compute Jacobian
    937: . -snes_mf_ksp_monitor                                                         - if using matrix-free multiply then print h at each `KSP` iteration
    938: . -snes_converged_reason                                                       - print the reason for convergence/divergence after each solve
    939: . -npc_snes_type type                                                          - the `SNES` type to use as a nonlinear preconditioner
    940: . -snes_test_jacobian [threshold]                                              - compare the user provided Jacobian with one computed via finite differences to check for errors.
    941:                                                                                  If a threshold is given, display only those entries whose difference is greater than the threshold.
    942: - -snes_test_jacobian_view                                                     - display the user provided Jacobian, the finite difference Jacobian and the difference between them
    943:                                                                                  to help users detect the location of errors in the user provided Jacobian.

    945:   Options Database Keys for Eisenstat-Walker method:
    946: + -snes_ksp_ew                     - use Eisenstat-Walker method for determining linear system convergence
    947: . -snes_ksp_ew_version ver         - version of  Eisenstat-Walker method
    948: . -snes_ksp_ew_rtol0 rtol0         - Sets rtol0
    949: . -snes_ksp_ew_rtolmax rtolmax     - Sets rtolmax
    950: . -snes_ksp_ew_gamma gamma         - Sets gamma
    951: . -snes_ksp_ew_alpha alpha         - Sets alpha
    952: . -snes_ksp_ew_alpha2 alpha2       - Sets alpha2
    953: - -snes_ksp_ew_threshold threshold - Sets threshold

    955:   Level: beginner

    957:   Notes:
    958:   To see all options, run your program with the -help option or consult the users manual

    960:   `SNES` supports three approaches for computing (approximate) Jacobians: user provided via `SNESSetJacobian()`, matrix-free using `MatCreateSNESMF()`,
    961:   and computing explicitly with
    962:   finite differences and coloring using `MatFDColoring`. It is also possible to use automatic differentiation and the `MatFDColoring` object.

    964: .seealso: [](ch_snes), `SNESType`, `SNESSetOptionsPrefix()`, `SNESResetFromOptions()`, `SNES`, `SNESCreate()`, `MatCreateSNESMF()`, `MatFDColoring`
    965: @*/
    966: PetscErrorCode SNESSetFromOptions(SNES snes)
    967: {
    968:   PetscBool   flg, pcset, persist, set;
    969:   PetscInt    i, indx, lag, grids, max_its, max_funcs;
    970:   const char *deft        = SNESNEWTONLS;
    971:   const char *convtests[] = {"default", "skip", "correct_pressure"};
    972:   SNESKSPEW  *kctx        = NULL;
    973:   char        type[256], monfilename[PETSC_MAX_PATH_LEN], ewprefix[256];
    974:   PCSide      pcside;
    975:   const char *optionsprefix;
    976:   PetscReal   rtol, abstol, stol;

    978:   PetscFunctionBegin;
    980:   PetscCall(SNESRegisterAll());
    981:   PetscObjectOptionsBegin((PetscObject)snes);
    982:   if (((PetscObject)snes)->type_name) deft = ((PetscObject)snes)->type_name;
    983:   PetscCall(PetscOptionsFList("-snes_type", "Nonlinear solver method", "SNESSetType", SNESList, deft, type, 256, &flg));
    984:   if (flg) PetscCall(SNESSetType(snes, type));
    985:   else if (!((PetscObject)snes)->type_name) PetscCall(SNESSetType(snes, deft));

    987:   abstol    = snes->abstol;
    988:   rtol      = snes->rtol;
    989:   stol      = snes->stol;
    990:   max_its   = snes->max_its;
    991:   max_funcs = snes->max_funcs;
    992:   PetscCall(PetscOptionsReal("-snes_rtol", "Stop if decrease in function norm less than", "SNESSetTolerances", snes->rtol, &rtol, NULL));
    993:   PetscCall(PetscOptionsReal("-snes_atol", "Stop if function norm less than", "SNESSetTolerances", snes->abstol, &abstol, NULL));
    994:   PetscCall(PetscOptionsReal("-snes_stol", "Stop if step length less than", "SNESSetTolerances", snes->stol, &stol, NULL));
    995:   PetscCall(PetscOptionsInt("-snes_max_it", "Maximum iterations", "SNESSetTolerances", snes->max_its, &max_its, NULL));
    996:   PetscCall(PetscOptionsInt("-snes_max_funcs", "Maximum function evaluations", "SNESSetTolerances", snes->max_funcs, &max_funcs, NULL));
    997:   PetscCall(SNESSetTolerances(snes, abstol, rtol, stol, max_its, max_funcs));

    999:   PetscCall(PetscOptionsReal("-snes_divergence_tolerance", "Stop if residual norm increases by this factor", "SNESSetDivergenceTolerance", snes->divtol, &snes->divtol, &flg));
    1000:   if (flg) PetscCall(SNESSetDivergenceTolerance(snes, snes->divtol));

    1002:   PetscCall(PetscOptionsInt("-snes_max_fail", "Maximum nonlinear step failures", "SNESSetMaxNonlinearStepFailures", snes->maxFailures, &snes->maxFailures, &flg));
    1003:   if (flg) PetscCall(SNESSetMaxNonlinearStepFailures(snes, snes->maxFailures));

    1005:   PetscCall(PetscOptionsInt("-snes_max_linear_solve_fail", "Maximum failures in linear solves allowed", "SNESSetMaxLinearSolveFailures", snes->maxLinearSolveFailures, &snes->maxLinearSolveFailures, &flg));
    1006:   if (flg) PetscCall(SNESSetMaxLinearSolveFailures(snes, snes->maxLinearSolveFailures));

    1008:   PetscCall(PetscOptionsBool("-snes_error_if_not_converged", "Generate error if solver does not converge", "SNESSetErrorIfNotConverged", snes->errorifnotconverged, &snes->errorifnotconverged, NULL));
    1009:   PetscCall(PetscOptionsBool("-snes_force_iteration", "Force SNESSolve() to take at least one iteration", "SNESSetForceIteration", snes->forceiteration, &snes->forceiteration, NULL));
    1010:   PetscCall(PetscOptionsBool("-snes_check_jacobian_domain_error", "Check Jacobian domain error after Jacobian evaluation", "SNESCheckJacobianDomainError", snes->checkjacdomainerror, &snes->checkjacdomainerror, NULL));

    1012:   PetscCall(PetscOptionsInt("-snes_lag_preconditioner", "How often to rebuild preconditioner", "SNESSetLagPreconditioner", snes->lagpreconditioner, &lag, &flg));
    1013:   if (flg) {
    1014:     PetscCheck(lag != -1, PetscObjectComm((PetscObject)snes), PETSC_ERR_USER, "Cannot set the lag to -1 from the command line since the preconditioner must be built as least once, perhaps you mean -2");
    1015:     PetscCall(SNESSetLagPreconditioner(snes, lag));
    1016:   }
    1017:   PetscCall(PetscOptionsBool("-snes_lag_preconditioner_persists", "Preconditioner lagging through multiple SNES solves", "SNESSetLagPreconditionerPersists", snes->lagjac_persist, &persist, &flg));
    1018:   if (flg) PetscCall(SNESSetLagPreconditionerPersists(snes, persist));
    1019:   PetscCall(PetscOptionsInt("-snes_lag_jacobian", "How often to rebuild Jacobian", "SNESSetLagJacobian", snes->lagjacobian, &lag, &flg));
    1020:   if (flg) {
    1021:     PetscCheck(lag != -1, PetscObjectComm((PetscObject)snes), PETSC_ERR_USER, "Cannot set the lag to -1 from the command line since the Jacobian must be built as least once, perhaps you mean -2");
    1022:     PetscCall(SNESSetLagJacobian(snes, lag));
    1023:   }
    1024:   PetscCall(PetscOptionsBool("-snes_lag_jacobian_persists", "Jacobian lagging through multiple SNES solves", "SNESSetLagJacobianPersists", snes->lagjac_persist, &persist, &flg));
    1025:   if (flg) PetscCall(SNESSetLagJacobianPersists(snes, persist));

    1027:   PetscCall(PetscOptionsInt("-snes_grid_sequence", "Use grid sequencing to generate initial guess", "SNESSetGridSequence", snes->gridsequence, &grids, &flg));
    1028:   if (flg) PetscCall(SNESSetGridSequence(snes, grids));

    1030:   PetscCall(PetscOptionsEList("-snes_convergence_test", "Convergence test", "SNESSetConvergenceTest", convtests, PETSC_STATIC_ARRAY_LENGTH(convtests), "default", &indx, &flg));
    1031:   if (flg) {
    1032:     switch (indx) {
    1033:     case 0:
    1034:       PetscCall(SNESSetConvergenceTest(snes, SNESConvergedDefault, NULL, NULL));
    1035:       break;
    1036:     case 1:
    1037:       PetscCall(SNESSetConvergenceTest(snes, SNESConvergedSkip, NULL, NULL));
    1038:       break;
    1039:     case 2:
    1040:       PetscCall(SNESSetConvergenceTest(snes, SNESConvergedCorrectPressure, NULL, NULL));
    1041:       break;
    1042:     }
    1043:   }

    1045:   PetscCall(PetscOptionsEList("-snes_norm_schedule", "SNES Norm schedule", "SNESSetNormSchedule", SNESNormSchedules, 5, "function", &indx, &flg));
    1046:   if (flg) PetscCall(SNESSetNormSchedule(snes, (SNESNormSchedule)indx));

    1048:   PetscCall(PetscOptionsEList("-snes_function_type", "SNES Norm schedule", "SNESSetFunctionType", SNESFunctionTypes, 2, "unpreconditioned", &indx, &flg));
    1049:   if (flg) PetscCall(SNESSetFunctionType(snes, (SNESFunctionType)indx));

    1051:   kctx = (SNESKSPEW *)snes->kspconvctx;

    1053:   PetscCall(PetscOptionsBool("-snes_ksp_ew", "Use Eisentat-Walker linear system convergence test", "SNESKSPSetUseEW", snes->ksp_ewconv, &snes->ksp_ewconv, NULL));

    1055:   PetscCall(SNESGetOptionsPrefix(snes, &optionsprefix));
    1056:   PetscCall(PetscSNPrintf(ewprefix, sizeof(ewprefix), "%s%s", optionsprefix ? optionsprefix : "", "snes_"));
    1057:   PetscCall(SNESEWSetFromOptions_Private(kctx, PETSC_TRUE, PetscObjectComm((PetscObject)snes), ewprefix));

    1059:   flg = PETSC_FALSE;
    1060:   PetscCall(PetscOptionsBool("-snes_monitor_cancel", "Remove all monitors", "SNESMonitorCancel", flg, &flg, &set));
    1061:   if (set && flg) PetscCall(SNESMonitorCancel(snes));

    1063:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor", "Monitor norm of function", "SNESMonitorDefault", SNESMonitorDefault, SNESMonitorDefaultSetUp));
    1064:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_short", "Monitor norm of function with fewer digits", "SNESMonitorDefaultShort", SNESMonitorDefaultShort, NULL));
    1065:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_range", "Monitor range of elements of function", "SNESMonitorRange", SNESMonitorRange, NULL));

    1067:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_ratio", "Monitor ratios of the norm of function for consecutive steps", "SNESMonitorRatio", SNESMonitorRatio, SNESMonitorRatioSetUp));
    1068:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_field", "Monitor norm of function (split into fields)", "SNESMonitorDefaultField", SNESMonitorDefaultField, NULL));
    1069:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_solution", "View solution at each iteration", "SNESMonitorSolution", SNESMonitorSolution, NULL));
    1070:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_solution_update", "View correction at each iteration", "SNESMonitorSolutionUpdate", SNESMonitorSolutionUpdate, NULL));
    1071:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_residual", "View residual at each iteration", "SNESMonitorResidual", SNESMonitorResidual, NULL));
    1072:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_jacupdate_spectrum", "Print the change in the spectrum of the Jacobian", "SNESMonitorJacUpdateSpectrum", SNESMonitorJacUpdateSpectrum, NULL));
    1073:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_fields", "Monitor norm of function per field", "SNESMonitorSet", SNESMonitorFields, NULL));
    1074:   PetscCall(PetscOptionsBool("-snes_monitor_pause_final", "Pauses all draw monitors at the final iterate", "SNESMonitorPauseFinal_Internal", PETSC_FALSE, &snes->pauseFinal, NULL));

    1076:   PetscCall(PetscOptionsString("-snes_monitor_python", "Use Python function", "SNESMonitorSet", NULL, monfilename, sizeof(monfilename), &flg));
    1077:   if (flg) PetscCall(PetscPythonMonitorSet((PetscObject)snes, monfilename));

    1079:   flg = PETSC_FALSE;
    1080:   PetscCall(PetscOptionsBool("-snes_monitor_lg_range", "Plot function range at each iteration", "SNESMonitorLGRange", flg, &flg, NULL));
    1081:   if (flg) {
    1082:     PetscViewer ctx;

    1084:     PetscCall(PetscViewerDrawOpen(PetscObjectComm((PetscObject)snes), NULL, NULL, PETSC_DECIDE, PETSC_DECIDE, 400, 300, &ctx));
    1085:     PetscCall(SNESMonitorSet(snes, SNESMonitorLGRange, ctx, (PetscCtxDestroyFn *)PetscViewerDestroy));
    1086:   }

    1088:   PetscCall(PetscViewerDestroy(&snes->convergedreasonviewer));
    1089:   PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_converged_reason", &snes->convergedreasonviewer, &snes->convergedreasonformat, NULL));
    1090:   flg = PETSC_FALSE;
    1091:   PetscCall(PetscOptionsBool("-snes_converged_reason_view_cancel", "Remove all converged reason viewers", "SNESConvergedReasonViewCancel", flg, &flg, &set));
    1092:   if (set && flg) PetscCall(SNESConvergedReasonViewCancel(snes));

    1094:   flg = PETSC_FALSE;
    1095:   PetscCall(PetscOptionsBool("-snes_fd", "Use finite differences (slow) to compute Jacobian", "SNESComputeJacobianDefault", flg, &flg, NULL));
    1096:   if (flg) {
    1097:     void *functx;
    1098:     DM    dm;
    1099:     PetscCall(SNESGetDM(snes, &dm));
    1100:     PetscCall(DMSNESUnsetJacobianContext_Internal(dm));
    1101:     PetscCall(SNESGetFunction(snes, NULL, NULL, &functx));
    1102:     PetscCall(SNESSetJacobian(snes, snes->jacobian, snes->jacobian_pre, SNESComputeJacobianDefault, functx));
    1103:     PetscCall(PetscInfo(snes, "Setting default finite difference Jacobian matrix\n"));
    1104:   }

    1106:   flg = PETSC_FALSE;
    1107:   PetscCall(PetscOptionsBool("-snes_fd_function", "Use finite differences (slow) to compute function from user objective", "SNESObjectiveComputeFunctionDefaultFD", flg, &flg, NULL));
    1108:   if (flg) PetscCall(SNESSetFunction(snes, NULL, SNESObjectiveComputeFunctionDefaultFD, NULL));

    1110:   flg = PETSC_FALSE;
    1111:   PetscCall(PetscOptionsBool("-snes_fd_color", "Use finite differences with coloring to compute Jacobian", "SNESComputeJacobianDefaultColor", flg, &flg, NULL));
    1112:   if (flg) {
    1113:     DM dm;
    1114:     PetscCall(SNESGetDM(snes, &dm));
    1115:     PetscCall(DMSNESUnsetJacobianContext_Internal(dm));
    1116:     PetscCall(SNESSetJacobian(snes, snes->jacobian, snes->jacobian_pre, SNESComputeJacobianDefaultColor, NULL));
    1117:     PetscCall(PetscInfo(snes, "Setting default finite difference coloring Jacobian matrix\n"));
    1118:   }

    1120:   flg = PETSC_FALSE;
    1121:   PetscCall(PetscOptionsBool("-snes_mf_operator", "Use a Matrix-Free Jacobian with user-provided matrix for computing the preconditioner", "SNESSetUseMatrixFree", PETSC_FALSE, &snes->mf_operator, &flg));
    1122:   if (flg && snes->mf_operator) {
    1123:     snes->mf_operator = PETSC_TRUE;
    1124:     snes->mf          = PETSC_TRUE;
    1125:   }
    1126:   flg = PETSC_FALSE;
    1127:   PetscCall(PetscOptionsBool("-snes_mf", "Use a Matrix-Free Jacobian with no matrix for computing the preconditioner", "SNESSetUseMatrixFree", PETSC_FALSE, &snes->mf, &flg));
    1128:   if (!flg && snes->mf_operator) snes->mf = PETSC_TRUE;
    1129:   PetscCall(PetscOptionsInt("-snes_mf_version", "Matrix-Free routines version 1 or 2", "None", snes->mf_version, &snes->mf_version, NULL));

    1131:   PetscCall(PetscOptionsName("-snes_test_function", "Compare hand-coded and finite difference functions", "None", &snes->testFunc));
    1132:   PetscCall(PetscOptionsName("-snes_test_jacobian", "Compare hand-coded and finite difference Jacobians", "None", &snes->testJac));

    1134:   flg = PETSC_FALSE;
    1135:   PetscCall(SNESGetNPCSide(snes, &pcside));
    1136:   PetscCall(PetscOptionsEnum("-snes_npc_side", "SNES nonlinear preconditioner side", "SNESSetNPCSide", PCSides, (PetscEnum)pcside, (PetscEnum *)&pcside, &flg));
    1137:   if (flg) PetscCall(SNESSetNPCSide(snes, pcside));

    1139: #if defined(PETSC_HAVE_SAWS)
    1140:   /*
    1141:     Publish convergence information using SAWs
    1142:   */
    1143:   flg = PETSC_FALSE;
    1144:   PetscCall(PetscOptionsBool("-snes_monitor_saws", "Publish SNES progress using SAWs", "SNESMonitorSet", flg, &flg, NULL));
    1145:   if (flg) {
    1146:     PetscCtx ctx;
    1147:     PetscCall(SNESMonitorSAWsCreate(snes, &ctx));
    1148:     PetscCall(SNESMonitorSet(snes, SNESMonitorSAWs, ctx, SNESMonitorSAWsDestroy));
    1149:   }
    1150: #endif
    1151: #if defined(PETSC_HAVE_SAWS)
    1152:   {
    1153:     PetscBool set;
    1154:     flg = PETSC_FALSE;
    1155:     PetscCall(PetscOptionsBool("-snes_saws_block", "Block for SAWs at end of SNESSolve", "PetscObjectSAWsBlock", ((PetscObject)snes)->amspublishblock, &flg, &set));
    1156:     if (set) PetscCall(PetscObjectSAWsSetBlock((PetscObject)snes, flg));
    1157:   }
    1158: #endif

    1160:   for (i = 0; i < numberofsetfromoptions; i++) PetscCall((*othersetfromoptions[i])(snes));

    1162:   PetscTryTypeMethod(snes, setfromoptions, PetscOptionsObject);

    1164:   /* process any options handlers added with PetscObjectAddOptionsHandler() */
    1165:   PetscCall(PetscObjectProcessOptionsHandlers((PetscObject)snes, PetscOptionsObject));
    1166:   PetscOptionsEnd();

    1168:   if (snes->linesearch) {
    1169:     PetscCall(SNESGetLineSearch(snes, &snes->linesearch));
    1170:     PetscCall(SNESLineSearchSetFromOptions(snes->linesearch));
    1171:   }

    1173:   if (snes->usesksp) {
    1174:     if (!snes->ksp) PetscCall(SNESGetKSP(snes, &snes->ksp));
    1175:     PetscCall(KSPSetOperators(snes->ksp, snes->jacobian, snes->jacobian_pre));
    1176:     PetscCall(KSPSetFromOptions(snes->ksp));
    1177:   }

    1179:   /* if user has set the SNES NPC type via options database, create it. */
    1180:   PetscCall(SNESGetOptionsPrefix(snes, &optionsprefix));
    1181:   PetscCall(PetscOptionsHasName(((PetscObject)snes)->options, optionsprefix, "-npc_snes_type", &pcset));
    1182:   if (pcset && (!snes->npc)) PetscCall(SNESGetNPC(snes, &snes->npc));
    1183:   if (snes->npc) PetscCall(SNESSetFromOptions(snes->npc));
    1184:   snes->setfromoptionscalled++;
    1185:   PetscFunctionReturn(PETSC_SUCCESS);
    1186: }

    1188: /*@
    1189:   SNESResetFromOptions - Sets various `SNES` and `KSP` parameters from user options ONLY if the `SNESSetFromOptions()` was previously called

    1191:   Collective

    1193:   Input Parameter:
    1194: . snes - the `SNES` context

    1196:   Level: advanced

    1198: .seealso: [](ch_snes), `SNES`, `SNESSetFromOptions()`, `SNESSetOptionsPrefix()`
    1199: @*/
    1200: PetscErrorCode SNESResetFromOptions(SNES snes)
    1201: {
    1202:   PetscFunctionBegin;
    1203:   if (snes->setfromoptionscalled) PetscCall(SNESSetFromOptions(snes));
    1204:   PetscFunctionReturn(PETSC_SUCCESS);
    1205: }

    1207: /*@C
    1208:   SNESSetComputeApplicationContext - Sets an optional function to compute a user-defined context for
    1209:   the nonlinear solvers.

    1211:   Logically Collective; No Fortran Support

    1213:   Input Parameters:
    1214: + snes    - the `SNES` context
    1215: . compute - function to compute the context
    1216: - destroy - function to destroy the context, see `PetscCtxDestroyFn` for the calling sequence

    1218:   Calling sequence of `compute`:
    1219: + snes - the `SNES` context
    1220: - ctx  - context to be computed

    1222:   Level: intermediate

    1224:   Note:
    1225:   This routine is useful if you are performing grid sequencing or using `SNESFAS` and need the appropriate context generated for each level.

    1227:   Use `SNESSetApplicationContext()` to see the context immediately

    1229: .seealso: [](ch_snes), `SNESGetApplicationContext()`, `SNESSetApplicationContext()`, `PetscCtxDestroyFn`
    1230: @*/
    1231: PetscErrorCode SNESSetComputeApplicationContext(SNES snes, PetscErrorCode (*compute)(SNES snes, PetscCtxRt ctx), PetscCtxDestroyFn *destroy)
    1232: {
    1233:   PetscFunctionBegin;
    1235:   snes->ops->ctxcompute = compute;
    1236:   snes->ops->ctxdestroy = destroy;
    1237:   PetscFunctionReturn(PETSC_SUCCESS);
    1238: }

    1240: /*@
    1241:   SNESSetApplicationContext - Sets the optional user-defined context for the nonlinear solvers.

    1243:   Logically Collective

    1245:   Input Parameters:
    1246: + snes - the `SNES` context
    1247: - ctx  - the application context

    1249:   Level: intermediate

    1251:   Notes:
    1252:   Users can provide a context when constructing the `SNES` options and then access it inside their function, Jacobian computation, or other evaluation function
    1253:   with `SNESGetApplicationContext()`

    1255:   To provide a function that computes the context for you use `SNESSetComputeApplicationContext()`

    1257:   Fortran Note:
    1258:   This only works when `ctx` is a Fortran derived type (it cannot be a `PetscObject`), we recommend writing a Fortran interface definition for this
    1259:   function that tells the Fortran compiler the derived data type that is passed in as the `ctx` argument. See `SNESGetApplicationContext()` for
    1260:   an example.

    1262: .seealso: [](ch_snes), `SNES`, `SNESSetComputeApplicationContext()`, `SNESGetApplicationContext()`
    1263: @*/
    1264: PetscErrorCode SNESSetApplicationContext(SNES snes, PetscCtx ctx)
    1265: {
    1266:   KSP ksp;

    1268:   PetscFunctionBegin;
    1270:   PetscCall(SNESGetKSP(snes, &ksp));
    1271:   PetscCall(KSPSetApplicationContext(ksp, ctx));
    1272:   snes->ctx = ctx;
    1273:   PetscFunctionReturn(PETSC_SUCCESS);
    1274: }

    1276: /*@
    1277:   SNESGetApplicationContext - Gets the user-defined context for the
    1278:   nonlinear solvers set with `SNESGetApplicationContext()` or `SNESSetComputeApplicationContext()`

    1280:   Not Collective

    1282:   Input Parameter:
    1283: . snes - `SNES` context

    1285:   Output Parameter:
    1286: . ctx - the application context

    1288:   Level: intermediate

    1290:   Fortran Notes:
    1291:   This only works when the context is a Fortran derived type or a `PetscObject`. Declare `ctx` with
    1292: .vb
    1293:   type(tUsertype), pointer :: ctx
    1294: .ve

    1296: .seealso: [](ch_snes), `SNESSetApplicationContext()`, `SNESSetComputeApplicationContext()`
    1297: @*/
    1298: PetscErrorCode SNESGetApplicationContext(SNES snes, PetscCtxRt ctx)
    1299: {
    1300:   PetscFunctionBegin;
    1302:   *(void **)ctx = snes->ctx;
    1303:   PetscFunctionReturn(PETSC_SUCCESS);
    1304: }

    1306: /*@
    1307:   SNESSetUseMatrixFree - indicates that `SNES` should use matrix-free finite difference matrix-vector products to apply the Jacobian.

    1309:   Logically Collective

    1311:   Input Parameters:
    1312: + snes        - `SNES` context
    1313: . mf_operator - use matrix-free only for the Amat used by `SNESSetJacobian()`, this means the user provided Pmat will continue to be used
    1314: - mf          - use matrix-free for both the Amat and Pmat used by `SNESSetJacobian()`, both the Amat and Pmat set in `SNESSetJacobian()` will be ignored. With
    1315:                 this option no matrix-element based preconditioners can be used in the linear solve since the matrix won't be explicitly available

    1317:   Options Database Keys:
    1318: + -snes_mf_operator - use matrix-free only for the mat operator
    1319: . -snes_mf          - use matrix-free for both the mat and pmat operator
    1320: . -snes_fd_color    - compute the Jacobian via coloring and finite differences.
    1321: - -snes_fd          - compute the Jacobian via finite differences (slow)

    1323:   Level: intermediate

    1325:   Note:
    1326:   `SNES` supports three approaches for computing (approximate) Jacobians: user provided via `SNESSetJacobian()`, matrix-free using `MatCreateSNESMF()`,
    1327:   and computing explicitly with
    1328:   finite differences and coloring using `MatFDColoring`. It is also possible to use automatic differentiation and the `MatFDColoring` object.

    1330: .seealso: [](ch_snes), `SNES`, `SNESGetUseMatrixFree()`, `MatCreateSNESMF()`, `SNESComputeJacobianDefaultColor()`, `MatFDColoring`
    1331: @*/
    1332: PetscErrorCode SNESSetUseMatrixFree(SNES snes, PetscBool mf_operator, PetscBool mf)
    1333: {
    1334:   PetscFunctionBegin;
    1338:   snes->mf          = mf_operator ? PETSC_TRUE : mf;
    1339:   snes->mf_operator = mf_operator;
    1340:   PetscFunctionReturn(PETSC_SUCCESS);
    1341: }

    1343: /*@
    1344:   SNESGetUseMatrixFree - indicates if the `SNES` uses matrix-free finite difference matrix vector products to apply the Jacobian.

    1346:   Not Collective, but the resulting flags will be the same on all MPI processes

    1348:   Input Parameter:
    1349: . snes - `SNES` context

    1351:   Output Parameters:
    1352: + mf_operator - use matrix-free only for the Amat used by `SNESSetJacobian()`, this means the user provided Pmat will continue to be used
    1353: - mf          - use matrix-free for both the Amat and Pmat used by `SNESSetJacobian()`, both the Amat and Pmat set in `SNESSetJacobian()` will be ignored

    1355:   Level: intermediate

    1357: .seealso: [](ch_snes), `SNES`, `SNESSetUseMatrixFree()`, `MatCreateSNESMF()`
    1358: @*/
    1359: PetscErrorCode SNESGetUseMatrixFree(SNES snes, PetscBool *mf_operator, PetscBool *mf)
    1360: {
    1361:   PetscFunctionBegin;
    1363:   if (mf) *mf = snes->mf;
    1364:   if (mf_operator) *mf_operator = snes->mf_operator;
    1365:   PetscFunctionReturn(PETSC_SUCCESS);
    1366: }

    1368: /*@
    1369:   SNESGetIterationNumber - Gets the number of nonlinear iterations completed in the current or most recent `SNESSolve()`

    1371:   Not Collective

    1373:   Input Parameter:
    1374: . snes - `SNES` context

    1376:   Output Parameter:
    1377: . iter - iteration number

    1379:   Level: intermediate

    1381:   Notes:
    1382:   For example, during the computation of iteration 2 this would return 1.

    1384:   This is useful for using lagged Jacobians (where one does not recompute the
    1385:   Jacobian at each `SNES` iteration). For example, the code
    1386: .vb
    1387:       ierr = SNESGetIterationNumber(snes,&it);
    1388:       if (!(it % 2)) {
    1389:         [compute Jacobian here]
    1390:       }
    1391: .ve
    1392:   can be used in your function that computes the Jacobian to cause the Jacobian to be
    1393:   recomputed every second `SNES` iteration. See also `SNESSetLagJacobian()`

    1395:   After the `SNES` solve is complete this will return the number of nonlinear iterations used.

    1397: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetLagJacobian()`, `SNESGetLinearSolveIterations()`, `SNESSetMonitor()`
    1398: @*/
    1399: PetscErrorCode SNESGetIterationNumber(SNES snes, PetscInt *iter)
    1400: {
    1401:   PetscFunctionBegin;
    1403:   PetscAssertPointer(iter, 2);
    1404:   *iter = snes->iter;
    1405:   PetscFunctionReturn(PETSC_SUCCESS);
    1406: }

    1408: /*@
    1409:   SNESSetIterationNumber - Sets the current iteration number.

    1411:   Not Collective

    1413:   Input Parameters:
    1414: + snes - `SNES` context
    1415: - iter - iteration number

    1417:   Level: developer

    1419:   Note:
    1420:   This should only be called inside a `SNES` nonlinear solver.

    1422: .seealso: [](ch_snes), `SNESGetLinearSolveIterations()`
    1423: @*/
    1424: PetscErrorCode SNESSetIterationNumber(SNES snes, PetscInt iter)
    1425: {
    1426:   PetscFunctionBegin;
    1428:   PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
    1429:   snes->iter = iter;
    1430:   PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
    1431:   PetscFunctionReturn(PETSC_SUCCESS);
    1432: }

    1434: /*@
    1435:   SNESGetNonlinearStepFailures - Gets the number of unsuccessful steps
    1436:   taken by the nonlinear solver in the current or most recent `SNESSolve()` .

    1438:   Not Collective

    1440:   Input Parameter:
    1441: . snes - `SNES` context

    1443:   Output Parameter:
    1444: . nfails - number of unsuccessful steps attempted

    1446:   Level: intermediate

    1448:   Notes:
    1449:   A failed step is a step that was generated and taken but did not satisfy the requested step criteria. For example,
    1450:   the `SNESLineSearchApply()` could not generate a sufficient decrease in the function norm (in fact it may have produced an increase).

    1452:   Taken steps that produce a infinity or NaN in the function evaluation or generate a `SNESSetFunctionDomainError()`
    1453:   will always immediately terminate the `SNESSolve()` regardless of the value of `maxFails`.

    1455:   `SNESSetMaxNonlinearStepFailures()` determines how many unsuccessful steps are allowed before the `SNESSolve()` terminates

    1457:   This counter is reset to zero for each successive call to `SNESSolve()`.

    1459: .seealso: [](ch_snes), `SNES`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`, `SNESGetLinearSolveFailures()`,
    1460:           `SNESSetMaxNonlinearStepFailures()`, `SNESGetMaxNonlinearStepFailures()`
    1461: @*/
    1462: PetscErrorCode SNESGetNonlinearStepFailures(SNES snes, PetscInt *nfails)
    1463: {
    1464:   PetscFunctionBegin;
    1466:   PetscAssertPointer(nfails, 2);
    1467:   *nfails = snes->numFailures;
    1468:   PetscFunctionReturn(PETSC_SUCCESS);
    1469: }

    1471: /*@
    1472:   SNESSetMaxNonlinearStepFailures - Sets the maximum number of unsuccessful steps
    1473:   attempted by the nonlinear solver before it gives up and returns unconverged or generates an error

    1475:   Not Collective

    1477:   Input Parameters:
    1478: + snes     - `SNES` context
    1479: - maxFails - maximum of unsuccessful steps allowed, use `PETSC_UNLIMITED` to have no limit on the number of failures

    1481:   Options Database Key:
    1482: . -snes_max_fail n - maximum number of unsuccessful steps allowed

    1484:   Level: intermediate

    1486:   Note:
    1487:   A failed step is a step that was generated and taken but did not satisfy the requested criteria. For example,
    1488:   the `SNESLineSearchApply()` could not generate a sufficient decrease in the function norm (in fact it may have produced an increase).

    1490:   Taken steps that produce a infinity or NaN in the function evaluation or generate a `SNESSetFunctionDomainError()`
    1491:   will always immediately terminate the `SNESSolve()` regardless of the value of `maxFails`.

    1493:   Developer Note:
    1494:   The options database key is wrong for this function name

    1496: .seealso: [](ch_snes), `SNESSetErrorIfNotConverged()`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`,
    1497:           `SNESGetLinearSolveFailures()`, `SNESGetMaxNonlinearStepFailures()`, `SNESGetNonlinearStepFailures()`, `SNESCheckLineSearchFailure()`
    1498: @*/
    1499: PetscErrorCode SNESSetMaxNonlinearStepFailures(SNES snes, PetscInt maxFails)
    1500: {
    1501:   PetscFunctionBegin;

    1504:   if (maxFails == PETSC_UNLIMITED) {
    1505:     snes->maxFailures = PETSC_INT_MAX;
    1506:   } else {
    1507:     PetscCheck(maxFails >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Cannot have a negative maximum number of failures");
    1508:     snes->maxFailures = maxFails;
    1509:   }
    1510:   PetscFunctionReturn(PETSC_SUCCESS);
    1511: }

    1513: /*@
    1514:   SNESGetMaxNonlinearStepFailures - Gets the maximum number of unsuccessful steps
    1515:   attempted by the nonlinear solver before it gives up and returns unconverged or generates an error

    1517:   Not Collective

    1519:   Input Parameter:
    1520: . snes - `SNES` context

    1522:   Output Parameter:
    1523: . maxFails - maximum of unsuccessful steps

    1525:   Level: intermediate

    1527: .seealso: [](ch_snes), `SNESSetErrorIfNotConverged()`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`, `SNESGetLinearSolveFailures()`,
    1528:           `SNESSetMaxNonlinearStepFailures()`, `SNESGetNonlinearStepFailures()`
    1529: @*/
    1530: PetscErrorCode SNESGetMaxNonlinearStepFailures(SNES snes, PetscInt *maxFails)
    1531: {
    1532:   PetscFunctionBegin;
    1534:   PetscAssertPointer(maxFails, 2);
    1535:   *maxFails = snes->maxFailures;
    1536:   PetscFunctionReturn(PETSC_SUCCESS);
    1537: }

    1539: /*@
    1540:   SNESGetNumberFunctionEvals - Gets the number of user provided function evaluations
    1541:   done by the `SNES` object in the current or most recent `SNESSolve()`

    1543:   Not Collective

    1545:   Input Parameter:
    1546: . snes - `SNES` context

    1548:   Output Parameter:
    1549: . nfuncs - number of evaluations

    1551:   Level: intermediate

    1553:   Note:
    1554:   Reset every time `SNESSolve()` is called unless `SNESSetCountersReset()` is used.

    1556: .seealso: [](ch_snes), `SNES`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`, `SNESGetLinearSolveFailures()`, `SNESSetCountersReset()`
    1557: @*/
    1558: PetscErrorCode SNESGetNumberFunctionEvals(SNES snes, PetscInt *nfuncs)
    1559: {
    1560:   PetscFunctionBegin;
    1562:   PetscAssertPointer(nfuncs, 2);
    1563:   *nfuncs = snes->nfuncs;
    1564:   PetscFunctionReturn(PETSC_SUCCESS);
    1565: }

    1567: /*@
    1568:   SNESGetLinearSolveFailures - Gets the number of failed (non-converged)
    1569:   linear solvers in the current or most recent `SNESSolve()`

    1571:   Not Collective

    1573:   Input Parameter:
    1574: . snes - `SNES` context

    1576:   Output Parameter:
    1577: . nfails - number of failed solves

    1579:   Options Database Key:
    1580: . -snes_max_linear_solve_fail num - The number of failures before the solve is terminated

    1582:   Level: intermediate

    1584:   Note:
    1585:   This counter is reset to zero for each successive call to `SNESSolve()`.

    1587: .seealso: [](ch_snes), `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`
    1588: @*/
    1589: PetscErrorCode SNESGetLinearSolveFailures(SNES snes, PetscInt *nfails)
    1590: {
    1591:   PetscFunctionBegin;
    1593:   PetscAssertPointer(nfails, 2);
    1594:   *nfails = snes->numLinearSolveFailures;
    1595:   PetscFunctionReturn(PETSC_SUCCESS);
    1596: }

    1598: /*@
    1599:   SNESSetMaxLinearSolveFailures - the number of failed linear solve attempts
    1600:   allowed before `SNES` returns with a diverged reason of `SNES_DIVERGED_LINEAR_SOLVE`

    1602:   Logically Collective

    1604:   Input Parameters:
    1605: + snes     - `SNES` context
    1606: - maxFails - maximum allowed linear solve failures, use `PETSC_UNLIMITED` to have no limit on the number of failures

    1608:   Options Database Key:
    1609: . -snes_max_linear_solve_fail num - The number of failures before the solve is terminated

    1611:   Level: intermediate

    1613:   Note:
    1614:   By default this is 0; that is `SNES` returns on the first failed linear solve

    1616:   Developer Note:
    1617:   The options database key is wrong for this function name

    1619: .seealso: [](ch_snes), `SNESSetErrorIfNotConverged()`, `SNESGetLinearSolveFailures()`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`
    1620: @*/
    1621: PetscErrorCode SNESSetMaxLinearSolveFailures(SNES snes, PetscInt maxFails)
    1622: {
    1623:   PetscFunctionBegin;

    1627:   if (maxFails == PETSC_UNLIMITED) {
    1628:     snes->maxLinearSolveFailures = PETSC_INT_MAX;
    1629:   } else {
    1630:     PetscCheck(maxFails >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Cannot have a negative maximum number of failures");
    1631:     snes->maxLinearSolveFailures = maxFails;
    1632:   }
    1633:   PetscFunctionReturn(PETSC_SUCCESS);
    1634: }

    1636: /*@
    1637:   SNESGetMaxLinearSolveFailures - gets the maximum number of linear solve failures that
    1638:   are allowed before `SNES` returns as unsuccessful

    1640:   Not Collective

    1642:   Input Parameter:
    1643: . snes - `SNES` context

    1645:   Output Parameter:
    1646: . maxFails - maximum of unsuccessful solves allowed

    1648:   Level: intermediate

    1650:   Note:
    1651:   By default this is 1; that is `SNES` returns on the first failed linear solve

    1653: .seealso: [](ch_snes), `SNESSetErrorIfNotConverged()`, `SNESGetLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`
    1654: @*/
    1655: PetscErrorCode SNESGetMaxLinearSolveFailures(SNES snes, PetscInt *maxFails)
    1656: {
    1657:   PetscFunctionBegin;
    1659:   PetscAssertPointer(maxFails, 2);
    1660:   *maxFails = snes->maxLinearSolveFailures;
    1661:   PetscFunctionReturn(PETSC_SUCCESS);
    1662: }

    1664: /*@
    1665:   SNESGetLinearSolveIterations - Gets the total number of linear iterations
    1666:   used by the nonlinear solver in the most recent `SNESSolve()`

    1668:   Not Collective

    1670:   Input Parameter:
    1671: . snes - `SNES` context

    1673:   Output Parameter:
    1674: . lits - number of linear iterations

    1676:   Level: intermediate

    1678:   Notes:
    1679:   This counter is reset to zero for each successive call to `SNESSolve()` unless `SNESSetCountersReset()` is used.

    1681:   If the linear solver fails inside the `SNESSolve()` the iterations for that call to the linear solver are not included. If you wish to count them
    1682:   then call `KSPGetIterationNumber()` after the failed solve.

    1684: .seealso: [](ch_snes), `SNES`, `SNESGetIterationNumber()`, `SNESGetLinearSolveFailures()`, `SNESGetMaxLinearSolveFailures()`, `SNESSetCountersReset()`
    1685: @*/
    1686: PetscErrorCode SNESGetLinearSolveIterations(SNES snes, PetscInt *lits)
    1687: {
    1688:   PetscFunctionBegin;
    1690:   PetscAssertPointer(lits, 2);
    1691:   *lits = snes->linear_its;
    1692:   PetscFunctionReturn(PETSC_SUCCESS);
    1693: }

    1695: /*@
    1696:   SNESSetCountersReset - Sets whether or not the counters for linear iterations and function evaluations
    1697:   are reset every time `SNESSolve()` is called.

    1699:   Logically Collective

    1701:   Input Parameters:
    1702: + snes  - `SNES` context
    1703: - reset - whether to reset the counters or not, defaults to `PETSC_TRUE`

    1705:   Level: developer

    1707: .seealso: [](ch_snes), `SNESGetNumberFunctionEvals()`, `SNESGetLinearSolveIterations()`, `SNESGetNPC()`
    1708: @*/
    1709: PetscErrorCode SNESSetCountersReset(SNES snes, PetscBool reset)
    1710: {
    1711:   PetscFunctionBegin;
    1714:   snes->counters_reset = reset;
    1715:   PetscFunctionReturn(PETSC_SUCCESS);
    1716: }

    1718: /*@
    1719:   SNESResetCounters - Reset counters for linear iterations and function evaluations.

    1721:   Logically Collective

    1723:   Input Parameters:
    1724: . snes - `SNES` context

    1726:   Level: developer

    1728:   Note:
    1729:   It honors the flag set with `SNESSetCountersReset()`

    1731: .seealso: [](ch_snes), `SNESGetNumberFunctionEvals()`, `SNESGetLinearSolveIterations()`, `SNESGetNPC()`
    1732: @*/
    1733: PetscErrorCode SNESResetCounters(SNES snes)
    1734: {
    1735:   PetscFunctionBegin;
    1737:   if (snes->counters_reset) {
    1738:     snes->nfuncs      = 0;
    1739:     snes->linear_its  = 0;
    1740:     snes->numFailures = 0;
    1741:   }
    1742:   PetscFunctionReturn(PETSC_SUCCESS);
    1743: }

    1745: /*@
    1746:   SNESSetKSP - Sets a `KSP` context for the `SNES` object to use

    1748:   Not Collective, but the `SNES` and `KSP` objects must live on the same `MPI_Comm`

    1750:   Input Parameters:
    1751: + snes - the `SNES` context
    1752: - ksp  - the `KSP` context

    1754:   Level: developer

    1756:   Notes:
    1757:   The `SNES` object already has its `KSP` object, you can obtain with `SNESGetKSP()`
    1758:   so this routine is rarely needed.

    1760:   The `KSP` object that is already in the `SNES` object has its reference count
    1761:   decreased by one when this is called.

    1763: .seealso: [](ch_snes), `SNES`, `KSP`, `KSPGetPC()`, `SNESCreate()`, `KSPCreate()`
    1764: @*/
    1765: PetscErrorCode SNESSetKSP(SNES snes, KSP ksp)
    1766: {
    1767:   PetscFunctionBegin;
    1770:   PetscCheckSameComm(snes, 1, ksp, 2);
    1771:   PetscCall(PetscObjectReference((PetscObject)ksp));
    1772:   PetscCall(PetscObjectDereference((PetscObject)snes->ksp));
    1773:   snes->ksp = ksp;
    1774:   PetscFunctionReturn(PETSC_SUCCESS);
    1775: }

    1777: /*@
    1778:   SNESParametersInitialize - Sets all the parameters in `snes` to their default value (when `SNESCreate()` was called) if they
    1779:   currently contain default values

    1781:   Collective

    1783:   Input Parameter:
    1784: . snes - the `SNES` object

    1786:   Level: developer

    1788:   Developer Note:
    1789:   This is called by all the `SNESCreate_XXX()` routines.

    1791: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESDestroy()`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobian()`,
    1792:           `PetscObjectParameterSetDefault()`
    1793: @*/
    1794: PetscErrorCode SNESParametersInitialize(SNES snes)
    1795: {
    1796:   PetscObjectParameterSetDefault(snes, max_its, 50);
    1797:   PetscObjectParameterSetDefault(snes, max_funcs, 10000);
    1798:   PetscObjectParameterSetDefault(snes, rtol, PetscDefined(USE_REAL_SINGLE) ? 1.e-5 : 1.e-8);
    1799:   PetscObjectParameterSetDefault(snes, abstol, PetscDefined(USE_REAL_SINGLE) ? 1.e-25 : 1.e-50);
    1800:   PetscObjectParameterSetDefault(snes, stol, PetscDefined(USE_REAL_SINGLE) ? 1.e-5 : 1.e-8);
    1801:   PetscObjectParameterSetDefault(snes, divtol, 1.e4);
    1802:   return PETSC_SUCCESS;
    1803: }

    1805: /*@
    1806:   SNESCreate - Creates a nonlinear solver context used to manage a set of nonlinear solves

    1808:   Collective

    1810:   Input Parameter:
    1811: . comm - MPI communicator

    1813:   Output Parameter:
    1814: . outsnes - the new `SNES` context

    1816:   Options Database Keys:
    1817: + -snes_mf          - Activates default matrix-free Jacobian-vector products, and no matrix to construct a preconditioner
    1818: . -snes_mf_operator - Activates default matrix-free Jacobian-vector products, and a user-provided matrix as set by `SNESSetJacobian()`
    1819: . -snes_fd_coloring - uses a relative fast computation of the Jacobian using finite differences and a graph coloring
    1820: - -snes_fd          - Uses (slow!) finite differences to compute Jacobian

    1822:   Level: beginner

    1824:   Developer Notes:
    1825:   `SNES` always creates a `KSP` object even though many `SNES` methods do not use it. This is
    1826:   unfortunate and should be fixed at some point. The flag snes->usesksp indicates if the
    1827:   particular method does use `KSP` and regulates if the information about the `KSP` is printed
    1828:   in `SNESView()`.

    1830:   `TSSetFromOptions()` does call `SNESSetFromOptions()` which can lead to users being confused
    1831:   by help messages about meaningless `SNES` options.

    1833:   `SNES` always creates the `snes->kspconvctx` even though it is used by only one type. This should be fixed.

    1835: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESDestroy()`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobian()`
    1836: @*/
    1837: PetscErrorCode SNESCreate(MPI_Comm comm, SNES *outsnes)
    1838: {
    1839:   SNES       snes;
    1840:   SNESKSPEW *kctx;

    1842:   PetscFunctionBegin;
    1843:   PetscAssertPointer(outsnes, 2);
    1844:   PetscCall(SNESInitializePackage());

    1846:   PetscCall(PetscHeaderCreate(snes, SNES_CLASSID, "SNES", "Nonlinear solver", "SNES", comm, SNESDestroy, SNESView));
    1847:   snes->ops->converged = SNESConvergedDefault;
    1848:   snes->usesksp        = PETSC_TRUE;
    1849:   snes->norm           = 0.0;
    1850:   snes->xnorm          = 0.0;
    1851:   snes->ynorm          = 0.0;
    1852:   snes->normschedule   = SNES_NORM_ALWAYS;
    1853:   snes->functype       = SNES_FUNCTION_DEFAULT;
    1854:   snes->ttol           = 0.0;

    1856:   snes->rnorm0               = 0;
    1857:   snes->nfuncs               = 0;
    1858:   snes->numFailures          = 0;
    1859:   snes->maxFailures          = 1;
    1860:   snes->linear_its           = 0;
    1861:   snes->lagjacobian          = 1;
    1862:   snes->jac_iter             = 0;
    1863:   snes->lagjac_persist       = PETSC_FALSE;
    1864:   snes->lagpreconditioner    = 1;
    1865:   snes->pre_iter             = 0;
    1866:   snes->lagpre_persist       = PETSC_FALSE;
    1867:   snes->numbermonitors       = 0;
    1868:   snes->numberreasonviews    = 0;
    1869:   snes->data                 = NULL;
    1870:   snes->setupcalled          = PETSC_FALSE;
    1871:   snes->ksp_ewconv           = PETSC_FALSE;
    1872:   snes->nwork                = 0;
    1873:   snes->work                 = NULL;
    1874:   snes->nvwork               = 0;
    1875:   snes->vwork                = NULL;
    1876:   snes->conv_hist_len        = 0;
    1877:   snes->conv_hist_max        = 0;
    1878:   snes->conv_hist            = NULL;
    1879:   snes->conv_hist_its        = NULL;
    1880:   snes->conv_hist_reset      = PETSC_TRUE;
    1881:   snes->counters_reset       = PETSC_TRUE;
    1882:   snes->vec_func_init_set    = PETSC_FALSE;
    1883:   snes->reason               = SNES_CONVERGED_ITERATING;
    1884:   snes->npcside              = PC_RIGHT;
    1885:   snes->setfromoptionscalled = 0;

    1887:   snes->mf          = PETSC_FALSE;
    1888:   snes->mf_operator = PETSC_FALSE;
    1889:   snes->mf_version  = 1;

    1891:   snes->numLinearSolveFailures = 0;
    1892:   snes->maxLinearSolveFailures = 1;

    1894:   snes->vizerotolerance     = 1.e-8;
    1895:   snes->checkjacdomainerror = PetscDefined(USE_DEBUG) ? PETSC_TRUE : PETSC_FALSE;

    1897:   /* Set this to true if the implementation of SNESSolve_XXX does compute the residual at the final solution. */
    1898:   snes->alwayscomputesfinalresidual = PETSC_FALSE;

    1900:   /* Create context to compute Eisenstat-Walker relative tolerance for KSP */
    1901:   PetscCall(PetscNew(&kctx));

    1903:   snes->kspconvctx  = kctx;
    1904:   kctx->version     = 2;
    1905:   kctx->rtol_0      = 0.3; /* Eisenstat and Walker suggest rtol_0=.5, but
    1906:                              this was too large for some test cases */
    1907:   kctx->rtol_last   = 0.0;
    1908:   kctx->rtol_max    = 0.9;
    1909:   kctx->gamma       = 1.0;
    1910:   kctx->alpha       = 0.5 * (1.0 + PetscSqrtReal(5.0));
    1911:   kctx->alpha2      = kctx->alpha;
    1912:   kctx->threshold   = 0.1;
    1913:   kctx->lresid_last = 0.0;
    1914:   kctx->norm_last   = 0.0;

    1916:   kctx->rk_last     = 0.0;
    1917:   kctx->rk_last_2   = 0.0;
    1918:   kctx->rtol_last_2 = 0.0;
    1919:   kctx->v4_p1       = 0.1;
    1920:   kctx->v4_p2       = 0.4;
    1921:   kctx->v4_p3       = 0.7;
    1922:   kctx->v4_m1       = 0.8;
    1923:   kctx->v4_m2       = 0.5;
    1924:   kctx->v4_m3       = 0.1;
    1925:   kctx->v4_m4       = 0.5;

    1927:   PetscCall(SNESParametersInitialize(snes));
    1928:   *outsnes = snes;
    1929:   PetscFunctionReturn(PETSC_SUCCESS);
    1930: }

    1932: /*@C
    1933:   SNESSetFunction - Sets the function evaluation routine and function
    1934:   vector for use by the `SNES` routines in solving systems of nonlinear
    1935:   equations.

    1937:   Logically Collective

    1939:   Input Parameters:
    1940: + snes - the `SNES` context
    1941: . r    - vector to store function values, may be `NULL`
    1942: . f    - function evaluation routine;  for calling sequence see `SNESFunctionFn`
    1943: - ctx  - [optional] user-defined context for private data for the
    1944:          function evaluation routine (may be `NULL`)

    1946:   Level: beginner

    1948: .seealso: [](ch_snes), `SNES`, `SNESGetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESSetPicard()`, `SNESFunctionFn`
    1949: @*/
    1950: PetscErrorCode SNESSetFunction(SNES snes, Vec r, SNESFunctionFn *f, PetscCtx ctx)
    1951: {
    1952:   DM dm;

    1954:   PetscFunctionBegin;
    1956:   if (r) {
    1958:     PetscCheckSameComm(snes, 1, r, 2);
    1959:     PetscCall(PetscObjectReference((PetscObject)r));
    1960:     PetscCall(VecDestroy(&snes->vec_func));
    1961:     snes->vec_func = r;
    1962:   }
    1963:   PetscCall(SNESGetDM(snes, &dm));
    1964:   PetscCall(DMSNESSetFunction(dm, f, ctx));
    1965:   if (f == SNESPicardComputeFunction) PetscCall(DMSNESSetMFFunction(dm, SNESPicardComputeMFFunction, ctx));
    1966:   PetscFunctionReturn(PETSC_SUCCESS);
    1967: }

    1969: /*@C
    1970:   SNESSetInitialFunction - Set an already computed function evaluation at the initial guess to be reused by `SNESSolve()`.

    1972:   Logically Collective

    1974:   Input Parameters:
    1975: + snes - the `SNES` context
    1976: - f    - vector to store function value

    1978:   Level: developer

    1980:   Notes:
    1981:   This should not be modified during the solution procedure.

    1983:   This is used extensively in the `SNESFAS` hierarchy and in nonlinear preconditioning.

    1985: .seealso: [](ch_snes), `SNES`, `SNESFAS`, `SNESSetFunction()`, `SNESComputeFunction()`, `SNESSetInitialFunctionNorm()`
    1986: @*/
    1987: PetscErrorCode SNESSetInitialFunction(SNES snes, Vec f)
    1988: {
    1989:   Vec vec_func;

    1991:   PetscFunctionBegin;
    1994:   PetscCheckSameComm(snes, 1, f, 2);
    1995:   if (snes->npcside == PC_LEFT && snes->functype == SNES_FUNCTION_PRECONDITIONED) {
    1996:     snes->vec_func_init_set = PETSC_FALSE;
    1997:     PetscFunctionReturn(PETSC_SUCCESS);
    1998:   }
    1999:   PetscCall(SNESGetFunction(snes, &vec_func, NULL, NULL));
    2000:   PetscCall(VecCopy(f, vec_func));

    2002:   snes->vec_func_init_set = PETSC_TRUE;
    2003:   PetscFunctionReturn(PETSC_SUCCESS);
    2004: }

    2006: /*@
    2007:   SNESSetNormSchedule - Sets the `SNESNormSchedule` used in convergence and monitoring
    2008:   of the `SNES` method, when norms are computed in the solving process

    2010:   Logically Collective

    2012:   Input Parameters:
    2013: + snes         - the `SNES` context
    2014: - normschedule - the frequency of norm computation

    2016:   Options Database Key:
    2017: . -snes_norm_schedule (none|always|initialonly|finalonly|initialfinalonly) - set the schedule

    2019:   Level: advanced

    2021:   Notes:
    2022:   Only certain `SNES` methods support certain `SNESNormSchedules`.  Most require evaluation
    2023:   of the nonlinear function and the taking of its norm at every iteration to
    2024:   even ensure convergence at all.  However, methods such as custom Gauss-Seidel methods
    2025:   `SNESNGS` and the like do not require the norm of the function to be computed, and therefore
    2026:   may either be monitored for convergence or not.  As these are often used as nonlinear
    2027:   preconditioners, monitoring the norm of their error is not a useful enterprise within
    2028:   their solution.

    2030: .seealso: [](ch_snes), `SNESNormSchedule`, `SNESGetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`
    2031: @*/
    2032: PetscErrorCode SNESSetNormSchedule(SNES snes, SNESNormSchedule normschedule)
    2033: {
    2034:   PetscFunctionBegin;
    2036:   snes->normschedule = normschedule;
    2037:   PetscFunctionReturn(PETSC_SUCCESS);
    2038: }

    2040: /*@
    2041:   SNESGetNormSchedule - Gets the `SNESNormSchedule` used in convergence and monitoring
    2042:   of the `SNES` method.

    2044:   Logically Collective

    2046:   Input Parameters:
    2047: + snes         - the `SNES` context
    2048: - normschedule - the type of the norm used

    2050:   Level: advanced

    2052: .seealso: [](ch_snes), `SNES`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2053: @*/
    2054: PetscErrorCode SNESGetNormSchedule(SNES snes, SNESNormSchedule *normschedule)
    2055: {
    2056:   PetscFunctionBegin;
    2058:   *normschedule = snes->normschedule;
    2059:   PetscFunctionReturn(PETSC_SUCCESS);
    2060: }

    2062: /*@
    2063:   SNESSetFunctionNorm - Sets the last computed residual norm.

    2065:   Logically Collective

    2067:   Input Parameters:
    2068: + snes - the `SNES` context
    2069: - norm - the value of the norm

    2071:   Level: developer

    2073: .seealso: [](ch_snes), `SNES`, `SNESGetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2074: @*/
    2075: PetscErrorCode SNESSetFunctionNorm(SNES snes, PetscReal norm)
    2076: {
    2077:   PetscFunctionBegin;
    2079:   snes->norm = norm;
    2080:   PetscFunctionReturn(PETSC_SUCCESS);
    2081: }

    2083: /*@
    2084:   SNESGetFunctionNorm - Gets the last computed norm of the residual

    2086:   Not Collective

    2088:   Input Parameter:
    2089: . snes - the `SNES` context

    2091:   Output Parameter:
    2092: . norm - the last computed residual norm

    2094:   Level: developer

    2096: .seealso: [](ch_snes), `SNES`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2097: @*/
    2098: PetscErrorCode SNESGetFunctionNorm(SNES snes, PetscReal *norm)
    2099: {
    2100:   PetscFunctionBegin;
    2102:   PetscAssertPointer(norm, 2);
    2103:   *norm = snes->norm;
    2104:   PetscFunctionReturn(PETSC_SUCCESS);
    2105: }

    2107: /*@
    2108:   SNESGetUpdateNorm - Gets the last computed norm of the solution update

    2110:   Not Collective

    2112:   Input Parameter:
    2113: . snes - the `SNES` context

    2115:   Output Parameter:
    2116: . ynorm - the last computed update norm

    2118:   Level: developer

    2120:   Note:
    2121:   The new solution is the current solution plus the update, so this norm is an indication of the size of the update

    2123: .seealso: [](ch_snes), `SNES`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `SNESGetFunctionNorm()`
    2124: @*/
    2125: PetscErrorCode SNESGetUpdateNorm(SNES snes, PetscReal *ynorm)
    2126: {
    2127:   PetscFunctionBegin;
    2129:   PetscAssertPointer(ynorm, 2);
    2130:   *ynorm = snes->ynorm;
    2131:   PetscFunctionReturn(PETSC_SUCCESS);
    2132: }

    2134: /*@
    2135:   SNESGetSolutionNorm - Gets the last computed norm of the solution

    2137:   Not Collective

    2139:   Input Parameter:
    2140: . snes - the `SNES` context

    2142:   Output Parameter:
    2143: . xnorm - the last computed solution norm

    2145:   Level: developer

    2147: .seealso: [](ch_snes), `SNES`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `SNESGetFunctionNorm()`, `SNESGetUpdateNorm()`
    2148: @*/
    2149: PetscErrorCode SNESGetSolutionNorm(SNES snes, PetscReal *xnorm)
    2150: {
    2151:   PetscFunctionBegin;
    2153:   PetscAssertPointer(xnorm, 2);
    2154:   *xnorm = snes->xnorm;
    2155:   PetscFunctionReturn(PETSC_SUCCESS);
    2156: }

    2158: /*@
    2159:   SNESSetFunctionType - Sets the `SNESFunctionType`
    2160:   of the `SNES` method.

    2162:   Logically Collective

    2164:   Input Parameters:
    2165: + snes - the `SNES` context
    2166: - type - the function type

    2168:   Level: developer

    2170:   Values of the function type\:
    2171: +  `SNES_FUNCTION_DEFAULT`          - the default for the given `SNESType`
    2172: .  `SNES_FUNCTION_UNPRECONDITIONED` - an unpreconditioned function evaluation (this is the function provided with `SNESSetFunction()`
    2173: -  `SNES_FUNCTION_PRECONDITIONED`   - a transformation of the function provided with `SNESSetFunction()`

    2175:   Note:
    2176:   Different `SNESType`s use this value in different ways

    2178: .seealso: [](ch_snes), `SNES`, `SNESFunctionType`, `SNESGetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2179: @*/
    2180: PetscErrorCode SNESSetFunctionType(SNES snes, SNESFunctionType type)
    2181: {
    2182:   PetscFunctionBegin;
    2184:   snes->functype = type;
    2185:   PetscFunctionReturn(PETSC_SUCCESS);
    2186: }

    2188: /*@
    2189:   SNESGetFunctionType - Gets the `SNESFunctionType` used in convergence and monitoring set with `SNESSetFunctionType()`
    2190:   of the SNES method.

    2192:   Logically Collective

    2194:   Input Parameters:
    2195: + snes - the `SNES` context
    2196: - type - the type of the function evaluation, see `SNESSetFunctionType()`

    2198:   Level: advanced

    2200: .seealso: [](ch_snes), `SNESSetFunctionType()`, `SNESFunctionType`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2201: @*/
    2202: PetscErrorCode SNESGetFunctionType(SNES snes, SNESFunctionType *type)
    2203: {
    2204:   PetscFunctionBegin;
    2206:   *type = snes->functype;
    2207:   PetscFunctionReturn(PETSC_SUCCESS);
    2208: }

    2210: /*@C
    2211:   SNESSetNGS - Sets the user nonlinear Gauss-Seidel routine for
    2212:   use with composed nonlinear solvers.

    2214:   Input Parameters:
    2215: + snes - the `SNES` context, usually of the `SNESType` `SNESNGS`
    2216: . f    - function evaluation routine to apply Gauss-Seidel, see `SNESNGSFn` for calling sequence
    2217: - ctx  - [optional] user-defined context for private data for the smoother evaluation routine (may be `NULL`)

    2219:   Level: intermediate

    2221:   Note:
    2222:   The `SNESNGS` routines are used by the composed nonlinear solver to generate
    2223:   a problem appropriate update to the solution, particularly `SNESFAS`.

    2225: .seealso: [](ch_snes), `SNESNGS`, `SNESGetNGS()`, `SNESNCG`, `SNESGetFunction()`, `SNESComputeNGS()`, `SNESNGSFn`
    2226: @*/
    2227: PetscErrorCode SNESSetNGS(SNES snes, SNESNGSFn *f, PetscCtx ctx)
    2228: {
    2229:   DM dm;

    2231:   PetscFunctionBegin;
    2233:   PetscCall(SNESGetDM(snes, &dm));
    2234:   PetscCall(DMSNESSetNGS(dm, f, ctx));
    2235:   PetscFunctionReturn(PETSC_SUCCESS);
    2236: }

    2238: /*@C
    2239:   SNESPicardComputeMFFunction - Matrix-free residual $A(x) x - b(x)$ used by `SNESSetPicard()` when the operator is applied through `-snes_mf_operator`

    2241:   Collective

    2243:   Input Parameters:
    2244: + snes - the `SNES` context
    2245: . x    - the current iterate
    2246: - ctx  - unused application context; the Picard callbacks are retrieved from the attached `DMSNES`

    2248:   Output Parameter:
    2249: . f - the residual vector

    2251:   Level: developer

    2253:   Note:
    2254:   Uses a duplicate of `snes->jacobian_pre` because `snes->jacobian_pre` cannot be changed during the `KSPSolve()`.

    2256: .seealso: [](ch_snes), `SNES`, `SNESSetPicard()`, `SNESPicardComputeFunction()`, `SNESPicardComputeJacobian()`
    2257: @*/
    2258: PetscErrorCode SNESPicardComputeMFFunction(SNES snes, Vec x, Vec f, PetscCtx ctx)
    2259: {
    2260:   DM     dm;
    2261:   DMSNES sdm;

    2263:   PetscFunctionBegin;
    2264:   PetscCall(SNESGetDM(snes, &dm));
    2265:   PetscCall(DMGetDMSNES(dm, &sdm));
    2266:   /*  A(x)*x - b(x) */
    2267:   if (sdm->ops->computepfunction) {
    2268:     PetscCallBack("SNES Picard callback function", (*sdm->ops->computepfunction)(snes, x, f, sdm->pctx));
    2269:     PetscCall(VecScale(f, -1.0));
    2270:     /* Cannot share nonzero pattern because of the possible use of SNESComputeJacobianDefault() */
    2271:     if (!snes->picard) PetscCall(MatDuplicate(snes->jacobian_pre, MAT_DO_NOT_COPY_VALUES, &snes->picard));
    2272:     PetscCallBack("SNES Picard callback Jacobian", (*sdm->ops->computepjacobian)(snes, x, snes->picard, snes->picard, sdm->pctx));
    2273:     PetscCall(MatMultAdd(snes->picard, x, f, f));
    2274:   } else {
    2275:     PetscCallBack("SNES Picard callback Jacobian", (*sdm->ops->computepjacobian)(snes, x, snes->picard, snes->picard, sdm->pctx));
    2276:     PetscCall(MatMult(snes->picard, x, f));
    2277:   }
    2278:   PetscFunctionReturn(PETSC_SUCCESS);
    2279: }

    2281: /*@C
    2282:   SNESPicardComputeFunction - Compute the residual $A(x) x - b(x)$ using the callbacks registered by `SNESSetPicard()`

    2284:   Collective

    2286:   Input Parameters:
    2287: + snes - the `SNES` context
    2288: . x    - the current iterate
    2289: - ctx  - unused application context; the Picard callbacks are retrieved from the attached `DMSNES`

    2291:   Output Parameter:
    2292: . f - the residual vector

    2294:   Level: developer

    2296: .seealso: [](ch_snes), `SNES`, `SNESSetPicard()`, `SNESPicardComputeMFFunction()`, `SNESPicardComputeJacobian()`
    2297: @*/
    2298: PetscErrorCode SNESPicardComputeFunction(SNES snes, Vec x, Vec f, PetscCtx ctx)
    2299: {
    2300:   DM     dm;
    2301:   DMSNES sdm;

    2303:   PetscFunctionBegin;
    2304:   PetscCall(SNESGetDM(snes, &dm));
    2305:   PetscCall(DMGetDMSNES(dm, &sdm));
    2306:   /*  A(x)*x - b(x) */
    2307:   if (sdm->ops->computepfunction) {
    2308:     PetscCallBack("SNES Picard callback function", (*sdm->ops->computepfunction)(snes, x, f, sdm->pctx));
    2309:     PetscCall(VecScale(f, -1.0));
    2310:     PetscCallBack("SNES Picard callback Jacobian", (*sdm->ops->computepjacobian)(snes, x, snes->jacobian, snes->jacobian_pre, sdm->pctx));
    2311:     PetscCall(MatMultAdd(snes->jacobian_pre, x, f, f));
    2312:   } else {
    2313:     PetscCallBack("SNES Picard callback Jacobian", (*sdm->ops->computepjacobian)(snes, x, snes->jacobian, snes->jacobian_pre, sdm->pctx));
    2314:     PetscCall(MatMult(snes->jacobian_pre, x, f));
    2315:   }
    2316:   PetscFunctionReturn(PETSC_SUCCESS);
    2317: }

    2319: /*@C
    2320:   SNESPicardComputeJacobian - Trivial Jacobian assembly callback used by `SNESSetPicard()`; the Picard operator is filled in by `SNESPicardComputeFunction()`

    2322:   Collective

    2324:   Input Parameters:
    2325: + snes - the `SNES` context
    2326: . x1   - the current iterate (unused)
    2327: . J    - the Jacobian matrix to assemble
    2328: . B    - the preconditioning matrix (unused)
    2329: - ctx  - unused application context

    2331:   Level: developer

    2333:   Note:
    2334:   Only calls `MatAssemblyBegin()`/`MatAssemblyEnd()` on `J`, because the Picard iteration reuses the operator already assembled by `SNESPicardComputeFunction()`.

    2336: .seealso: [](ch_snes), `SNES`, `SNESSetPicard()`, `SNESPicardComputeFunction()`, `SNESPicardComputeMFFunction()`
    2337: @*/
    2338: PetscErrorCode SNESPicardComputeJacobian(SNES snes, Vec x1, Mat J, Mat B, PetscCtx ctx)
    2339: {
    2340:   PetscFunctionBegin;
    2341:   /* the jacobian matrix should be pre-filled in SNESPicardComputeFunction */
    2342:   /* must assembly if matrix-free to get the last SNES solution */
    2343:   PetscCall(MatAssemblyBegin(J, MAT_FINAL_ASSEMBLY));
    2344:   PetscCall(MatAssemblyEnd(J, MAT_FINAL_ASSEMBLY));
    2345:   PetscFunctionReturn(PETSC_SUCCESS);
    2346: }

    2348: /*@C
    2349:   SNESSetPicard - Use `SNES` to solve the system $A(x) x = bp(x) + b $ via a Picard type iteration (Picard linearization)

    2351:   Logically Collective

    2353:   Input Parameters:
    2354: + snes - the `SNES` context
    2355: . r    - vector to store function values, may be `NULL`
    2356: . bp   - function evaluation routine, may be `NULL`, for the calling sequence see `SNESFunctionFn`
    2357: . Amat - matrix with which $A(x) x - bp(x) - b$ is to be computed
    2358: . Pmat - matrix from which preconditioner is computed (usually the same as `Amat`)
    2359: . J    - function to compute matrix values, for the calling sequence see `SNESJacobianFn`
    2360: - ctx  - [optional] user-defined context for private data for the function evaluation routine (may be `NULL`)

    2362:   Level: intermediate

    2364:   Notes:
    2365:   It is often better to provide the nonlinear function $F()$ and some approximation to its Jacobian directly and use
    2366:   an approximate Newton solver. This interface is provided to allow porting/testing a previous Picard based code in PETSc before converting it to approximate Newton.

    2368:   One can call `SNESSetPicard()` or `SNESSetFunction()` (and possibly `SNESSetJacobian()`) but cannot call both

    2370:   Solves the equation $A(x) x = bp(x) - b$ via the defect correction algorithm $A(x^{n}) (x^{n+1} - x^{n}) = bp(x^{n}) + b - A(x^{n})x^{n}$.
    2371:   When an exact solver is used this corresponds to the "classic" Picard $A(x^{n}) x^{n+1} = bp(x^{n}) + b$ iteration.

    2373:   Run with `-snes_mf_operator` to solve the system with Newton's method using $A(x^{n})$ to construct the preconditioner.

    2375:   We implement the defect correction form of the Picard iteration because it converges much more generally when inexact linear solvers are used then
    2376:   the direct Picard iteration $A(x^n) x^{n+1} = bp(x^n) + b$

    2378:   There is some controversity over the definition of a Picard iteration for nonlinear systems but almost everyone agrees that it involves a linear solve and some
    2379:   believe it is the iteration  $A(x^{n}) x^{n+1} = b(x^{n})$ hence we use the name Picard. If anyone has an authoritative  reference that defines the Picard iteration
    2380:   different please contact us at petsc-dev@mcs.anl.gov and we'll have an entirely new argument \:-).

    2382:   When used with `-snes_mf_operator` this will run matrix-free Newton's method where the matrix-vector product is of the true Jacobian of $A(x)x - bp(x) - b$ and
    2383:   $A(x^{n})$ is used to build the preconditioner

    2385:   When used with `-snes_fd` this will compute the true Jacobian (very slowly one column at a time) and thus represent Newton's method.

    2387:   When used with `-snes_fd_coloring` this will compute the Jacobian via coloring and thus represent a faster implementation of Newton's method. But the
    2388:   the nonzero structure of the Jacobian is, in general larger than that of the Picard matrix $A$ so you must provide in $A$ the needed nonzero structure for the correct
    2389:   coloring. When using `DMDA` this may mean creating the matrix $A$ with `DMCreateMatrix()` using a wider stencil than strictly needed for $A$ or with a `DMDA_STENCIL_BOX`.
    2390:   See the comment in src/snes/tutorials/ex15.c.

    2392: .seealso: [](ch_snes), `SNES`, `SNESGetFunction()`, `SNESSetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESGetPicard()`, `SNESLineSearchPreCheckPicard()`,
    2393:           `SNESFunctionFn`, `SNESJacobianFn`
    2394: @*/
    2395: PetscErrorCode SNESSetPicard(SNES snes, Vec r, SNESFunctionFn *bp, Mat Amat, Mat Pmat, SNESJacobianFn *J, PetscCtx ctx)
    2396: {
    2397:   DM dm;

    2399:   PetscFunctionBegin;
    2401:   PetscCall(SNESGetDM(snes, &dm));
    2402:   PetscCall(DMSNESSetPicard(dm, bp, J, ctx));
    2403:   PetscCall(DMSNESSetMFFunction(dm, SNESPicardComputeMFFunction, ctx));
    2404:   PetscCall(SNESSetFunction(snes, r, SNESPicardComputeFunction, ctx));
    2405:   PetscCall(SNESSetJacobian(snes, Amat, Pmat, SNESPicardComputeJacobian, ctx));
    2406:   PetscFunctionReturn(PETSC_SUCCESS);
    2407: }

    2409: /*@C
    2410:   SNESGetPicard - Returns the context for the Picard iteration

    2412:   Not Collective, but `Vec` is parallel if `SNES` is parallel. Collective if `Vec` is requested, but has not been created yet.

    2414:   Input Parameter:
    2415: . snes - the `SNES` context

    2417:   Output Parameters:
    2418: + r    - the function (or `NULL`)
    2419: . f    - the function (or `NULL`);  for calling sequence see `SNESFunctionFn`
    2420: . Amat - the matrix used to defined the operation A(x) x - b(x) (or `NULL`)
    2421: . Pmat - the matrix from which the preconditioner will be constructed (or `NULL`)
    2422: . J    - the function for matrix evaluation (or `NULL`);  for calling sequence see `SNESJacobianFn`
    2423: - ctx  - the function context (or `NULL`)

    2425:   Level: advanced

    2427: .seealso: [](ch_snes), `SNESSetFunction()`, `SNESSetPicard()`, `SNESGetFunction()`, `SNESGetJacobian()`, `SNESGetDM()`, `SNESFunctionFn`, `SNESJacobianFn`
    2428: @*/
    2429: PetscErrorCode SNESGetPicard(SNES snes, Vec *r, SNESFunctionFn **f, Mat *Amat, Mat *Pmat, SNESJacobianFn **J, PetscCtxRt ctx)
    2430: {
    2431:   DM dm;

    2433:   PetscFunctionBegin;
    2435:   PetscCall(SNESGetFunction(snes, r, NULL, NULL));
    2436:   PetscCall(SNESGetJacobian(snes, Amat, Pmat, NULL, NULL));
    2437:   PetscCall(SNESGetDM(snes, &dm));
    2438:   PetscCall(DMSNESGetPicard(dm, f, J, ctx));
    2439:   PetscFunctionReturn(PETSC_SUCCESS);
    2440: }

    2442: /*@C
    2443:   SNESSetComputeInitialGuess - Sets a routine used to compute an initial guess for the nonlinear problem

    2445:   Logically Collective

    2447:   Input Parameters:
    2448: + snes - the `SNES` context
    2449: . func - function evaluation routine, see `SNESInitialGuessFn` for the calling sequence
    2450: - ctx  - [optional] user-defined context for private data for the
    2451:          function evaluation routine (may be `NULL`)

    2453:   Level: intermediate

    2455: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetFunction()`, `SNESGetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESInitialGuessFn`
    2456: @*/
    2457: PetscErrorCode SNESSetComputeInitialGuess(SNES snes, SNESInitialGuessFn *func, PetscCtx ctx)
    2458: {
    2459:   PetscFunctionBegin;
    2461:   if (func) snes->ops->computeinitialguess = func;
    2462:   if (ctx) snes->initialguessP = ctx;
    2463:   PetscFunctionReturn(PETSC_SUCCESS);
    2464: }

    2466: /*@C
    2467:   SNESGetRhs - Gets the vector for solving F(x) = `rhs`. If `rhs` is not set
    2468:   it assumes a zero right-hand side.

    2470:   Logically Collective

    2472:   Input Parameter:
    2473: . snes - the `SNES` context

    2475:   Output Parameter:
    2476: . rhs - the right-hand side vector or `NULL` if there is no right-hand side vector

    2478:   Level: intermediate

    2480: .seealso: [](ch_snes), `SNES`, `SNESGetSolution()`, `SNESGetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESSetFunction()`
    2481: @*/
    2482: PetscErrorCode SNESGetRhs(SNES snes, Vec *rhs)
    2483: {
    2484:   PetscFunctionBegin;
    2486:   PetscAssertPointer(rhs, 2);
    2487:   *rhs = snes->vec_rhs;
    2488:   PetscFunctionReturn(PETSC_SUCCESS);
    2489: }

    2491: /*@
    2492:   SNESComputeFunction - Calls the function that has been set with `SNESSetFunction()`.

    2494:   Collective

    2496:   Input Parameters:
    2497: + snes - the `SNES` context
    2498: - x    - input vector

    2500:   Output Parameter:
    2501: . f - function vector, as set by `SNESSetFunction()`

    2503:   Level: developer

    2505:   Notes:
    2506:   `SNESComputeFunction()` is typically used within nonlinear solvers
    2507:   implementations, so users would not generally call this routine themselves.

    2509:   When solving for $F(x) = b$, this routine computes $f = F(x) - b$.

    2511:   This function usually appears in the pattern.
    2512: .vb
    2513:   SNESComputeFunction(snes, x, f);
    2514:   VecNorm(f, &fnorm);
    2515:   SNESCheckFunctionDomainError(snes, fnorm); or SNESLineSearchCheckFunctionDomainError(ls, fnorm);
    2516: .ve
    2517:   to collectively handle the use of `SNESSetFunctionDomainError()` in the provided callback function.

    2519: .seealso: [](ch_snes), `SNES`, `SNESSetFunction()`, `SNESGetFunction()`, `SNESComputeMFFunction()`, `SNESSetFunctionDomainError()`
    2520: @*/
    2521: PetscErrorCode SNESComputeFunction(SNES snes, Vec x, Vec f)
    2522: {
    2523:   DM     dm;
    2524:   DMSNES sdm;

    2526:   PetscFunctionBegin;
    2530:   PetscCheckSameComm(snes, 1, x, 2);
    2531:   PetscCheckSameComm(snes, 1, f, 3);
    2532:   PetscCall(VecValidValues_Internal(x, 2, PETSC_TRUE));

    2534:   PetscCall(SNESGetDM(snes, &dm));
    2535:   PetscCall(DMGetDMSNES(dm, &sdm));
    2536:   PetscCheck(sdm->ops->computefunction || snes->vec_rhs, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "Must call SNESSetFunction() or SNESSetDM() before SNESComputeFunction(), likely called from SNESSolve().");
    2537:   if (sdm->ops->computefunction) {
    2538:     if (sdm->ops->computefunction != SNESObjectiveComputeFunctionDefaultFD) PetscCall(PetscLogEventBegin(SNES_FunctionEval, snes, x, f, 0));
    2539:     PetscCall(VecLockReadPush(x));
    2540:     /* ensure domainerror is false prior to computefunction evaluation (may not have been reset) */
    2541:     snes->functiondomainerror = PETSC_FALSE;
    2542:     {
    2543:       void           *ctx;
    2544:       SNESFunctionFn *computefunction;
    2545:       PetscCall(DMSNESGetFunction(dm, &computefunction, &ctx));
    2546:       PetscCallBack("SNES callback function", (*computefunction)(snes, x, f, ctx));
    2547:     }
    2548:     PetscCall(VecLockReadPop(x));
    2549:     if (sdm->ops->computefunction != SNESObjectiveComputeFunctionDefaultFD) PetscCall(PetscLogEventEnd(SNES_FunctionEval, snes, x, f, 0));
    2550:   } else /* if (snes->vec_rhs) */ {
    2551:     PetscCall(MatMult(snes->jacobian, x, f));
    2552:   }
    2553:   if (snes->vec_rhs) PetscCall(VecAXPY(f, -1.0, snes->vec_rhs));
    2554:   snes->nfuncs++;
    2555:   /*
    2556:      domainerror might not be set on all processes; so we tag vector locally with infinity and the next inner product or norm will
    2557:      propagate the value to all processes
    2558:   */
    2559:   PetscCall(VecFlag(f, snes->functiondomainerror));
    2560:   PetscFunctionReturn(PETSC_SUCCESS);
    2561: }

    2563: /*@
    2564:   SNESComputeMFFunction - Calls the function that has been set with `DMSNESSetMFFunction()`.

    2566:   Collective

    2568:   Input Parameters:
    2569: + snes - the `SNES` context
    2570: - x    - input vector

    2572:   Output Parameter:
    2573: . y - output vector

    2575:   Level: developer

    2577:   Notes:
    2578:   `SNESComputeMFFunction()` is used within the matrix-vector products called by the matrix created with `MatCreateSNESMF()`
    2579:   so users would not generally call this routine themselves.

    2581:   Since this function is intended for use with finite differencing it does not subtract the right-hand side vector provided with `SNESSolve()`
    2582:   while `SNESComputeFunction()` does. As such, this routine cannot be used with  `MatMFFDSetBase()` with a provided F function value even if it applies the
    2583:   same function as `SNESComputeFunction()` if a `SNESSolve()` right-hand side vector is use because the two functions difference would include this right hand side function.

    2585: .seealso: [](ch_snes), `SNES`, `SNESSetFunction()`, `SNESGetFunction()`, `SNESComputeFunction()`, `MatCreateSNESMF()`, `DMSNESSetMFFunction()`
    2586: @*/
    2587: PetscErrorCode SNESComputeMFFunction(SNES snes, Vec x, Vec y)
    2588: {
    2589:   DM     dm;
    2590:   DMSNES sdm;

    2592:   PetscFunctionBegin;
    2596:   PetscCheckSameComm(snes, 1, x, 2);
    2597:   PetscCheckSameComm(snes, 1, y, 3);
    2598:   PetscCall(VecValidValues_Internal(x, 2, PETSC_TRUE));

    2600:   PetscCall(SNESGetDM(snes, &dm));
    2601:   PetscCall(DMGetDMSNES(dm, &sdm));
    2602:   PetscCall(PetscLogEventBegin(SNES_FunctionEval, snes, x, y, 0));
    2603:   PetscCall(VecLockReadPush(x));
    2604:   /* ensure domainerror is false prior to computefunction evaluation (may not have been reset) */
    2605:   snes->functiondomainerror = PETSC_FALSE;
    2606:   PetscCallBack("SNES callback function", (*sdm->ops->computemffunction)(snes, x, y, sdm->mffunctionctx));
    2607:   PetscCall(VecLockReadPop(x));
    2608:   PetscCall(PetscLogEventEnd(SNES_FunctionEval, snes, x, y, 0));
    2609:   snes->nfuncs++;
    2610:   /*
    2611:      domainerror might not be set on all processes; so we tag vector locally with infinity and the next inner product or norm will
    2612:      propagate the value to all processes
    2613:   */
    2614:   PetscCall(VecFlag(y, snes->functiondomainerror));
    2615:   PetscFunctionReturn(PETSC_SUCCESS);
    2616: }

    2618: /*@
    2619:   SNESComputeNGS - Calls the Gauss-Seidel function that has been set with `SNESSetNGS()`.

    2621:   Collective

    2623:   Input Parameters:
    2624: + snes - the `SNES` context
    2625: . x    - input vector
    2626: - b    - rhs vector

    2628:   Output Parameter:
    2629: . x - new solution vector

    2631:   Level: developer

    2633:   Note:
    2634:   `SNESComputeNGS()` is typically used within composed nonlinear solver
    2635:   implementations, so most users would not generally call this routine
    2636:   themselves.

    2638: .seealso: [](ch_snes), `SNESNGSFn`, `SNESSetNGS()`, `SNESComputeFunction()`, `SNESNGS`
    2639: @*/
    2640: PetscErrorCode SNESComputeNGS(SNES snes, Vec b, Vec x)
    2641: {
    2642:   DM     dm;
    2643:   DMSNES sdm;

    2645:   PetscFunctionBegin;
    2649:   PetscCheckSameComm(snes, 1, x, 3);
    2650:   if (b) PetscCheckSameComm(snes, 1, b, 2);
    2651:   if (b) PetscCall(VecValidValues_Internal(b, 2, PETSC_TRUE));
    2652:   PetscCall(PetscLogEventBegin(SNES_NGSEval, snes, x, b, 0));
    2653:   PetscCall(SNESGetDM(snes, &dm));
    2654:   PetscCall(DMGetDMSNES(dm, &sdm));
    2655:   PetscCheck(sdm->ops->computegs, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "Must call SNESSetNGS() before SNESComputeNGS(), likely called from SNESSolve().");
    2656:   if (b) PetscCall(VecLockReadPush(b));
    2657:   PetscCallBack("SNES callback NGS", (*sdm->ops->computegs)(snes, x, b, sdm->gsctx));
    2658:   if (b) PetscCall(VecLockReadPop(b));
    2659:   PetscCall(PetscLogEventEnd(SNES_NGSEval, snes, x, b, 0));
    2660:   PetscFunctionReturn(PETSC_SUCCESS);
    2661: }

    2663: static PetscErrorCode SNESComputeFunction_FD(SNES snes, Vec Xin, Vec G)
    2664: {
    2665:   Vec          X;
    2666:   PetscScalar *g;
    2667:   PetscReal    f, f2;
    2668:   PetscInt     low, high, N, i;
    2669:   PetscBool    flg;
    2670:   PetscReal    h = .5 * PETSC_SQRT_MACHINE_EPSILON;

    2672:   PetscFunctionBegin;
    2673:   PetscCall(PetscOptionsGetReal(((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_fd_delta", &h, &flg));
    2674:   PetscCall(VecDuplicate(Xin, &X));
    2675:   PetscCall(VecCopy(Xin, X));
    2676:   PetscCall(VecGetSize(X, &N));
    2677:   PetscCall(VecGetOwnershipRange(X, &low, &high));
    2678:   PetscCall(VecSetOption(X, VEC_IGNORE_OFF_PROC_ENTRIES, PETSC_TRUE));
    2679:   PetscCall(VecGetArray(G, &g));
    2680:   for (i = 0; i < N; i++) {
    2681:     PetscCall(VecSetValue(X, i, -h, ADD_VALUES));
    2682:     PetscCall(VecAssemblyBegin(X));
    2683:     PetscCall(VecAssemblyEnd(X));
    2684:     PetscCall(SNESComputeObjective(snes, X, &f));
    2685:     PetscCall(VecSetValue(X, i, 2.0 * h, ADD_VALUES));
    2686:     PetscCall(VecAssemblyBegin(X));
    2687:     PetscCall(VecAssemblyEnd(X));
    2688:     PetscCall(SNESComputeObjective(snes, X, &f2));
    2689:     PetscCall(VecSetValue(X, i, -h, ADD_VALUES));
    2690:     PetscCall(VecAssemblyBegin(X));
    2691:     PetscCall(VecAssemblyEnd(X));
    2692:     if (i >= low && i < high) g[i - low] = (f2 - f) / (2.0 * h);
    2693:   }
    2694:   PetscCall(VecRestoreArray(G, &g));
    2695:   PetscCall(VecDestroy(&X));
    2696:   PetscFunctionReturn(PETSC_SUCCESS);
    2697: }

    2699: /*@
    2700:   SNESTestFunction - Computes the difference between the computed and finite-difference functions

    2702:   Collective

    2704:   Input Parameter:
    2705: . snes - the `SNES` context

    2707:   Options Database Keys:
    2708: + -snes_test_function      - compare the user provided function with one compute via finite differences to check for errors.
    2709: - -snes_test_function_view - display the user provided function, the finite difference function and the difference

    2711:   Level: developer

    2713: .seealso: [](ch_snes), `SNESTestJacobian()`, `SNESSetFunction()`, `SNESComputeFunction()`
    2714: @*/
    2715: PetscErrorCode SNESTestFunction(SNES snes)
    2716: {
    2717:   Vec               x, g1, g2, g3;
    2718:   PetscBool         complete_print = PETSC_FALSE;
    2719:   PetscReal         hcnorm, fdnorm, hcmax, fdmax, diffmax, diffnorm;
    2720:   PetscScalar       dot;
    2721:   MPI_Comm          comm;
    2722:   PetscViewer       viewer, mviewer;
    2723:   PetscViewerFormat format;
    2724:   PetscInt          tabs;
    2725:   static PetscBool  directionsprinted = PETSC_FALSE;
    2726:   SNESObjectiveFn  *objective;

    2728:   PetscFunctionBegin;
    2729:   PetscCall(SNESGetObjective(snes, &objective, NULL));
    2730:   if (!objective) PetscFunctionReturn(PETSC_SUCCESS);

    2732:   PetscObjectOptionsBegin((PetscObject)snes);
    2733:   PetscCall(PetscOptionsViewer("-snes_test_function_view", "View difference between hand-coded and finite difference function element entries", "None", &mviewer, &format, &complete_print));
    2734:   PetscOptionsEnd();

    2736:   PetscCall(PetscObjectGetComm((PetscObject)snes, &comm));
    2737:   PetscCall(PetscViewerASCIIGetStdout(comm, &viewer));
    2738:   PetscCall(PetscViewerASCIIGetTab(viewer, &tabs));
    2739:   PetscCall(PetscViewerASCIISetTab(viewer, ((PetscObject)snes)->tablevel));
    2740:   PetscCall(PetscViewerASCIIPrintf(viewer, "  ---------- Testing Function -------------\n"));
    2741:   if (!complete_print && !directionsprinted) {
    2742:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Run with -snes_test_function_view and optionally -snes_test_function <threshold> to show difference\n"));
    2743:     PetscCall(PetscViewerASCIIPrintf(viewer, "    of hand-coded and finite difference function entries greater than <threshold>.\n"));
    2744:   }
    2745:   if (!directionsprinted) {
    2746:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Testing hand-coded Function, if (for double precision runs) ||F - Ffd||/||F|| is\n"));
    2747:     PetscCall(PetscViewerASCIIPrintf(viewer, "    O(1.e-8), the hand-coded Function is probably correct.\n"));
    2748:     directionsprinted = PETSC_TRUE;
    2749:   }
    2750:   if (complete_print) PetscCall(PetscViewerPushFormat(mviewer, format));

    2752:   PetscCall(SNESGetSolution(snes, &x));
    2753:   PetscCall(VecDuplicate(x, &g1));
    2754:   PetscCall(VecDuplicate(x, &g2));
    2755:   PetscCall(VecDuplicate(x, &g3));
    2756:   PetscCall(SNESComputeFunction(snes, x, g1)); /* does not handle use of SNESSetFunctionDomainError() correctly */
    2757:   PetscCall(SNESComputeFunction_FD(snes, x, g2));

    2759:   PetscCall(VecNorm(g2, NORM_2, &fdnorm));
    2760:   PetscCall(VecNorm(g1, NORM_2, &hcnorm));
    2761:   PetscCall(VecNorm(g2, NORM_INFINITY, &fdmax));
    2762:   PetscCall(VecNorm(g1, NORM_INFINITY, &hcmax));
    2763:   PetscCall(VecDot(g1, g2, &dot));
    2764:   PetscCall(VecCopy(g1, g3));
    2765:   PetscCall(VecAXPY(g3, -1.0, g2));
    2766:   PetscCall(VecNorm(g3, NORM_2, &diffnorm));
    2767:   PetscCall(VecNorm(g3, NORM_INFINITY, &diffmax));
    2768:   PetscCall(PetscViewerASCIIPrintf(viewer, "  ||Ffd|| %g, ||F|| = %g, angle cosine = (Ffd'F)/||Ffd||||F|| = %g\n", (double)fdnorm, (double)hcnorm, (double)(PetscRealPart(dot) / (fdnorm * hcnorm))));
    2769:   PetscCall(PetscViewerASCIIPrintf(viewer, "  2-norm ||F - Ffd||/||F|| = %g, ||F - Ffd|| = %g\n", (double)(diffnorm / PetscMax(hcnorm, fdnorm)), (double)diffnorm));
    2770:   PetscCall(PetscViewerASCIIPrintf(viewer, "  max-norm ||F - Ffd||/||F|| = %g, ||F - Ffd|| = %g\n", (double)(diffmax / PetscMax(hcmax, fdmax)), (double)diffmax));

    2772:   if (complete_print) {
    2773:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Hand-coded function ----------\n"));
    2774:     PetscCall(VecView(g1, mviewer));
    2775:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Finite difference function ----------\n"));
    2776:     PetscCall(VecView(g2, mviewer));
    2777:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Hand-coded minus finite-difference function ----------\n"));
    2778:     PetscCall(VecView(g3, mviewer));
    2779:   }
    2780:   PetscCall(VecDestroy(&g1));
    2781:   PetscCall(VecDestroy(&g2));
    2782:   PetscCall(VecDestroy(&g3));

    2784:   if (complete_print) {
    2785:     PetscCall(PetscViewerPopFormat(mviewer));
    2786:     PetscCall(PetscViewerDestroy(&mviewer));
    2787:   }
    2788:   PetscCall(PetscViewerASCIISetTab(viewer, tabs));
    2789:   PetscFunctionReturn(PETSC_SUCCESS);
    2790: }

    2792: /*@
    2793:   SNESTestJacobian - Computes the difference between the computed and finite-difference Jacobians

    2795:   Collective

    2797:   Input Parameter:
    2798: . snes - the `SNES` context

    2800:   Output Parameters:
    2801: + Jnorm    - the Frobenius norm of the computed Jacobian, or `NULL`
    2802: - diffNorm - the Frobenius norm of the difference of the computed and finite-difference Jacobians, or `NULL`

    2804:   Options Database Keys:
    2805: + -snes_test_jacobian [threshold] - compare the user provided Jacobian with one compute via finite differences to check for errors.  If a threshold is given, display only those entries whose difference is greater than the threshold.
    2806: - -snes_test_jacobian_view        - display the user provided Jacobian, the finite difference Jacobian and the difference

    2808:   Level: developer

    2810:   Note:
    2811:   Directions and norms are printed to stdout if `diffNorm` is `NULL`.

    2813: .seealso: [](ch_snes), `SNESTestFunction()`, `SNESSetJacobian()`, `SNESComputeJacobian()`
    2814: @*/
    2815: PetscErrorCode SNESTestJacobian(SNES snes, PetscReal *Jnorm, PetscReal *diffNorm)
    2816: {
    2817:   Mat               A, B, C, D, jacobian;
    2818:   Vec               x = snes->vec_sol, f;
    2819:   PetscReal         nrm, gnorm;
    2820:   PetscReal         threshold = 1.e-5;
    2821:   void             *functx;
    2822:   PetscBool         complete_print = PETSC_FALSE, threshold_print = PETSC_FALSE, flg, istranspose;
    2823:   PetscBool         silent = diffNorm != PETSC_NULLPTR ? PETSC_TRUE : PETSC_FALSE;
    2824:   PetscViewer       viewer, mviewer;
    2825:   MPI_Comm          comm;
    2826:   PetscInt          tabs;
    2827:   static PetscBool  directionsprinted = PETSC_FALSE;
    2828:   PetscViewerFormat format;

    2830:   PetscFunctionBegin;
    2831:   PetscObjectOptionsBegin((PetscObject)snes);
    2832:   PetscCall(PetscOptionsReal("-snes_test_jacobian", "Threshold for element difference between hand-coded and finite difference being meaningful", "None", threshold, &threshold, NULL));
    2833:   PetscCall(PetscOptionsDeprecated("-snes_test_jacobian_display", "-snes_test_jacobian_view", "3.13", NULL));
    2834:   PetscCall(PetscOptionsViewer("-snes_test_jacobian_view", "View difference between hand-coded and finite difference Jacobians element entries", "None", &mviewer, &format, &complete_print));
    2835:   PetscCall(PetscOptionsDeprecated("-snes_test_jacobian_display_threshold", "-snes_test_jacobian", "3.13", "-snes_test_jacobian accepts an optional threshold (since v3.10)"));
    2836:   PetscCall(PetscOptionsReal("-snes_test_jacobian_display_threshold", "Display difference between hand-coded and finite difference Jacobians which exceed input threshold", "None", threshold, &threshold, &threshold_print));
    2837:   PetscOptionsEnd();

    2839:   PetscCall(PetscObjectGetComm((PetscObject)snes, &comm));
    2840:   PetscCall(PetscViewerASCIIGetStdout(comm, &viewer));
    2841:   PetscCall(PetscViewerASCIIGetTab(viewer, &tabs));
    2842:   PetscCall(PetscViewerASCIISetTab(viewer, ((PetscObject)snes)->tablevel));
    2843:   if (!silent) PetscCall(PetscViewerASCIIPrintf(viewer, "  ---------- Testing Jacobian -------------\n"));
    2844:   if (!complete_print && !silent && !directionsprinted) {
    2845:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Run with -snes_test_jacobian_view and optionally -snes_test_jacobian <threshold> to show difference\n"));
    2846:     PetscCall(PetscViewerASCIIPrintf(viewer, "    of hand-coded and finite difference Jacobian entries greater than <threshold>.\n"));
    2847:   }
    2848:   if (!directionsprinted && !silent) {
    2849:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Testing hand-coded Jacobian, if (for double precision runs) ||J - Jfd||_F/||J||_F is\n"));
    2850:     PetscCall(PetscViewerASCIIPrintf(viewer, "    O(1.e-8), the hand-coded Jacobian is probably correct.\n"));
    2851:     directionsprinted = PETSC_TRUE;
    2852:   }
    2853:   if (complete_print) PetscCall(PetscViewerPushFormat(mviewer, format));

    2855:   PetscCall(PetscObjectTypeCompare((PetscObject)snes->jacobian, MATMFFD, &flg));
    2856:   if (!flg) jacobian = snes->jacobian;
    2857:   else jacobian = snes->jacobian_pre;

    2859:   if (!x) PetscCall(MatCreateVecs(jacobian, &x, NULL));
    2860:   else PetscCall(PetscObjectReference((PetscObject)x));
    2861:   PetscCall(VecDuplicate(x, &f));

    2863:   /* evaluate the function at this point because SNESComputeJacobianDefault() assumes that the function has been evaluated and put into snes->vec_func */
    2864:   PetscCall(SNESComputeFunction(snes, x, f));
    2865:   PetscCall(VecDestroy(&f));
    2866:   PetscCall(PetscObjectTypeCompare((PetscObject)snes, SNESKSPTRANSPOSEONLY, &istranspose));
    2867:   while (jacobian) {
    2868:     Mat JT = NULL, Jsave = NULL;

    2870:     if (istranspose) {
    2871:       PetscCall(MatCreateTranspose(jacobian, &JT));
    2872:       Jsave    = jacobian;
    2873:       jacobian = JT;
    2874:     }
    2875:     PetscCall(PetscObjectBaseTypeCompareAny((PetscObject)jacobian, &flg, MATSEQAIJ, MATMPIAIJ, MATSEQDENSE, MATMPIDENSE, MATSEQBAIJ, MATMPIBAIJ, MATSEQSBAIJ, MATMPISBAIJ, ""));
    2876:     if (flg) {
    2877:       A = jacobian;
    2878:       PetscCall(PetscObjectReference((PetscObject)A));
    2879:     } else {
    2880:       PetscCall(MatComputeOperator(jacobian, MATAIJ, &A));
    2881:     }

    2883:     PetscCall(MatDuplicate(A, MAT_DO_NOT_COPY_VALUES, &B));
    2884:     PetscCall(MatSetOption(B, MAT_NEW_NONZERO_ALLOCATION_ERR, PETSC_FALSE));

    2886:     PetscCall(SNESGetFunction(snes, NULL, NULL, &functx));
    2887:     PetscCall(SNESComputeJacobianDefault(snes, x, B, B, functx));

    2889:     PetscCall(MatDuplicate(B, MAT_COPY_VALUES, &D));
    2890:     PetscCall(MatAYPX(D, -1.0, A, DIFFERENT_NONZERO_PATTERN));
    2891:     PetscCall(MatNorm(D, NORM_FROBENIUS, &nrm));
    2892:     PetscCall(MatNorm(A, NORM_FROBENIUS, &gnorm));
    2893:     PetscCall(MatDestroy(&D));
    2894:     if (!gnorm) gnorm = 1; /* just in case */
    2895:     if (!silent) PetscCall(PetscViewerASCIIPrintf(viewer, "  ||J - Jfd||_F/||J||_F = %g, ||J - Jfd||_F = %g\n", (double)(nrm / gnorm), (double)nrm));
    2896:     if (complete_print) {
    2897:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Hand-coded Jacobian ----------\n"));
    2898:       PetscCall(MatView(A, mviewer));
    2899:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Finite difference Jacobian ----------\n"));
    2900:       PetscCall(MatView(B, mviewer));
    2901:     }

    2903:     if (threshold_print || complete_print) {
    2904:       PetscInt           Istart, Iend, *ccols, bncols, cncols, j, row;
    2905:       PetscScalar       *cvals;
    2906:       const PetscInt    *bcols;
    2907:       const PetscScalar *bvals;

    2909:       PetscCall(MatDuplicate(A, MAT_DO_NOT_COPY_VALUES, &C));
    2910:       PetscCall(MatSetOption(C, MAT_NEW_NONZERO_ALLOCATION_ERR, PETSC_FALSE));

    2912:       PetscCall(MatAYPX(B, -1.0, A, DIFFERENT_NONZERO_PATTERN));
    2913:       PetscCall(MatGetOwnershipRange(B, &Istart, &Iend));

    2915:       for (row = Istart; row < Iend; row++) {
    2916:         PetscCall(MatGetRow(B, row, &bncols, &bcols, &bvals));
    2917:         PetscCall(PetscMalloc2(bncols, &ccols, bncols, &cvals));
    2918:         for (j = 0, cncols = 0; j < bncols; j++) {
    2919:           if (PetscAbsScalar(bvals[j]) > threshold) {
    2920:             ccols[cncols] = bcols[j];
    2921:             cvals[cncols] = bvals[j];
    2922:             cncols += 1;
    2923:           }
    2924:         }
    2925:         if (cncols) PetscCall(MatSetValues(C, 1, &row, cncols, ccols, cvals, INSERT_VALUES));
    2926:         PetscCall(MatRestoreRow(B, row, &bncols, &bcols, &bvals));
    2927:         PetscCall(PetscFree2(ccols, cvals));
    2928:       }
    2929:       PetscCall(MatAssemblyBegin(C, MAT_FINAL_ASSEMBLY));
    2930:       PetscCall(MatAssemblyEnd(C, MAT_FINAL_ASSEMBLY));
    2931:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Hand-coded minus finite-difference Jacobian with tolerance %g ----------\n", (double)threshold));
    2932:       PetscCall(MatView(C, complete_print ? mviewer : viewer));
    2933:       PetscCall(MatDestroy(&C));
    2934:     }
    2935:     PetscCall(MatDestroy(&A));
    2936:     PetscCall(MatDestroy(&B));
    2937:     PetscCall(MatDestroy(&JT));
    2938:     if (Jsave) jacobian = Jsave;
    2939:     if (jacobian != snes->jacobian_pre) {
    2940:       jacobian = snes->jacobian_pre;
    2941:       if (!silent) PetscCall(PetscViewerASCIIPrintf(viewer, "  ---------- Testing Jacobian for preconditioner -------------\n"));
    2942:     } else jacobian = NULL;
    2943:   }
    2944:   PetscCall(VecDestroy(&x));
    2945:   if (complete_print) PetscCall(PetscViewerPopFormat(mviewer));
    2946:   PetscCall(PetscViewerDestroy(&mviewer));
    2947:   PetscCall(PetscViewerASCIISetTab(viewer, tabs));

    2949:   if (Jnorm) *Jnorm = gnorm;
    2950:   if (diffNorm) *diffNorm = nrm;
    2951:   PetscFunctionReturn(PETSC_SUCCESS);
    2952: }

    2954: /*@
    2955:   SNESComputeJacobian - Computes the Jacobian matrix that has been set with `SNESSetJacobian()`.

    2957:   Collective

    2959:   Input Parameters:
    2960: + snes - the `SNES` context
    2961: - X    - input vector

    2963:   Output Parameters:
    2964: + A - Jacobian matrix
    2965: - B - optional matrix for building the preconditioner, usually the same as `A`

    2967:   Options Database Keys:
    2968: + -snes_lag_preconditioner lag          - how often to rebuild preconditioner
    2969: . -snes_lag_jacobian lag                - how often to rebuild Jacobian
    2970: . -snes_test_jacobian [threshold]       - compare the user provided Jacobian with one compute via finite differences to check for errors.
    2971:                                           If a threshold is given, display only those entries whose difference is greater than the threshold.
    2972: . -snes_test_jacobian_view [viewer]     - display the user provided Jacobian, the finite difference Jacobian and the difference between them to help users detect the location of errors in the user provided Jacobian
    2973: . -snes_compare_explicit                - Compare the computed Jacobian to the finite difference Jacobian and output the differences
    2974: . -snes_compare_explicit_draw           - Compare the computed Jacobian to the finite difference Jacobian and draw the result
    2975: . -snes_compare_explicit_contour        - Compare the computed Jacobian to the finite difference Jacobian and draw a contour plot with the result
    2976: . -snes_compare_operator                - Make the comparison options above use the operator instead of the matrix used to construct the preconditioner
    2977: . -snes_compare_coloring                - Compute the finite difference Jacobian using coloring and display norms of difference
    2978: . -snes_compare_coloring_display        - Compute the finite difference Jacobian using coloring and display verbose differences
    2979: . -snes_compare_coloring_threshold      - Display only those matrix entries that differ by more than a given threshold
    2980: . -snes_compare_coloring_threshold_atol - Absolute tolerance for difference in matrix entries to be displayed by `-snes_compare_coloring_threshold`
    2981: . -snes_compare_coloring_threshold_rtol - Relative tolerance for difference in matrix entries to be displayed by `-snes_compare_coloring_threshold`
    2982: . -snes_compare_coloring_draw           - Compute the finite difference Jacobian using coloring and draw differences
    2983: - -snes_compare_coloring_draw_contour   - Compute the finite difference Jacobian using coloring and show contours of matrices and differences

    2985:   Level: developer

    2987:   Note:
    2988:   Most users should not need to explicitly call this routine, as it
    2989:   is used internally within the nonlinear solvers.

    2991:   Developer Note:
    2992:   This has duplicative ways of checking the accuracy of the user provided Jacobian (see the options above). This is for historical reasons, the routine `SNESTestJacobian()` use to used
    2993:   with the `SNESType` of test that has been removed.

    2995: .seealso: [](ch_snes), `SNESSetJacobian()`, `KSPSetOperators()`, `MatStructure`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobian()`,
    2996:           `SNESSetJacobianDomainError()`, `SNESCheckJacobianDomainError()`, `SNESSetCheckJacobianDomainError()`
    2997: @*/
    2998: PetscErrorCode SNESComputeJacobian(SNES snes, Vec X, Mat A, Mat B)
    2999: {
    3000:   PetscBool flag;
    3001:   DM        dm;
    3002:   DMSNES    sdm;
    3003:   KSP       ksp;

    3005:   PetscFunctionBegin;
    3008:   PetscCheckSameComm(snes, 1, X, 2);
    3009:   PetscCall(VecValidValues_Internal(X, 2, PETSC_TRUE));
    3010:   PetscCall(SNESGetDM(snes, &dm));
    3011:   PetscCall(DMGetDMSNES(dm, &sdm));

    3013:   /* make sure that MatAssemblyBegin/End() is called on A matrix if it is matrix-free */
    3014:   if (snes->lagjacobian == -2) {
    3015:     snes->lagjacobian = -1;

    3017:     PetscCall(PetscInfo(snes, "Recomputing Jacobian/preconditioner because lag is -2 (means compute Jacobian, but then never again) \n"));
    3018:   } else if (snes->lagjacobian == -1) {
    3019:     PetscCall(PetscInfo(snes, "Reusing Jacobian/preconditioner because lag is -1\n"));
    3020:     PetscCall(PetscObjectTypeCompare((PetscObject)A, MATMFFD, &flag));
    3021:     if (flag) {
    3022:       PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
    3023:       PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
    3024:     }
    3025:     PetscFunctionReturn(PETSC_SUCCESS);
    3026:   } else if (snes->lagjacobian > 1 && (snes->iter + snes->jac_iter) % snes->lagjacobian) {
    3027:     PetscCall(PetscInfo(snes, "Reusing Jacobian/preconditioner because lag is %" PetscInt_FMT " and SNES iteration is %" PetscInt_FMT "\n", snes->lagjacobian, snes->iter));
    3028:     PetscCall(PetscObjectTypeCompare((PetscObject)A, MATMFFD, &flag));
    3029:     if (flag) {
    3030:       PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
    3031:       PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
    3032:     }
    3033:     PetscFunctionReturn(PETSC_SUCCESS);
    3034:   }
    3035:   if (snes->npc && snes->npcside == PC_LEFT) {
    3036:     PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
    3037:     PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
    3038:     PetscFunctionReturn(PETSC_SUCCESS);
    3039:   }

    3041:   PetscCall(PetscLogEventBegin(SNES_JacobianEval, snes, X, A, B));
    3042:   PetscCall(VecLockReadPush(X));
    3043:   {
    3044:     void           *ctx;
    3045:     SNESJacobianFn *J;
    3046:     PetscCall(DMSNESGetJacobian(dm, &J, &ctx));
    3047:     PetscCallBack("SNES callback Jacobian", (*J)(snes, X, A, B, ctx));
    3048:   }
    3049:   PetscCall(VecLockReadPop(X));
    3050:   PetscCall(PetscLogEventEnd(SNES_JacobianEval, snes, X, A, B));

    3052:   /* attach latest linearization point to the matrix used to construct the preconditioner */
    3053:   PetscCall(PetscObjectCompose((PetscObject)B, "__SNES_latest_X", (PetscObject)X));

    3055:   /* the next line ensures that snes->ksp exists */
    3056:   PetscCall(SNESGetKSP(snes, &ksp));
    3057:   if (snes->lagpreconditioner == -2) {
    3058:     PetscCall(PetscInfo(snes, "Rebuilding preconditioner exactly once since lag is -2\n"));
    3059:     PetscCall(KSPSetReusePreconditioner(snes->ksp, PETSC_FALSE));
    3060:     snes->lagpreconditioner = -1;
    3061:   } else if (snes->lagpreconditioner == -1) {
    3062:     PetscCall(PetscInfo(snes, "Reusing preconditioner because lag is -1\n"));
    3063:     PetscCall(KSPSetReusePreconditioner(snes->ksp, PETSC_TRUE));
    3064:   } else if (snes->lagpreconditioner > 1 && (snes->iter + snes->pre_iter) % snes->lagpreconditioner) {
    3065:     PetscCall(PetscInfo(snes, "Reusing preconditioner because lag is %" PetscInt_FMT " and SNES iteration is %" PetscInt_FMT "\n", snes->lagpreconditioner, snes->iter));
    3066:     PetscCall(KSPSetReusePreconditioner(snes->ksp, PETSC_TRUE));
    3067:   } else {
    3068:     PetscCall(PetscInfo(snes, "Rebuilding preconditioner\n"));
    3069:     PetscCall(KSPSetReusePreconditioner(snes->ksp, PETSC_FALSE));
    3070:   }

    3072:   /* monkey business to allow testing Jacobians in multilevel solvers.
    3073:      This is needed because the SNESTestXXX interface does not accept vectors and matrices */
    3074:   {
    3075:     Vec xsave            = snes->vec_sol;
    3076:     Mat jacobiansave     = snes->jacobian;
    3077:     Mat jacobian_presave = snes->jacobian_pre;

    3079:     snes->vec_sol      = X;
    3080:     snes->jacobian     = A;
    3081:     snes->jacobian_pre = B;
    3082:     if (snes->testFunc) PetscCall(SNESTestFunction(snes));
    3083:     if (snes->testJac) PetscCall(SNESTestJacobian(snes, NULL, NULL));

    3085:     snes->vec_sol      = xsave;
    3086:     snes->jacobian     = jacobiansave;
    3087:     snes->jacobian_pre = jacobian_presave;
    3088:   }

    3090:   {
    3091:     PetscBool flag = PETSC_FALSE, flag_draw = PETSC_FALSE, flag_contour = PETSC_FALSE, flag_operator = PETSC_FALSE;
    3092:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_explicit", NULL, NULL, &flag));
    3093:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_explicit_draw", NULL, NULL, &flag_draw));
    3094:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_explicit_draw_contour", NULL, NULL, &flag_contour));
    3095:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_operator", NULL, NULL, &flag_operator));
    3096:     if (flag || flag_draw || flag_contour) {
    3097:       Mat         Bexp_mine = NULL, Bexp, FDexp;
    3098:       PetscViewer vdraw, vstdout;
    3099:       PetscBool   flg;
    3100:       if (flag_operator) {
    3101:         PetscCall(MatComputeOperator(A, MATAIJ, &Bexp_mine));
    3102:         Bexp = Bexp_mine;
    3103:       } else {
    3104:         /* See if the matrix used to construct the preconditioner can be viewed and added directly */
    3105:         PetscCall(PetscObjectBaseTypeCompareAny((PetscObject)B, &flg, MATSEQAIJ, MATMPIAIJ, MATSEQDENSE, MATMPIDENSE, MATSEQBAIJ, MATMPIBAIJ, MATSEQSBAIJ, MATMPISBAIJ, ""));
    3106:         if (flg) Bexp = B;
    3107:         else {
    3108:           /* If the "preconditioning" matrix is itself MATSHELL or some other type without direct support */
    3109:           PetscCall(MatComputeOperator(B, MATAIJ, &Bexp_mine));
    3110:           Bexp = Bexp_mine;
    3111:         }
    3112:       }
    3113:       PetscCall(MatConvert(Bexp, MATSAME, MAT_INITIAL_MATRIX, &FDexp));
    3114:       PetscCall(SNESComputeJacobianDefault(snes, X, FDexp, FDexp, NULL));
    3115:       PetscCall(PetscViewerASCIIGetStdout(PetscObjectComm((PetscObject)snes), &vstdout));
    3116:       if (flag_draw || flag_contour) {
    3117:         PetscCall(PetscViewerDrawOpen(PetscObjectComm((PetscObject)snes), NULL, "Explicit Jacobians", PETSC_DECIDE, PETSC_DECIDE, 300, 300, &vdraw));
    3118:         if (flag_contour) PetscCall(PetscViewerPushFormat(vdraw, PETSC_VIEWER_DRAW_CONTOUR));
    3119:       } else vdraw = NULL;
    3120:       PetscCall(PetscViewerASCIIPrintf(vstdout, "Explicit %s\n", flag_operator ? "Jacobian" : "preconditioning Jacobian"));
    3121:       if (flag) PetscCall(MatView(Bexp, vstdout));
    3122:       if (vdraw) PetscCall(MatView(Bexp, vdraw));
    3123:       PetscCall(PetscViewerASCIIPrintf(vstdout, "Finite difference Jacobian\n"));
    3124:       if (flag) PetscCall(MatView(FDexp, vstdout));
    3125:       if (vdraw) PetscCall(MatView(FDexp, vdraw));
    3126:       PetscCall(MatAYPX(FDexp, -1.0, Bexp, SAME_NONZERO_PATTERN));
    3127:       PetscCall(PetscViewerASCIIPrintf(vstdout, "User-provided matrix minus finite difference Jacobian\n"));
    3128:       if (flag) PetscCall(MatView(FDexp, vstdout));
    3129:       if (vdraw) { /* Always use contour for the difference */
    3130:         PetscCall(PetscViewerPushFormat(vdraw, PETSC_VIEWER_DRAW_CONTOUR));
    3131:         PetscCall(MatView(FDexp, vdraw));
    3132:         PetscCall(PetscViewerPopFormat(vdraw));
    3133:       }
    3134:       if (flag_contour) PetscCall(PetscViewerPopFormat(vdraw));
    3135:       PetscCall(PetscViewerDestroy(&vdraw));
    3136:       PetscCall(MatDestroy(&Bexp_mine));
    3137:       PetscCall(MatDestroy(&FDexp));
    3138:     }
    3139:   }
    3140:   {
    3141:     PetscBool flag = PETSC_FALSE, flag_display = PETSC_FALSE, flag_draw = PETSC_FALSE, flag_contour = PETSC_FALSE, flag_threshold = PETSC_FALSE;
    3142:     PetscReal threshold_atol = PETSC_SQRT_MACHINE_EPSILON, threshold_rtol = 10 * PETSC_SQRT_MACHINE_EPSILON;
    3143:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring", NULL, NULL, &flag));
    3144:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_display", NULL, NULL, &flag_display));
    3145:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_draw", NULL, NULL, &flag_draw));
    3146:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_draw_contour", NULL, NULL, &flag_contour));
    3147:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_threshold", NULL, NULL, &flag_threshold));
    3148:     if (flag_threshold) {
    3149:       PetscCall(PetscOptionsGetReal(((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_threshold_rtol", &threshold_rtol, NULL));
    3150:       PetscCall(PetscOptionsGetReal(((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_threshold_atol", &threshold_atol, NULL));
    3151:     }
    3152:     if (flag || flag_display || flag_draw || flag_contour || flag_threshold) {
    3153:       Mat             Bfd;
    3154:       PetscViewer     vdraw, vstdout;
    3155:       MatColoring     coloring;
    3156:       ISColoring      iscoloring;
    3157:       MatFDColoring   matfdcoloring;
    3158:       SNESFunctionFn *func;
    3159:       void           *funcctx;
    3160:       PetscReal       norm1, norm2, normmax;

    3162:       PetscCall(MatDuplicate(B, MAT_DO_NOT_COPY_VALUES, &Bfd));
    3163:       PetscCall(MatColoringCreate(Bfd, &coloring));
    3164:       PetscCall(MatColoringSetType(coloring, MATCOLORINGSL));
    3165:       PetscCall(MatColoringSetFromOptions(coloring));
    3166:       PetscCall(MatColoringApply(coloring, &iscoloring));
    3167:       PetscCall(MatColoringDestroy(&coloring));
    3168:       PetscCall(MatFDColoringCreate(Bfd, iscoloring, &matfdcoloring));
    3169:       PetscCall(MatFDColoringSetFromOptions(matfdcoloring));
    3170:       PetscCall(MatFDColoringSetUp(Bfd, iscoloring, matfdcoloring));
    3171:       PetscCall(ISColoringDestroy(&iscoloring));

    3173:       /* This method of getting the function is currently unreliable since it doesn't work for DM local functions. */
    3174:       PetscCall(SNESGetFunction(snes, NULL, &func, &funcctx));
    3175:       PetscCall(MatFDColoringSetFunction(matfdcoloring, (MatFDColoringFn *)func, funcctx));
    3176:       PetscCall(PetscObjectSetOptionsPrefix((PetscObject)matfdcoloring, ((PetscObject)snes)->prefix));
    3177:       PetscCall(PetscObjectAppendOptionsPrefix((PetscObject)matfdcoloring, "coloring_"));
    3178:       PetscCall(MatFDColoringSetFromOptions(matfdcoloring));
    3179:       PetscCall(MatFDColoringApply(Bfd, matfdcoloring, X, snes));
    3180:       PetscCall(MatFDColoringDestroy(&matfdcoloring));

    3182:       PetscCall(PetscViewerASCIIGetStdout(PetscObjectComm((PetscObject)snes), &vstdout));
    3183:       if (flag_draw || flag_contour) {
    3184:         PetscCall(PetscViewerDrawOpen(PetscObjectComm((PetscObject)snes), NULL, "Colored Jacobians", PETSC_DECIDE, PETSC_DECIDE, 300, 300, &vdraw));
    3185:         if (flag_contour) PetscCall(PetscViewerPushFormat(vdraw, PETSC_VIEWER_DRAW_CONTOUR));
    3186:       } else vdraw = NULL;
    3187:       PetscCall(PetscViewerASCIIPrintf(vstdout, "Explicit preconditioning Jacobian\n"));
    3188:       if (flag_display) PetscCall(MatView(B, vstdout));
    3189:       if (vdraw) PetscCall(MatView(B, vdraw));
    3190:       PetscCall(PetscViewerASCIIPrintf(vstdout, "Colored Finite difference Jacobian\n"));
    3191:       if (flag_display) PetscCall(MatView(Bfd, vstdout));
    3192:       if (vdraw) PetscCall(MatView(Bfd, vdraw));
    3193:       PetscCall(MatAYPX(Bfd, -1.0, B, SAME_NONZERO_PATTERN));
    3194:       PetscCall(MatNorm(Bfd, NORM_1, &norm1));
    3195:       PetscCall(MatNorm(Bfd, NORM_FROBENIUS, &norm2));
    3196:       PetscCall(MatNorm(Bfd, NORM_MAX, &normmax));
    3197:       PetscCall(PetscViewerASCIIPrintf(vstdout, "User-provided matrix minus finite difference Jacobian, norm1=%g normFrob=%g normmax=%g\n", (double)norm1, (double)norm2, (double)normmax));
    3198:       if (flag_display) PetscCall(MatView(Bfd, vstdout));
    3199:       if (vdraw) { /* Always use contour for the difference */
    3200:         PetscCall(PetscViewerPushFormat(vdraw, PETSC_VIEWER_DRAW_CONTOUR));
    3201:         PetscCall(MatView(Bfd, vdraw));
    3202:         PetscCall(PetscViewerPopFormat(vdraw));
    3203:       }
    3204:       if (flag_contour) PetscCall(PetscViewerPopFormat(vdraw));

    3206:       if (flag_threshold) {
    3207:         PetscInt bs, rstart, rend, i;
    3208:         PetscCall(MatGetBlockSize(B, &bs));
    3209:         PetscCall(MatGetOwnershipRange(B, &rstart, &rend));
    3210:         for (i = rstart; i < rend; i++) {
    3211:           const PetscScalar *ba, *ca;
    3212:           const PetscInt    *bj, *cj;
    3213:           PetscInt           bn, cn, j, maxentrycol = -1, maxdiffcol = -1, maxrdiffcol = -1;
    3214:           PetscReal          maxentry = 0, maxdiff = 0, maxrdiff = 0;
    3215:           PetscCall(MatGetRow(B, i, &bn, &bj, &ba));
    3216:           PetscCall(MatGetRow(Bfd, i, &cn, &cj, &ca));
    3217:           PetscCheck(bn == cn, ((PetscObject)A)->comm, PETSC_ERR_PLIB, "Unexpected different nonzero pattern in -snes_compare_coloring_threshold");
    3218:           for (j = 0; j < bn; j++) {
    3219:             PetscReal rdiff = PetscAbsScalar(ca[j]) / (threshold_atol + threshold_rtol * PetscAbsScalar(ba[j]));
    3220:             if (PetscAbsScalar(ba[j]) > PetscAbs(maxentry)) {
    3221:               maxentrycol = bj[j];
    3222:               maxentry    = PetscRealPart(ba[j]);
    3223:             }
    3224:             if (PetscAbsScalar(ca[j]) > PetscAbs(maxdiff)) {
    3225:               maxdiffcol = bj[j];
    3226:               maxdiff    = PetscRealPart(ca[j]);
    3227:             }
    3228:             if (rdiff > maxrdiff) {
    3229:               maxrdiffcol = bj[j];
    3230:               maxrdiff    = rdiff;
    3231:             }
    3232:           }
    3233:           if (maxrdiff > 1) {
    3234:             PetscCall(PetscViewerASCIIPrintf(vstdout, "row %" PetscInt_FMT " (maxentry=%g at %" PetscInt_FMT ", maxdiff=%g at %" PetscInt_FMT ", maxrdiff=%g at %" PetscInt_FMT "):", i, (double)maxentry, maxentrycol, (double)maxdiff, maxdiffcol, (double)maxrdiff, maxrdiffcol));
    3235:             for (j = 0; j < bn; j++) {
    3236:               PetscReal rdiff;
    3237:               rdiff = PetscAbsScalar(ca[j]) / (threshold_atol + threshold_rtol * PetscAbsScalar(ba[j]));
    3238:               if (rdiff > 1) PetscCall(PetscViewerASCIIPrintf(vstdout, " (%" PetscInt_FMT ",%g:%g)", bj[j], (double)PetscRealPart(ba[j]), (double)PetscRealPart(ca[j])));
    3239:             }
    3240:             PetscCall(PetscViewerASCIIPrintf(vstdout, "\n"));
    3241:           }
    3242:           PetscCall(MatRestoreRow(B, i, &bn, &bj, &ba));
    3243:           PetscCall(MatRestoreRow(Bfd, i, &cn, &cj, &ca));
    3244:         }
    3245:       }
    3246:       PetscCall(PetscViewerDestroy(&vdraw));
    3247:       PetscCall(MatDestroy(&Bfd));
    3248:     }
    3249:   }
    3250:   PetscFunctionReturn(PETSC_SUCCESS);
    3251: }

    3253: /*@C
    3254:   SNESSetJacobian - Sets the function to compute Jacobian as well as the
    3255:   location to store the matrix.

    3257:   Logically Collective

    3259:   Input Parameters:
    3260: + snes - the `SNES` context
    3261: . Amat - the matrix that defines the (approximate) Jacobian
    3262: . Pmat - the matrix to be used in constructing the preconditioner, usually the same as `Amat`.
    3263: . J    - Jacobian evaluation routine (if `NULL` then `SNES` retains any previously set value), see `SNESJacobianFn` for details
    3264: - ctx  - [optional] user-defined context for private data for the
    3265:          Jacobian evaluation routine (may be `NULL`) (if `NULL` then `SNES` retains any previously set value)

    3267:   Level: beginner

    3269:   Notes:
    3270:   If the `Amat` matrix and `Pmat` matrix are different you must call `MatAssemblyBegin()`/`MatAssemblyEnd()` on
    3271:   each matrix.

    3273:   If you know the operator `Amat` has a null space you can use `MatSetNullSpace()` and `MatSetTransposeNullSpace()` to supply the null
    3274:   space to `Amat` and the `KSP` solvers will automatically use that null space as needed during the solution process.

    3276:   If using `SNESComputeJacobianDefaultColor()` to assemble a Jacobian, the `ctx` argument
    3277:   must be a `MatFDColoring`.

    3279:   Other defect-correction schemes can be used by computing a different matrix in place of the Jacobian.  One common
    3280:   example is to use the "Picard linearization" which only differentiates through the highest order parts of each term using `SNESSetPicard()`

    3282: .seealso: [](ch_snes), `SNES`, `KSPSetOperators()`, `SNESSetFunction()`, `MatMFFDComputeJacobian()`, `SNESComputeJacobianDefaultColor()`, `MatStructure`,
    3283:           `SNESSetPicard()`, `SNESJacobianFn`, `SNESFunctionFn`
    3284: @*/
    3285: PetscErrorCode SNESSetJacobian(SNES snes, Mat Amat, Mat Pmat, SNESJacobianFn *J, PetscCtx ctx)
    3286: {
    3287:   DM dm;

    3289:   PetscFunctionBegin;
    3293:   if (Amat) PetscCheckSameComm(snes, 1, Amat, 2);
    3294:   if (Pmat) PetscCheckSameComm(snes, 1, Pmat, 3);
    3295:   PetscCall(SNESGetDM(snes, &dm));
    3296:   PetscCall(DMSNESSetJacobian(dm, J, ctx));
    3297:   if (Amat) {
    3298:     PetscCall(PetscObjectReference((PetscObject)Amat));
    3299:     PetscCall(MatDestroy(&snes->jacobian));

    3301:     snes->jacobian = Amat;
    3302:   }
    3303:   if (Pmat) {
    3304:     PetscCall(PetscObjectReference((PetscObject)Pmat));
    3305:     PetscCall(MatDestroy(&snes->jacobian_pre));

    3307:     snes->jacobian_pre = Pmat;
    3308:   }
    3309:   PetscFunctionReturn(PETSC_SUCCESS);
    3310: }

    3312: /*@C
    3313:   SNESGetJacobian - Returns the Jacobian matrix and optionally the user
    3314:   provided context for evaluating the Jacobian.

    3316:   Not Collective, but `Mat` object will be parallel if `SNES` is

    3318:   Input Parameter:
    3319: . snes - the nonlinear solver context

    3321:   Output Parameters:
    3322: + Amat - location to stash (approximate) Jacobian matrix (or `NULL`)
    3323: . Pmat - location to stash matrix used to compute the preconditioner (or `NULL`)
    3324: . J    - location to put Jacobian function (or `NULL`), for calling sequence see `SNESJacobianFn`
    3325: - ctx  - location to stash Jacobian ctx (or `NULL`)

    3327:   Level: advanced

    3329: .seealso: [](ch_snes), `SNES`, `Mat`, `SNESSetJacobian()`, `SNESComputeJacobian()`, `SNESJacobianFn`, `SNESGetFunction()`
    3330: @*/
    3331: PetscErrorCode SNESGetJacobian(SNES snes, Mat *Amat, Mat *Pmat, SNESJacobianFn **J, PetscCtxRt ctx)
    3332: {
    3333:   DM dm;

    3335:   PetscFunctionBegin;
    3337:   if (Amat) *Amat = snes->jacobian;
    3338:   if (Pmat) *Pmat = snes->jacobian_pre;
    3339:   PetscCall(SNESGetDM(snes, &dm));
    3340:   PetscCall(DMSNESGetJacobian(dm, J, ctx));
    3341:   PetscFunctionReturn(PETSC_SUCCESS);
    3342: }

    3344: static PetscErrorCode SNESSetDefaultComputeJacobian(SNES snes)
    3345: {
    3346:   DM     dm;
    3347:   DMSNES sdm;

    3349:   PetscFunctionBegin;
    3350:   PetscCall(SNESGetDM(snes, &dm));
    3351:   PetscCall(DMGetDMSNES(dm, &sdm));
    3352:   if (!sdm->ops->computejacobian && snes->jacobian_pre) {
    3353:     DM        dm;
    3354:     PetscBool isdense, ismf;

    3356:     PetscCall(SNESGetDM(snes, &dm));
    3357:     PetscCall(PetscObjectTypeCompareAny((PetscObject)snes->jacobian_pre, &isdense, MATSEQDENSE, MATMPIDENSE, MATDENSE, NULL));
    3358:     PetscCall(PetscObjectTypeCompareAny((PetscObject)snes->jacobian_pre, &ismf, MATMFFD, MATSHELL, NULL));
    3359:     if (isdense) PetscCall(DMSNESSetJacobian(dm, SNESComputeJacobianDefault, NULL));
    3360:     else if (!ismf) PetscCall(DMSNESSetJacobian(dm, SNESComputeJacobianDefaultColor, NULL));
    3361:   }
    3362:   PetscFunctionReturn(PETSC_SUCCESS);
    3363: }

    3365: /*@
    3366:   SNESSetUp - Sets up the internal data structures for the later use
    3367:   of a nonlinear solver `SNESSolve()`.

    3369:   Collective

    3371:   Input Parameter:
    3372: . snes - the `SNES` context

    3374:   Level: advanced

    3376:   Note:
    3377:   For basic use of the `SNES` solvers the user does not need to explicitly call
    3378:   `SNESSetUp()`, since these actions will automatically occur during
    3379:   the call to `SNESSolve()`.  However, if one wishes to control this
    3380:   phase separately, `SNESSetUp()` should be called after `SNESCreate()`
    3381:   and optional routines of the form SNESSetXXX(), but before `SNESSolve()`.

    3383: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESSolve()`, `SNESDestroy()`, `SNESSetFromOptions()`
    3384: @*/
    3385: PetscErrorCode SNESSetUp(SNES snes)
    3386: {
    3387:   DM             dm;
    3388:   DMSNES         sdm;
    3389:   SNESLineSearch linesearch, pclinesearch;
    3390:   void          *lsprectx, *lspostctx;
    3391:   PetscBool      mf_operator, mf;
    3392:   Vec            f, fpc;
    3393:   void          *funcctx;
    3394:   void          *jacctx, *appctx;
    3395:   Mat            j, jpre;
    3396:   PetscErrorCode (*precheck)(SNESLineSearch, Vec, Vec, PetscBool *, PetscCtx);
    3397:   PetscErrorCode (*postcheck)(SNESLineSearch, Vec, Vec, Vec, PetscBool *, PetscBool *, PetscCtx);
    3398:   SNESFunctionFn *func;
    3399:   SNESJacobianFn *jac;

    3401:   PetscFunctionBegin;
    3403:   if (snes->setupcalled) PetscFunctionReturn(PETSC_SUCCESS);
    3404:   PetscCall(PetscLogEventBegin(SNES_SetUp, snes, 0, 0, 0));

    3406:   if (!((PetscObject)snes)->type_name) PetscCall(SNESSetType(snes, SNESNEWTONLS));

    3408:   PetscCall(SNESGetFunction(snes, &snes->vec_func, NULL, NULL));

    3410:   PetscCall(SNESGetDM(snes, &dm));
    3411:   PetscCall(DMGetDMSNES(dm, &sdm));
    3412:   PetscCall(SNESSetDefaultComputeJacobian(snes));

    3414:   if (!snes->vec_func) PetscCall(DMCreateGlobalVector(dm, &snes->vec_func));

    3416:   if (!snes->ksp) PetscCall(SNESGetKSP(snes, &snes->ksp));

    3418:   if (snes->linesearch) {
    3419:     PetscCall(SNESGetLineSearch(snes, &snes->linesearch));
    3420:     PetscCall(SNESLineSearchSetFunction(snes->linesearch, SNESComputeFunction));
    3421:   }

    3423:   PetscCall(SNESGetUseMatrixFree(snes, &mf_operator, &mf));
    3424:   if (snes->npc && snes->npcside == PC_LEFT) {
    3425:     snes->mf          = PETSC_TRUE;
    3426:     snes->mf_operator = PETSC_FALSE;
    3427:   }

    3429:   if (snes->npc) {
    3430:     /* copy the DM over */
    3431:     PetscCall(SNESGetDM(snes, &dm));
    3432:     PetscCall(SNESSetDM(snes->npc, dm));

    3434:     PetscCall(SNESGetFunction(snes, &f, &func, &funcctx));
    3435:     PetscCall(VecDuplicate(f, &fpc));
    3436:     PetscCall(SNESSetFunction(snes->npc, fpc, func, funcctx));
    3437:     PetscCall(SNESGetJacobian(snes, &j, &jpre, &jac, &jacctx));
    3438:     PetscCall(SNESSetJacobian(snes->npc, j, jpre, jac, jacctx));
    3439:     PetscCall(SNESGetApplicationContext(snes, &appctx));
    3440:     PetscCall(SNESSetApplicationContext(snes->npc, appctx));
    3441:     PetscCall(SNESSetUseMatrixFree(snes->npc, mf_operator, mf));
    3442:     PetscCall(VecDestroy(&fpc));

    3444:     /* copy the function pointers over */
    3445:     PetscCall(PetscObjectCopyFortranFunctionPointers((PetscObject)snes, (PetscObject)snes->npc));

    3447:     /* default to 1 iteration */
    3448:     PetscCall(SNESSetTolerances(snes->npc, 0.0, 0.0, 0.0, 1, snes->npc->max_funcs));
    3449:     if (snes->npcside == PC_RIGHT) {
    3450:       PetscCall(SNESSetNormSchedule(snes->npc, SNES_NORM_FINAL_ONLY));
    3451:     } else {
    3452:       PetscCall(SNESSetNormSchedule(snes->npc, SNES_NORM_NONE));
    3453:     }
    3454:     PetscCall(SNESSetFromOptions(snes->npc));

    3456:     /* copy the line search context over */
    3457:     if (snes->linesearch && snes->npc->linesearch) {
    3458:       PetscCall(SNESGetLineSearch(snes, &linesearch));
    3459:       PetscCall(SNESGetLineSearch(snes->npc, &pclinesearch));
    3460:       PetscCall(SNESLineSearchGetPreCheck(linesearch, &precheck, &lsprectx));
    3461:       PetscCall(SNESLineSearchGetPostCheck(linesearch, &postcheck, &lspostctx));
    3462:       PetscCall(SNESLineSearchSetPreCheck(pclinesearch, precheck, lsprectx));
    3463:       PetscCall(SNESLineSearchSetPostCheck(pclinesearch, postcheck, lspostctx));
    3464:       PetscCall(PetscObjectCopyFortranFunctionPointers((PetscObject)linesearch, (PetscObject)pclinesearch));
    3465:     }
    3466:   }
    3467:   if (snes->mf) PetscCall(SNESSetUpMatrixFree_Private(snes, snes->mf_operator, snes->mf_version));
    3468:   if (snes->ops->ctxcompute && !snes->ctx) PetscCallBack("SNES callback compute application context", (*snes->ops->ctxcompute)(snes, &snes->ctx));

    3470:   snes->jac_iter = 0;
    3471:   snes->pre_iter = 0;

    3473:   PetscTryTypeMethod(snes, setup);

    3475:   PetscCall(SNESSetDefaultComputeJacobian(snes));

    3477:   if (snes->npc && snes->npcside == PC_LEFT) {
    3478:     if (snes->functype == SNES_FUNCTION_PRECONDITIONED) {
    3479:       if (snes->linesearch) {
    3480:         PetscCall(SNESGetLineSearch(snes, &linesearch));
    3481:         PetscCall(SNESLineSearchSetFunction(linesearch, SNESComputeFunctionDefaultNPC));
    3482:       }
    3483:     }
    3484:   }
    3485:   PetscCall(PetscLogEventEnd(SNES_SetUp, snes, 0, 0, 0));
    3486:   snes->setupcalled = PETSC_TRUE;
    3487:   PetscFunctionReturn(PETSC_SUCCESS);
    3488: }

    3490: /*@
    3491:   SNESReset - Resets a `SNES` context to the state it was in before `SNESSetUp()` was called and removes any allocated `Vec` and `Mat` from its data structures

    3493:   Collective

    3495:   Input Parameter:
    3496: . snes - the nonlinear iterative solver context obtained from `SNESCreate()`

    3498:   Level: intermediate

    3500:   Notes:
    3501:   Any options set on the `SNES` object, including those set with `SNESSetFromOptions()` remain.

    3503:   Call this if you wish to reuse a `SNES` but with different size vectors

    3505:   Also calls the application context destroy routine set with `SNESSetComputeApplicationContext()`

    3507: .seealso: [](ch_snes), `SNES`, `SNESDestroy()`, `SNESCreate()`, `SNESSetUp()`, `SNESSolve()`
    3508: @*/
    3509: PetscErrorCode SNESReset(SNES snes)
    3510: {
    3511:   PetscFunctionBegin;
    3513:   if (snes->ops->ctxdestroy && snes->ctx) {
    3514:     PetscCallBack("SNES callback destroy application context", (*snes->ops->ctxdestroy)(&snes->ctx));
    3515:     snes->ctx = NULL;
    3516:   }
    3517:   if (snes->npc) PetscCall(SNESReset(snes->npc));

    3519:   PetscTryTypeMethod(snes, reset);
    3520:   if (snes->ksp) PetscCall(KSPReset(snes->ksp));

    3522:   if (snes->linesearch) PetscCall(SNESLineSearchReset(snes->linesearch));

    3524:   PetscCall(VecDestroy(&snes->vec_rhs));
    3525:   PetscCall(VecDestroy(&snes->vec_sol));
    3526:   PetscCall(VecDestroy(&snes->vec_sol_update));
    3527:   PetscCall(VecDestroy(&snes->vec_func));
    3528:   PetscCall(MatDestroy(&snes->jacobian));
    3529:   PetscCall(MatDestroy(&snes->jacobian_pre));
    3530:   PetscCall(MatDestroy(&snes->picard));
    3531:   PetscCall(VecDestroyVecs(snes->nwork, &snes->work));
    3532:   PetscCall(VecDestroyVecs(snes->nvwork, &snes->vwork));

    3534:   snes->alwayscomputesfinalresidual = PETSC_FALSE;

    3536:   snes->nwork = snes->nvwork = 0;
    3537:   snes->setupcalled          = PETSC_FALSE;
    3538:   PetscFunctionReturn(PETSC_SUCCESS);
    3539: }

    3541: /*@
    3542:   SNESConvergedReasonViewCancel - Clears all the reason view functions for a `SNES` object provided with `SNESConvergedReasonViewSet()` also
    3543:   removes the default viewer.

    3545:   Collective

    3547:   Input Parameter:
    3548: . snes - the nonlinear iterative solver context obtained from `SNESCreate()`

    3550:   Level: intermediate

    3552: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESDestroy()`, `SNESReset()`, `SNESConvergedReasonViewSet()`
    3553: @*/
    3554: PetscErrorCode SNESConvergedReasonViewCancel(SNES snes)
    3555: {
    3556:   PetscInt i;

    3558:   PetscFunctionBegin;
    3560:   for (i = 0; i < snes->numberreasonviews; i++) {
    3561:     if (snes->reasonviewdestroy[i]) PetscCall((*snes->reasonviewdestroy[i])(&snes->reasonviewcontext[i]));
    3562:   }
    3563:   snes->numberreasonviews = 0;
    3564:   PetscCall(PetscViewerDestroy(&snes->convergedreasonviewer));
    3565:   PetscFunctionReturn(PETSC_SUCCESS);
    3566: }

    3568: /*@
    3569:   SNESDestroy - Destroys the nonlinear solver context that was created
    3570:   with `SNESCreate()`.

    3572:   Collective

    3574:   Input Parameter:
    3575: . snes - the `SNES` context

    3577:   Level: beginner

    3579: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESSolve()`
    3580: @*/
    3581: PetscErrorCode SNESDestroy(SNES *snes)
    3582: {
    3583:   DM dm;

    3585:   PetscFunctionBegin;
    3586:   if (!*snes) PetscFunctionReturn(PETSC_SUCCESS);
    3588:   if (--((PetscObject)*snes)->refct > 0) {
    3589:     *snes = NULL;
    3590:     PetscFunctionReturn(PETSC_SUCCESS);
    3591:   }

    3593:   PetscCall(SNESReset(*snes));
    3594:   PetscCall(SNESDestroy(&(*snes)->npc));

    3596:   /* if memory was published with SAWs then destroy it */
    3597:   PetscCall(PetscObjectSAWsViewOff((PetscObject)*snes));
    3598:   PetscTryTypeMethod(*snes, destroy);

    3600:   dm = (*snes)->dm;
    3601:   while (dm) {
    3602:     PetscCall(DMCoarsenHookRemove(dm, DMCoarsenHook_SNESVecSol, DMRestrictHook_SNESVecSol, *snes));
    3603:     PetscCall(DMGetCoarseDM(dm, &dm));
    3604:   }

    3606:   PetscCall(DMDestroy(&(*snes)->dm));
    3607:   PetscCall(KSPDestroy(&(*snes)->ksp));
    3608:   PetscCall(SNESLineSearchDestroy(&(*snes)->linesearch));

    3610:   PetscCall(PetscFree((*snes)->kspconvctx));
    3611:   if ((*snes)->ops->convergeddestroy) PetscCall((*(*snes)->ops->convergeddestroy)(&(*snes)->cnvP));
    3612:   if ((*snes)->conv_hist_alloc) PetscCall(PetscFree2((*snes)->conv_hist, (*snes)->conv_hist_its));
    3613:   PetscCall(SNESMonitorCancel(*snes));
    3614:   PetscCall(SNESConvergedReasonViewCancel(*snes));
    3615:   PetscCall(PetscHeaderDestroy(snes));
    3616:   PetscFunctionReturn(PETSC_SUCCESS);
    3617: }

    3619: /* ----------- Routines to set solver parameters ---------- */

    3621: /*@
    3622:   SNESSetLagPreconditioner - Sets when the preconditioner is rebuilt in the nonlinear solve `SNESSolve()`.

    3624:   Logically Collective

    3626:   Input Parameters:
    3627: + snes - the `SNES` context
    3628: - lag  - 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time
    3629:          the Jacobian is built etc. -2 indicates rebuild preconditioner at next chance but then never rebuild after that

    3631:   Options Database Keys:
    3632: + -snes_lag_jacobian_persists (true|false)       - sets the persistence through multiple `SNESSolve()`
    3633: . -snes_lag_jacobian (-2|1|2|...)                - sets the lag
    3634: . -snes_lag_preconditioner_persists (true|false) - sets the persistence through multiple `SNESSolve()`
    3635: - -snes_lag_preconditioner (-2|1|2|...)          - sets the lag

    3637:   Level: intermediate

    3639:   Notes:
    3640:   The default is 1

    3642:   The preconditioner is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1 or `SNESSetLagPreconditionerPersists()` was called

    3644:   `SNESSetLagPreconditionerPersists()` allows using the same uniform lagging (for example every second linear solve) across multiple nonlinear solves.

    3646: .seealso: [](ch_snes), `SNESGetLagPreconditioner()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESSetLagPreconditionerPersists()`,
    3647:           `SNESSetLagJacobianPersists()`, `SNES`, `SNESSolve()`
    3648: @*/
    3649: PetscErrorCode SNESSetLagPreconditioner(SNES snes, PetscInt lag)
    3650: {
    3651:   PetscFunctionBegin;
    3653:   PetscCheck(lag >= -2, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Lag must be -2, -1, 1 or greater");
    3654:   PetscCheck(lag, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Lag cannot be 0");
    3656:   snes->lagpreconditioner = lag;
    3657:   PetscFunctionReturn(PETSC_SUCCESS);
    3658: }

    3660: /*@
    3661:   SNESSetGridSequence - sets the number of steps of grid sequencing that `SNES` will do

    3663:   Logically Collective

    3665:   Input Parameters:
    3666: + snes  - the `SNES` context
    3667: - steps - the number of refinements to do, defaults to 0

    3669:   Options Database Key:
    3670: . -snes_grid_sequence steps - Use grid sequencing to generate initial guess

    3672:   Level: intermediate

    3674:   Notes:
    3675:   Once grid sequencing is turned on `SNESSolve()` will automatically perform the solve on each grid refinement.

    3677:   Use `SNESGetSolution()` to extract the fine grid solution after grid sequencing.

    3679: .seealso: [](ch_snes), `SNES`, `SNESGetLagPreconditioner()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESGetGridSequence()`,
    3680:           `SNESSetDM()`, `SNESSolve()`
    3681: @*/
    3682: PetscErrorCode SNESSetGridSequence(SNES snes, PetscInt steps)
    3683: {
    3684:   PetscFunctionBegin;
    3687:   snes->gridsequence = steps;
    3688:   PetscFunctionReturn(PETSC_SUCCESS);
    3689: }

    3691: /*@
    3692:   SNESGetGridSequence - gets the number of steps of grid sequencing that `SNES` will do

    3694:   Logically Collective

    3696:   Input Parameter:
    3697: . snes - the `SNES` context

    3699:   Output Parameter:
    3700: . steps - the number of refinements to do, defaults to 0

    3702:   Level: intermediate

    3704: .seealso: [](ch_snes), `SNESGetLagPreconditioner()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESSetGridSequence()`
    3705: @*/
    3706: PetscErrorCode SNESGetGridSequence(SNES snes, PetscInt *steps)
    3707: {
    3708:   PetscFunctionBegin;
    3710:   *steps = snes->gridsequence;
    3711:   PetscFunctionReturn(PETSC_SUCCESS);
    3712: }

    3714: /*@
    3715:   SNESGetLagPreconditioner - Return how often the preconditioner is rebuilt

    3717:   Not Collective

    3719:   Input Parameter:
    3720: . snes - the `SNES` context

    3722:   Output Parameter:
    3723: . lag - -1 indicates NEVER rebuild, 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time
    3724:          the Jacobian is built etc. -2 indicates rebuild preconditioner at next chance but then never rebuild after that

    3726:   Level: intermediate

    3728:   Notes:
    3729:   The default is 1

    3731:   The preconditioner is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1

    3733: .seealso: [](ch_snes), `SNES`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobianPersists()`, `SNESSetLagPreconditionerPersists()`
    3734: @*/
    3735: PetscErrorCode SNESGetLagPreconditioner(SNES snes, PetscInt *lag)
    3736: {
    3737:   PetscFunctionBegin;
    3739:   *lag = snes->lagpreconditioner;
    3740:   PetscFunctionReturn(PETSC_SUCCESS);
    3741: }

    3743: /*@
    3744:   SNESSetLagJacobian - Set when the Jacobian is rebuilt in the nonlinear solve. See `SNESSetLagPreconditioner()` for determining how
    3745:   often the preconditioner is rebuilt.

    3747:   Logically Collective

    3749:   Input Parameters:
    3750: + snes - the `SNES` context
    3751: - lag  - -1 indicates NEVER rebuild, 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time
    3752:          the Jacobian is built etc. -2 means rebuild at next chance but then never again

    3754:   Options Database Keys:
    3755: + -snes_lag_jacobian_persists (true|false)       - sets the persistence through multiple SNES solves
    3756: . -snes_lag_jacobian (-2|1|2|...)                - sets the lag
    3757: . -snes_lag_preconditioner_persists (true|false) - sets the persistence through multiple SNES solves
    3758: - -snes_lag_preconditioner (-2|1|2|...)          - sets the lag.

    3760:   Level: intermediate

    3762:   Notes:
    3763:   The default is 1

    3765:   The Jacobian is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1

    3767:   If  -1 is used before the very first nonlinear solve the CODE WILL FAIL! because no Jacobian is used, use -2 to indicate you want it recomputed
    3768:   at the next Newton step but never again (unless it is reset to another value)

    3770: .seealso: [](ch_snes), `SNES`, `SNESGetLagPreconditioner()`, `SNESSetLagPreconditioner()`, `SNESGetLagJacobianPersists()`, `SNESSetLagPreconditionerPersists()`
    3771: @*/
    3772: PetscErrorCode SNESSetLagJacobian(SNES snes, PetscInt lag)
    3773: {
    3774:   PetscFunctionBegin;
    3776:   PetscCheck(lag >= -2, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Lag must be -2, -1, 1 or greater");
    3777:   PetscCheck(lag, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Lag cannot be 0");
    3779:   snes->lagjacobian = lag;
    3780:   PetscFunctionReturn(PETSC_SUCCESS);
    3781: }

    3783: /*@
    3784:   SNESGetLagJacobian - Get how often the Jacobian is rebuilt. See `SNESGetLagPreconditioner()` to determine when the preconditioner is rebuilt

    3786:   Not Collective

    3788:   Input Parameter:
    3789: . snes - the `SNES` context

    3791:   Output Parameter:
    3792: . lag - -1 indicates NEVER rebuild, 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time
    3793:          the Jacobian is built etc.

    3795:   Level: intermediate

    3797:   Notes:
    3798:   The default is 1

    3800:   The jacobian is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1 or `SNESSetLagJacobianPersists()` was called.

    3802: .seealso: [](ch_snes), `SNES`, `SNESSetLagJacobian()`, `SNESSetLagPreconditioner()`, `SNESGetLagPreconditioner()`, `SNESSetLagJacobianPersists()`, `SNESSetLagPreconditionerPersists()`
    3803: @*/
    3804: PetscErrorCode SNESGetLagJacobian(SNES snes, PetscInt *lag)
    3805: {
    3806:   PetscFunctionBegin;
    3808:   *lag = snes->lagjacobian;
    3809:   PetscFunctionReturn(PETSC_SUCCESS);
    3810: }

    3812: /*@
    3813:   SNESSetLagJacobianPersists - Set whether or not the Jacobian lagging persists through multiple nonlinear solves

    3815:   Logically collective

    3817:   Input Parameters:
    3818: + snes - the `SNES` context
    3819: - flg  - jacobian lagging persists if true

    3821:   Options Database Keys:
    3822: + -snes_lag_jacobian_persists (true|false)       - sets the persistence through multiple SNES solves
    3823: . -snes_lag_jacobian (-2|1|2|...)                - sets the lag
    3824: . -snes_lag_preconditioner_persists (true|false) - sets the persistence through multiple SNES solves
    3825: - -snes_lag_preconditioner (-2|1|2|...)          - sets the lag

    3827:   Level: advanced

    3829:   Notes:
    3830:   Normally when `SNESSetLagJacobian()` is used, the Jacobian is always rebuilt at the beginning of each new nonlinear solve, this removes that behavior

    3832:   This is useful both for nonlinear preconditioning, where it's appropriate to have the Jacobian be stale by
    3833:   several solves, and for implicit time-stepping, where Jacobian lagging in the inner nonlinear solve over several
    3834:   timesteps may present huge efficiency gains.

    3836: .seealso: [](ch_snes), `SNES`, `SNESSetLagPreconditionerPersists()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESGetNPC()`
    3837: @*/
    3838: PetscErrorCode SNESSetLagJacobianPersists(SNES snes, PetscBool flg)
    3839: {
    3840:   PetscFunctionBegin;
    3843:   snes->lagjac_persist = flg;
    3844:   PetscFunctionReturn(PETSC_SUCCESS);
    3845: }

    3847: /*@
    3848:   SNESSetLagPreconditionerPersists - Set whether or not the preconditioner lagging persists through multiple nonlinear solves

    3850:   Logically Collective

    3852:   Input Parameters:
    3853: + snes - the `SNES` context
    3854: - flg  - preconditioner lagging persists if true

    3856:   Options Database Keys:
    3857: + -snes_lag_jacobian_persists (true|false)       - sets the persistence through multiple SNES solves
    3858: . -snes_lag_jacobian (-2|1|2|...)                - sets the lag
    3859: . -snes_lag_preconditioner_persists (true|false) - sets the persistence through multiple SNES solves
    3860: - -snes_lag_preconditioner (-2|1|2|...)          - sets the lag

    3862:   Level: developer

    3864:   Notes:
    3865:   Normally when `SNESSetLagPreconditioner()` is used, the preconditioner is always rebuilt at the beginning of each new nonlinear solve, this removes that behavior

    3867:   This is useful both for nonlinear preconditioning, where it's appropriate to have the preconditioner be stale
    3868:   by several solves, and for implicit time-stepping, where preconditioner lagging in the inner nonlinear solve over
    3869:   several timesteps may present huge efficiency gains.

    3871: .seealso: [](ch_snes), `SNES`, `SNESSetLagJacobianPersists()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESGetNPC()`, `SNESSetLagPreconditioner()`
    3872: @*/
    3873: PetscErrorCode SNESSetLagPreconditionerPersists(SNES snes, PetscBool flg)
    3874: {
    3875:   PetscFunctionBegin;
    3878:   snes->lagpre_persist = flg;
    3879:   PetscFunctionReturn(PETSC_SUCCESS);
    3880: }

    3882: /*@
    3883:   SNESSetForceIteration - force `SNESSolve()` to take at least one iteration regardless of the initial residual norm

    3885:   Logically Collective

    3887:   Input Parameters:
    3888: + snes  - the `SNES` context
    3889: - force - `PETSC_TRUE` require at least one iteration

    3891:   Options Database Key:
    3892: . -snes_force_iteration force - Sets forcing an iteration

    3894:   Level: intermediate

    3896:   Note:
    3897:   This is used sometimes with `TS` to prevent `TS` from detecting a false steady state solution

    3899: .seealso: [](ch_snes), `SNES`, `TS`, `SNESSetDivergenceTolerance()`
    3900: @*/
    3901: PetscErrorCode SNESSetForceIteration(SNES snes, PetscBool force)
    3902: {
    3903:   PetscFunctionBegin;
    3905:   snes->forceiteration = force;
    3906:   PetscFunctionReturn(PETSC_SUCCESS);
    3907: }

    3909: /*@
    3910:   SNESGetForceIteration - Check whether or not `SNESSolve()` take at least one iteration regardless of the initial residual norm

    3912:   Logically Collective

    3914:   Input Parameter:
    3915: . snes - the `SNES` context

    3917:   Output Parameter:
    3918: . force - `PETSC_TRUE` requires at least one iteration.

    3920:   Level: intermediate

    3922: .seealso: [](ch_snes), `SNES`, `SNESSetForceIteration()`, `SNESSetDivergenceTolerance()`
    3923: @*/
    3924: PetscErrorCode SNESGetForceIteration(SNES snes, PetscBool *force)
    3925: {
    3926:   PetscFunctionBegin;
    3928:   *force = snes->forceiteration;
    3929:   PetscFunctionReturn(PETSC_SUCCESS);
    3930: }

    3932: /*@
    3933:   SNESSetTolerances - Sets various parameters used in `SNES` convergence tests.

    3935:   Logically Collective

    3937:   Input Parameters:
    3938: + snes   - the `SNES` context
    3939: . abstol - the absolute convergence tolerance, $ F(x^n) \le abstol $
    3940: . rtol   - the relative convergence tolerance, $ F(x^n) \le reltol * F(x^0) $
    3941: . stol   - convergence tolerance in terms of the norm of the change in the solution between steps,  || delta x || < stol*|| x ||
    3942: . maxit  - the maximum number of iterations allowed in the solver, default 50.
    3943: - maxf   - the maximum number of function evaluations allowed in the solver (use `PETSC_UNLIMITED` indicates no limit), default 10,000

    3945:   Options Database Keys:
    3946: + -snes_atol abstol    - Sets `abstol`
    3947: . -snes_rtol rtol      - Sets `rtol`
    3948: . -snes_stol stol      - Sets `stol`
    3949: . -snes_max_it maxit   - Sets `maxit`
    3950: - -snes_max_funcs maxf - Sets `maxf` (use `unlimited` to have no maximum)

    3952:   Level: intermediate

    3954:   Note:
    3955:   All parameters must be non-negative

    3957:   Use `PETSC_CURRENT` to retain the current value of any parameter and `PETSC_DETERMINE` to use the default value for the given `SNES`.
    3958:   The default value is the value in the object when its type is set.

    3960:   Use `PETSC_UNLIMITED` on `maxit` or `maxf` to indicate there is no bound on the number of iterations or number of function evaluations.

    3962:   Fortran Note:
    3963:   Use `PETSC_CURRENT_INTEGER`, `PETSC_CURRENT_REAL`, `PETSC_UNLIMITED_INTEGER`, `PETSC_DETERMINE_INTEGER`, or `PETSC_DETERMINE_REAL`

    3965: .seealso: [](ch_snes), `SNESSolve()`, `SNES`, `SNESSetDivergenceTolerance()`, `SNESSetForceIteration()`
    3966: @*/
    3967: PetscErrorCode SNESSetTolerances(SNES snes, PetscReal abstol, PetscReal rtol, PetscReal stol, PetscInt maxit, PetscInt maxf)
    3968: {
    3969:   PetscFunctionBegin;

    3977:   if (abstol == (PetscReal)PETSC_DETERMINE) {
    3978:     snes->abstol = snes->default_abstol;
    3979:   } else if (abstol != (PetscReal)PETSC_CURRENT) {
    3980:     PetscCheck(abstol >= 0.0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Absolute tolerance %g must be non-negative", (double)abstol);
    3981:     snes->abstol = abstol;
    3982:   }

    3984:   if (rtol == (PetscReal)PETSC_DETERMINE) {
    3985:     snes->rtol = snes->default_rtol;
    3986:   } else if (rtol != (PetscReal)PETSC_CURRENT) {
    3987:     PetscCheck(rtol >= 0.0 && 1.0 > rtol, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Relative tolerance %g must be non-negative and less than 1.0", (double)rtol);
    3988:     snes->rtol = rtol;
    3989:   }

    3991:   if (stol == (PetscReal)PETSC_DETERMINE) {
    3992:     snes->stol = snes->default_stol;
    3993:   } else if (stol != (PetscReal)PETSC_CURRENT) {
    3994:     PetscCheck(stol >= 0.0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Step tolerance %g must be non-negative", (double)stol);
    3995:     snes->stol = stol;
    3996:   }

    3998:   if (maxit == PETSC_DETERMINE) {
    3999:     snes->max_its = snes->default_max_its;
    4000:   } else if (maxit == PETSC_UNLIMITED) {
    4001:     snes->max_its = PETSC_INT_MAX;
    4002:   } else if (maxit != PETSC_CURRENT) {
    4003:     PetscCheck(maxit >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Maximum number of iterations %" PetscInt_FMT " must be non-negative", maxit);
    4004:     snes->max_its = maxit;
    4005:   }

    4007:   if (maxf == PETSC_DETERMINE) {
    4008:     snes->max_funcs = snes->default_max_funcs;
    4009:   } else if (maxf == PETSC_UNLIMITED || maxf == -1) {
    4010:     snes->max_funcs = PETSC_UNLIMITED;
    4011:   } else if (maxf != PETSC_CURRENT) {
    4012:     PetscCheck(maxf >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Maximum number of function evaluations %" PetscInt_FMT " must be nonnegative", maxf);
    4013:     snes->max_funcs = maxf;
    4014:   }
    4015:   PetscFunctionReturn(PETSC_SUCCESS);
    4016: }

    4018: /*@
    4019:   SNESSetDivergenceTolerance - Sets the divergence tolerance used for the `SNES` divergence test.

    4021:   Logically Collective

    4023:   Input Parameters:
    4024: + snes   - the `SNES` context
    4025: - divtol - the divergence tolerance. Use `PETSC_UNLIMITED` to deactivate the test. If the residual norm $ F(x^n) \ge divtol * F(x^0) $ the solver
    4026:            is stopped due to divergence.

    4028:   Options Database Key:
    4029: . -snes_divergence_tolerance divtol - Sets `divtol`

    4031:   Level: intermediate

    4033:   Notes:
    4034:   Use `PETSC_DETERMINE` to use the default value from when the object's type was set.

    4036:   Fortran Note:
    4037:   Use ``PETSC_DETERMINE_REAL` or `PETSC_UNLIMITED_REAL`

    4039: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetTolerances()`, `SNESGetDivergenceTolerance()`
    4040: @*/
    4041: PetscErrorCode SNESSetDivergenceTolerance(SNES snes, PetscReal divtol)
    4042: {
    4043:   PetscFunctionBegin;

    4047:   if (divtol == (PetscReal)PETSC_DETERMINE) {
    4048:     snes->divtol = snes->default_divtol;
    4049:   } else if (divtol == (PetscReal)PETSC_UNLIMITED || divtol == -1) {
    4050:     snes->divtol = PETSC_UNLIMITED;
    4051:   } else if (divtol != (PetscReal)PETSC_CURRENT) {
    4052:     PetscCheck(divtol >= 1.0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Divergence tolerance %g must be greater than 1.0", (double)divtol);
    4053:     snes->divtol = divtol;
    4054:   }
    4055:   PetscFunctionReturn(PETSC_SUCCESS);
    4056: }

    4058: /*@
    4059:   SNESGetTolerances - Gets various parameters used in `SNES` convergence tests.

    4061:   Not Collective

    4063:   Input Parameter:
    4064: . snes - the `SNES` context

    4066:   Output Parameters:
    4067: + atol  - the absolute convergence tolerance
    4068: . rtol  - the relative convergence tolerance
    4069: . stol  - convergence tolerance in terms of the norm of the change in the solution between steps
    4070: . maxit - the maximum number of iterations allowed
    4071: - maxf  - the maximum number of function evaluations allowed, `PETSC_UNLIMITED` indicates no bound

    4073:   Level: intermediate

    4075:   Notes:
    4076:   See `SNESSetTolerances()` for details on the parameters.

    4078:   The user can specify `NULL` for any parameter that is not needed.

    4080: .seealso: [](ch_snes), `SNES`, `SNESSetTolerances()`
    4081: @*/
    4082: PetscErrorCode SNESGetTolerances(SNES snes, PetscReal *atol, PetscReal *rtol, PetscReal *stol, PetscInt *maxit, PetscInt *maxf)
    4083: {
    4084:   PetscFunctionBegin;
    4086:   if (atol) *atol = snes->abstol;
    4087:   if (rtol) *rtol = snes->rtol;
    4088:   if (stol) *stol = snes->stol;
    4089:   if (maxit) *maxit = snes->max_its;
    4090:   if (maxf) *maxf = snes->max_funcs;
    4091:   PetscFunctionReturn(PETSC_SUCCESS);
    4092: }

    4094: /*@
    4095:   SNESGetDivergenceTolerance - Gets divergence tolerance used in divergence test.

    4097:   Not Collective

    4099:   Input Parameters:
    4100: + snes   - the `SNES` context
    4101: - divtol - divergence tolerance

    4103:   Level: intermediate

    4105: .seealso: [](ch_snes), `SNES`, `SNESSetDivergenceTolerance()`
    4106: @*/
    4107: PetscErrorCode SNESGetDivergenceTolerance(SNES snes, PetscReal *divtol)
    4108: {
    4109:   PetscFunctionBegin;
    4111:   if (divtol) *divtol = snes->divtol;
    4112:   PetscFunctionReturn(PETSC_SUCCESS);
    4113: }

    4115: PETSC_INTERN PetscErrorCode SNESMonitorRange_Private(SNES, PetscInt, PetscReal *);

    4117: /*@C
    4118:   SNESMonitorLGRange - Line-graph monitor that plots the residual norm together with residual-range statistics for a `SNESSolve()`

    4120:   Collective

    4122:   Input Parameters:
    4123: + snes   - the `SNES` context
    4124: . n      - the iteration number
    4125: . rnorm  - the 2-norm of the residual
    4126: - monctx - a `PetscViewer` of type `PETSCVIEWERDRAW` set up with `PetscViewerMonitorLGSetUp()`

    4128:   Level: intermediate

    4130:   Note:
    4131:   Plots four line graphs in the viewer: the residual norm (log scale), the fraction of residual entries larger than 20% of the maximum entry, the relative decrease `(prev - rnorm)/prev`, and their product.

    4133: .seealso: [](ch_snes), `SNES`, `SNESMonitorSet()`, `SNESMonitorDefault()`, `PetscViewerDrawGetDrawLG()`, `PetscDrawLG`
    4134: @*/
    4135: PetscErrorCode SNESMonitorLGRange(SNES snes, PetscInt n, PetscReal rnorm, PetscCtx monctx)
    4136: {
    4137:   PetscDrawLG      lg;
    4138:   PetscReal        x, y, per;
    4139:   PetscViewer      v = (PetscViewer)monctx;
    4140:   static PetscReal prev; /* should be in the context */
    4141:   PetscDraw        draw;

    4143:   PetscFunctionBegin;
    4145:   PetscCall(PetscViewerDrawGetDrawLG(v, 0, &lg));
    4146:   if (!n) PetscCall(PetscDrawLGReset(lg));
    4147:   PetscCall(PetscDrawLGGetDraw(lg, &draw));
    4148:   PetscCall(PetscDrawSetTitle(draw, "Residual norm"));
    4149:   x = (PetscReal)n;
    4150:   if (rnorm > 0.0) y = PetscLog10Real(rnorm);
    4151:   else y = -15.0;
    4152:   PetscCall(PetscDrawLGAddPoint(lg, &x, &y));
    4153:   if (n < 20 || !(n % 5) || snes->reason) {
    4154:     PetscCall(PetscDrawLGDraw(lg));
    4155:     PetscCall(PetscDrawLGSave(lg));
    4156:   }

    4158:   PetscCall(PetscViewerDrawGetDrawLG(v, 1, &lg));
    4159:   if (!n) PetscCall(PetscDrawLGReset(lg));
    4160:   PetscCall(PetscDrawLGGetDraw(lg, &draw));
    4161:   PetscCall(PetscDrawSetTitle(draw, "% elements > .2*max element"));
    4162:   PetscCall(SNESMonitorRange_Private(snes, n, &per));
    4163:   x = (PetscReal)n;
    4164:   y = 100.0 * per;
    4165:   PetscCall(PetscDrawLGAddPoint(lg, &x, &y));
    4166:   if (n < 20 || !(n % 5) || snes->reason) {
    4167:     PetscCall(PetscDrawLGDraw(lg));
    4168:     PetscCall(PetscDrawLGSave(lg));
    4169:   }

    4171:   PetscCall(PetscViewerDrawGetDrawLG(v, 2, &lg));
    4172:   if (!n) {
    4173:     prev = rnorm;
    4174:     PetscCall(PetscDrawLGReset(lg));
    4175:   }
    4176:   PetscCall(PetscDrawLGGetDraw(lg, &draw));
    4177:   PetscCall(PetscDrawSetTitle(draw, "(norm -oldnorm)/oldnorm"));
    4178:   x = (PetscReal)n;
    4179:   y = (prev - rnorm) / prev;
    4180:   PetscCall(PetscDrawLGAddPoint(lg, &x, &y));
    4181:   if (n < 20 || !(n % 5) || snes->reason) {
    4182:     PetscCall(PetscDrawLGDraw(lg));
    4183:     PetscCall(PetscDrawLGSave(lg));
    4184:   }

    4186:   PetscCall(PetscViewerDrawGetDrawLG(v, 3, &lg));
    4187:   if (!n) PetscCall(PetscDrawLGReset(lg));
    4188:   PetscCall(PetscDrawLGGetDraw(lg, &draw));
    4189:   PetscCall(PetscDrawSetTitle(draw, "(norm -oldnorm)/oldnorm*(% > .2 max)"));
    4190:   x = (PetscReal)n;
    4191:   y = (prev - rnorm) / (prev * per);
    4192:   if (n > 2) { /*skip initial crazy value */
    4193:     PetscCall(PetscDrawLGAddPoint(lg, &x, &y));
    4194:   }
    4195:   if (n < 20 || !(n % 5) || snes->reason) {
    4196:     PetscCall(PetscDrawLGDraw(lg));
    4197:     PetscCall(PetscDrawLGSave(lg));
    4198:   }
    4199:   prev = rnorm;
    4200:   PetscFunctionReturn(PETSC_SUCCESS);
    4201: }

    4203: /*@
    4204:   SNESConverged - Run the convergence test and update the `SNESConvergedReason`.

    4206:   Collective

    4208:   Input Parameters:
    4209: + snes  - the `SNES` context
    4210: . it    - current iteration
    4211: . xnorm - 2-norm of current iterate
    4212: . snorm - 2-norm of current step
    4213: - fnorm - 2-norm of function

    4215:   Level: developer

    4217:   Note:
    4218:   This routine is called by the `SNESSolve()` implementations.
    4219:   It does not typically need to be called by the user.

    4221: .seealso: [](ch_snes), `SNES`, `SNESSolve`, `SNESSetConvergenceTest()`
    4222: @*/
    4223: PetscErrorCode SNESConverged(SNES snes, PetscInt it, PetscReal xnorm, PetscReal snorm, PetscReal fnorm)
    4224: {
    4225:   PetscFunctionBegin;
    4226:   if (!snes->reason) {
    4227:     if (snes->normschedule == SNES_NORM_ALWAYS) PetscUseTypeMethod(snes, converged, it, xnorm, snorm, fnorm, &snes->reason, snes->cnvP);
    4228:     if (it == snes->max_its && !snes->reason) {
    4229:       if (snes->normschedule == SNES_NORM_ALWAYS) {
    4230:         PetscCall(PetscInfo(snes, "Maximum number of iterations has been reached: %" PetscInt_FMT "\n", snes->max_its));
    4231:         snes->reason = SNES_DIVERGED_MAX_IT;
    4232:       } else snes->reason = SNES_CONVERGED_ITS;
    4233:     }
    4234:   }
    4235:   PetscFunctionReturn(PETSC_SUCCESS);
    4236: }

    4238: /*@
    4239:   SNESMonitor - runs any `SNES` monitor routines provided with `SNESMonitor()` or the options database

    4241:   Collective

    4243:   Input Parameters:
    4244: + snes  - nonlinear solver context obtained from `SNESCreate()`
    4245: . iter  - current iteration number
    4246: - rnorm - current relative norm of the residual

    4248:   Level: developer

    4250:   Note:
    4251:   This routine is called by the `SNESSolve()` implementations.
    4252:   It does not typically need to be called by the user.

    4254: .seealso: [](ch_snes), `SNES`, `SNESMonitorSet()`
    4255: @*/
    4256: PetscErrorCode SNESMonitor(SNES snes, PetscInt iter, PetscReal rnorm)
    4257: {
    4258:   PetscInt i, n = snes->numbermonitors;

    4260:   PetscFunctionBegin;
    4261:   PetscCall(VecLockReadPush(snes->vec_sol));
    4262:   for (i = 0; i < n; i++) PetscCall((*snes->monitor[i])(snes, iter, rnorm, snes->monitorcontext[i]));
    4263:   PetscCall(VecLockReadPop(snes->vec_sol));
    4264:   PetscFunctionReturn(PETSC_SUCCESS);
    4265: }

    4267: /* ------------ Routines to set performance monitoring options ----------- */

    4269: /*MC
    4270:     SNESMonitorFunction - functional form passed to `SNESMonitorSet()` to monitor convergence of nonlinear solver

    4272:      Synopsis:
    4273: #include <petscsnes.h>
    4274:     PetscErrorCode SNESMonitorFunction(SNES snes, PetscInt its, PetscReal norm, PetscCtx mctx)

    4276:      Collective

    4278:     Input Parameters:
    4279: +    snes - the `SNES` context
    4280: .    its - iteration number
    4281: .    norm - 2-norm function value (may be estimated)
    4282: -    mctx - [optional] monitoring context

    4284:    Level: advanced

    4286: .seealso: [](ch_snes), `SNESMonitorSet()`, `PetscCtx`
    4287: M*/

    4289: /*@C
    4290:   SNESMonitorSet - Sets an ADDITIONAL function that is to be used at every
    4291:   iteration of the `SNES` nonlinear solver to display the iteration's
    4292:   progress.

    4294:   Logically Collective

    4296:   Input Parameters:
    4297: + snes           - the `SNES` context
    4298: . f              - the monitor function,  for the calling sequence see `SNESMonitorFunction`
    4299: . mctx           - [optional] user-defined context for private data for the monitor routine (use `NULL` if no context is desired)
    4300: - monitordestroy - [optional] routine that frees monitor context (may be `NULL`), see `PetscCtxDestroyFn` for the calling sequence

    4302:   Calling sequence of f:
    4303: + snes  - the `SNES` object
    4304: . it    - the current iteration
    4305: . rnorm - norm of the residual
    4306: - mctx  - the optional monitor context

    4308:   Options Database Keys:
    4309: + -snes_monitor               - sets `SNESMonitorDefault()`
    4310: . -snes_monitor draw::draw_lg - sets line graph monitor
    4311: - -snes_monitor_cancel        - cancels all monitors that have been hardwired into a code by calls to `SNESMonitorSet()`, but does not cancel those set via
    4312:                                 the options database.

    4314:   Level: intermediate

    4316:   Note:
    4317:   Several different monitoring routines may be set by calling
    4318:   `SNESMonitorSet()` multiple times; all will be called in the
    4319:   order in which they were set.

    4321:   Fortran Note:
    4322:   Only a single monitor function can be set for each `SNES` object

    4324: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESMonitorDefault()`, `SNESMonitorCancel()`, `SNESMonitorFunction`, `PetscCtxDestroyFn`
    4325: @*/
    4326: PetscErrorCode SNESMonitorSet(SNES snes, PetscErrorCode (*f)(SNES snes, PetscInt it, PetscReal rnorm, PetscCtx mctx), PetscCtx mctx, PetscCtxDestroyFn *monitordestroy)
    4327: {
    4328:   PetscFunctionBegin;
    4330:   for (PetscInt i = 0; i < snes->numbermonitors; i++) {
    4331:     PetscBool identical;

    4333:     PetscCall(PetscMonitorCompare((PetscErrorCode (*)(void))(PetscVoidFn *)f, mctx, monitordestroy, (PetscErrorCode (*)(void))(PetscVoidFn *)snes->monitor[i], snes->monitorcontext[i], snes->monitordestroy[i], &identical));
    4334:     if (identical) PetscFunctionReturn(PETSC_SUCCESS);
    4335:   }
    4336:   PetscCheck(snes->numbermonitors < MAXSNESMONITORS, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Too many monitors set");
    4337:   snes->monitor[snes->numbermonitors]          = f;
    4338:   snes->monitordestroy[snes->numbermonitors]   = monitordestroy;
    4339:   snes->monitorcontext[snes->numbermonitors++] = mctx;
    4340:   PetscFunctionReturn(PETSC_SUCCESS);
    4341: }

    4343: /*@
    4344:   SNESMonitorCancel - Clears all the monitor functions for a `SNES` object.

    4346:   Logically Collective

    4348:   Input Parameter:
    4349: . snes - the `SNES` context

    4351:   Options Database Key:
    4352: . -snes_monitor_cancel - cancels all monitors that have been hardwired
    4353:                          into a code by calls to `SNESMonitorSet()`, but does not cancel those
    4354:                          set via the options database

    4356:   Level: intermediate

    4358:   Note:
    4359:   There is no way to clear one specific monitor from a `SNES` object.

    4361: .seealso: [](ch_snes), `SNES`, `SNESMonitorDefault()`, `SNESMonitorSet()`
    4362: @*/
    4363: PetscErrorCode SNESMonitorCancel(SNES snes)
    4364: {
    4365:   PetscInt i;

    4367:   PetscFunctionBegin;
    4369:   for (i = 0; i < snes->numbermonitors; i++) {
    4370:     if (snes->monitordestroy[i]) PetscCall((*snes->monitordestroy[i])(&snes->monitorcontext[i]));
    4371:   }
    4372:   snes->numbermonitors = 0;
    4373:   PetscFunctionReturn(PETSC_SUCCESS);
    4374: }

    4376: /*@C
    4377:   SNESSetConvergenceTest - Sets the function that is to be used
    4378:   to test for convergence of the nonlinear iterative solution.

    4380:   Logically Collective

    4382:   Input Parameters:
    4383: + snes    - the `SNES` context
    4384: . func    - routine to test for convergence
    4385: . ctx     - [optional] context for private data for the convergence routine  (may be `NULL`)
    4386: - destroy - [optional] destructor for the context (may be `NULL`; `PETSC_NULL_FUNCTION` in Fortran)

    4388:   Calling sequence of func:
    4389: + snes   - the `SNES` context
    4390: . it     - the current iteration number
    4391: . xnorm  - the norm of the new solution
    4392: . snorm  - the norm of the step
    4393: . fnorm  - the norm of the function value
    4394: . reason - output, the reason convergence or divergence as declared
    4395: - ctx    - the optional convergence test context

    4397:   Level: advanced

    4399: .seealso: [](ch_snes), `SNES`, `SNESConvergedDefault()`, `SNESConvergedSkip()`
    4400: @*/
    4401: PetscErrorCode SNESSetConvergenceTest(SNES snes, PetscErrorCode (*func)(SNES snes, PetscInt it, PetscReal xnorm, PetscReal snorm, PetscReal fnorm, SNESConvergedReason *reason, PetscCtx ctx), PetscCtx ctx, PetscCtxDestroyFn *destroy)
    4402: {
    4403:   PetscFunctionBegin;
    4405:   if (!func) func = SNESConvergedSkip;
    4406:   if (snes->ops->convergeddestroy) PetscCall((*snes->ops->convergeddestroy)(&snes->cnvP));
    4407:   snes->ops->converged        = func;
    4408:   snes->ops->convergeddestroy = destroy;
    4409:   snes->cnvP                  = ctx;
    4410:   PetscFunctionReturn(PETSC_SUCCESS);
    4411: }

    4413: /*@
    4414:   SNESGetConvergedReason - Gets the reason the `SNES` iteration was stopped, which may be due to convergence, divergence, or stagnation

    4416:   Not Collective

    4418:   Input Parameter:
    4419: . snes - the `SNES` context

    4421:   Output Parameter:
    4422: . reason - negative value indicates diverged, positive value converged, see `SNESConvergedReason` for the individual convergence tests for complete lists

    4424:   Options Database Key:
    4425: . -snes_converged_reason - prints the reason to standard out

    4427:   Level: intermediate

    4429:   Note:
    4430:   Should only be called after the call the `SNESSolve()` is complete, if it is called earlier it returns the value `SNES__CONVERGED_ITERATING`.

    4432: .seealso: [](ch_snes), `SNESSolve()`, `SNESSetConvergenceTest()`, `SNESSetConvergedReason()`, `SNESConvergedReason`, `SNESGetConvergedReasonString()`
    4433: @*/
    4434: PetscErrorCode SNESGetConvergedReason(SNES snes, SNESConvergedReason *reason)
    4435: {
    4436:   PetscFunctionBegin;
    4438:   PetscAssertPointer(reason, 2);
    4439:   *reason = snes->reason;
    4440:   PetscFunctionReturn(PETSC_SUCCESS);
    4441: }

    4443: /*@C
    4444:   SNESGetConvergedReasonString - Return a human readable string for `SNESConvergedReason`

    4446:   Not Collective

    4448:   Input Parameter:
    4449: . snes - the `SNES` context

    4451:   Output Parameter:
    4452: . strreason - a human readable string that describes `SNES` converged reason

    4454:   Level: beginner

    4456: .seealso: [](ch_snes), `SNES`, `SNESGetConvergedReason()`
    4457: @*/
    4458: PetscErrorCode SNESGetConvergedReasonString(SNES snes, const char **strreason)
    4459: {
    4460:   PetscFunctionBegin;
    4462:   PetscAssertPointer(strreason, 2);
    4463:   *strreason = SNESConvergedReasons[snes->reason];
    4464:   PetscFunctionReturn(PETSC_SUCCESS);
    4465: }

    4467: /*@
    4468:   SNESSetConvergedReason - Sets the reason the `SNES` iteration was stopped.

    4470:   Not Collective

    4472:   Input Parameters:
    4473: + snes   - the `SNES` context
    4474: - reason - negative value indicates diverged, positive value converged, see `SNESConvergedReason` or the
    4475:             manual pages for the individual convergence tests for complete lists

    4477:   Level: developer

    4479:   Developer Note:
    4480:   Called inside the various `SNESSolve()` implementations

    4482: .seealso: [](ch_snes), `SNESGetConvergedReason()`, `SNESSetConvergenceTest()`, `SNESConvergedReason`
    4483: @*/
    4484: PetscErrorCode SNESSetConvergedReason(SNES snes, SNESConvergedReason reason)
    4485: {
    4486:   PetscFunctionBegin;
    4488:   PetscCheck(!snes->errorifnotconverged || reason > 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_PLIB, "SNES code should have previously errored due to negative reason");
    4489:   snes->reason = reason;
    4490:   PetscFunctionReturn(PETSC_SUCCESS);
    4491: }

    4493: /*@
    4494:   SNESSetConvergenceHistory - Sets the arrays used to hold the convergence history.

    4496:   Logically Collective

    4498:   Input Parameters:
    4499: + snes  - iterative context obtained from `SNESCreate()`
    4500: . a     - array to hold history, this array will contain the function norms computed at each step
    4501: . its   - integer array holds the number of linear iterations for each solve.
    4502: . na    - size of `a` and `its`
    4503: - reset - `PETSC_TRUE` indicates each new nonlinear solve resets the history counter to zero,
    4504:           else it continues storing new values for new nonlinear solves after the old ones

    4506:   Level: intermediate

    4508:   Notes:
    4509:   If 'a' and 'its' are `NULL` then space is allocated for the history. If 'na' is `PETSC_DECIDE` (or, deprecated, `PETSC_DEFAULT`) then a
    4510:   default array of length 1,000 is allocated.

    4512:   This routine is useful, e.g., when running a code for purposes
    4513:   of accurate performance monitoring, when no I/O should be done
    4514:   during the section of code that is being timed.

    4516:   If the arrays run out of space after a number of iterations then the later values are not saved in the history

    4518: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESGetConvergenceHistory()`
    4519: @*/
    4520: PetscErrorCode SNESSetConvergenceHistory(SNES snes, PetscReal a[], PetscInt its[], PetscInt na, PetscBool reset)
    4521: {
    4522:   PetscFunctionBegin;
    4524:   if (a) PetscAssertPointer(a, 2);
    4525:   if (its) PetscAssertPointer(its, 3);
    4526:   if (!a) {
    4527:     if (na == PETSC_DECIDE) na = 1000;
    4528:     PetscCall(PetscCalloc2(na, &a, na, &its));
    4529:     snes->conv_hist_alloc = PETSC_TRUE;
    4530:   }
    4531:   snes->conv_hist       = a;
    4532:   snes->conv_hist_its   = its;
    4533:   snes->conv_hist_max   = (size_t)na;
    4534:   snes->conv_hist_len   = 0;
    4535:   snes->conv_hist_reset = reset;
    4536:   PetscFunctionReturn(PETSC_SUCCESS);
    4537: }

    4539: #if defined(PETSC_HAVE_MATLAB)
    4540:   #include <engine.h> /* MATLAB include file */
    4541:   #include <mex.h>    /* MATLAB include file */

    4543: PETSC_EXTERN mxArray *SNESGetConvergenceHistoryMatlab(SNES snes)
    4544: {
    4545:   mxArray   *mat;
    4546:   PetscInt   i;
    4547:   PetscReal *ar;

    4549:   mat = mxCreateDoubleMatrix(snes->conv_hist_len, 1, mxREAL);
    4550:   ar  = (PetscReal *)mxGetData(mat);
    4551:   for (i = 0; i < snes->conv_hist_len; i++) ar[i] = snes->conv_hist[i];
    4552:   return mat;
    4553: }
    4554: #endif

    4556: /*@C
    4557:   SNESGetConvergenceHistory - Gets the arrays used to hold the convergence history.

    4559:   Not Collective

    4561:   Input Parameter:
    4562: . snes - iterative context obtained from `SNESCreate()`

    4564:   Output Parameters:
    4565: + a   - array to hold history, usually was set with `SNESSetConvergenceHistory()`
    4566: . its - integer array holds the number of linear iterations (or
    4567:          negative if not converged) for each solve.
    4568: - na  - size of `a` and `its`

    4570:   Level: intermediate

    4572:   Note:
    4573:   This routine is useful, e.g., when running a code for purposes
    4574:   of accurate performance monitoring, when no I/O should be done
    4575:   during the section of code that is being timed.

    4577:   Fortran Notes:
    4578:   Return the arrays with ``SNESRestoreConvergenceHistory()`

    4580:   Use the arguments
    4581: .vb
    4582:   PetscReal, pointer :: a(:)
    4583:   PetscInt, pointer :: its(:)
    4584: .ve

    4586: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetConvergenceHistory()`
    4587: @*/
    4588: PetscErrorCode SNESGetConvergenceHistory(SNES snes, PetscReal *a[], PetscInt *its[], PetscInt *na)
    4589: {
    4590:   PetscFunctionBegin;
    4592:   if (a) *a = snes->conv_hist;
    4593:   if (its) *its = snes->conv_hist_its;
    4594:   if (na) *na = (PetscInt)snes->conv_hist_len;
    4595:   PetscFunctionReturn(PETSC_SUCCESS);
    4596: }

    4598: /*@C
    4599:   SNESSetUpdate - Sets the general-purpose update function called
    4600:   at the beginning of every iteration of the nonlinear solve. Specifically
    4601:   it is called just before the Jacobian is "evaluated" and after the function
    4602:   evaluation.

    4604:   Logically Collective

    4606:   Input Parameters:
    4607: + snes - The nonlinear solver context
    4608: - func - The update function; for calling sequence see `SNESUpdateFn`

    4610:   Level: advanced

    4612:   Notes:
    4613:   This is NOT what one uses to update the ghost points before a function evaluation, that should be done at the beginning of your function provided
    4614:   to `SNESSetFunction()`, or `SNESSetPicard()`
    4615:   This is not used by most users, and it is intended to provide a general hook that is run
    4616:   right before the direction step is computed.

    4618:   Users are free to modify the current residual vector,
    4619:   the current linearization point, or any other vector associated to the specific solver used.
    4620:   If such modifications take place, it is the user responsibility to update all the relevant
    4621:   vectors. For example, if one is adjusting the model parameters at each Newton step their code may look like
    4622: .vb
    4623:   PetscErrorCode update(SNES snes, PetscInt iteration)
    4624:   {
    4625:     PetscFunctionBeginUser;
    4626:     if (iteration > 0) {
    4627:       // update the model parameters here
    4628:       Vec x,f;
    4629:       PetscCall(SNESGetSolution(snes,&x));
    4630:       PetcCall(SNESGetFunction(snes,&f,NULL,NULL));
    4631:       PetscCall(SNESComputeFunction(snes,x,f));
    4632:     }
    4633:     PetscFunctionReturn(PETSC_SUCCESS);
    4634:   }
    4635: .ve

    4637:   There are a variety of function hooks one many set that are called at different stages of the nonlinear solution process, see the functions listed below.

    4639: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetJacobian()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`, `SNESNewtonTRSetPreCheck()`, `SNESNewtonTRSetPostCheck()`,
    4640:          `SNESMonitorSet()`
    4641: @*/
    4642: PetscErrorCode SNESSetUpdate(SNES snes, SNESUpdateFn *func)
    4643: {
    4644:   PetscFunctionBegin;
    4646:   snes->ops->update = func;
    4647:   PetscFunctionReturn(PETSC_SUCCESS);
    4648: }

    4650: /*@
    4651:   SNESConvergedReasonView - Displays the reason a `SNES` solve converged or diverged to a viewer

    4653:   Collective

    4655:   Input Parameters:
    4656: + snes   - iterative context obtained from `SNESCreate()`
    4657: - viewer - the viewer to display the reason

    4659:   Options Database Keys:
    4660: + -snes_converged_reason          - print reason for converged or diverged, also prints number of iterations
    4661: - -snes_converged_reason ::failed - only print reason and number of iterations when diverged

    4663:   Level: beginner

    4665:   Note:
    4666:   To change the format of the output call `PetscViewerPushFormat`(viewer,format) before this call. Use `PETSC_VIEWER_DEFAULT` for the default,
    4667:   use `PETSC_VIEWER_FAILED` to only display a reason if it fails.

    4669: .seealso: [](ch_snes), `SNESConvergedReason`, `PetscViewer`, `SNES`,
    4670:           `SNESCreate()`, `SNESSetUp()`, `SNESDestroy()`, `SNESSetTolerances()`, `SNESConvergedDefault()`, `SNESGetConvergedReason()`,
    4671:           `SNESConvergedReasonViewFromOptions()`,
    4672:           `PetscViewerPushFormat()`, `PetscViewerPopFormat()`
    4673: @*/
    4674: PetscErrorCode SNESConvergedReasonView(SNES snes, PetscViewer viewer)
    4675: {
    4676:   PetscViewerFormat format;
    4677:   PetscBool         isAscii;

    4679:   PetscFunctionBegin;
    4680:   if (!viewer) viewer = PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)snes));
    4681:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &isAscii));
    4682:   if (isAscii) {
    4683:     PetscCall(PetscViewerGetFormat(viewer, &format));
    4684:     PetscCall(PetscViewerASCIIAddTab(viewer, ((PetscObject)snes)->tablevel + 1));
    4685:     if (format == PETSC_VIEWER_ASCII_INFO_DETAIL) {
    4686:       DM       dm;
    4687:       Vec      u;
    4688:       PetscDS  prob;
    4689:       PetscInt Nf, f;
    4690:       PetscErrorCode (**exactSol)(PetscInt, PetscReal, const PetscReal[], PetscInt, PetscScalar[], void *);
    4691:       void    **exactCtx;
    4692:       PetscReal error;

    4694:       PetscCall(SNESGetDM(snes, &dm));
    4695:       PetscCall(SNESGetSolution(snes, &u));
    4696:       PetscCall(DMGetDS(dm, &prob));
    4697:       PetscCall(PetscDSGetNumFields(prob, &Nf));
    4698:       PetscCall(PetscMalloc2(Nf, &exactSol, Nf, &exactCtx));
    4699:       for (f = 0; f < Nf; ++f) PetscCall(PetscDSGetExactSolution(prob, f, &exactSol[f], &exactCtx[f]));
    4700:       PetscCall(DMComputeL2Diff(dm, 0.0, exactSol, exactCtx, u, &error));
    4701:       PetscCall(PetscFree2(exactSol, exactCtx));
    4702:       if (error < 1.0e-11) PetscCall(PetscViewerASCIIPrintf(viewer, "L_2 Error: < 1.0e-11\n"));
    4703:       else PetscCall(PetscViewerASCIIPrintf(viewer, "L_2 Error: %g\n", (double)error));
    4704:     }
    4705:     if (snes->reason > 0 && format != PETSC_VIEWER_FAILED) {
    4706:       if (((PetscObject)snes)->prefix) {
    4707:         PetscCall(PetscViewerASCIIPrintf(viewer, "Nonlinear %s solve converged due to %s iterations %" PetscInt_FMT "\n", ((PetscObject)snes)->prefix, SNESConvergedReasons[snes->reason], snes->iter));
    4708:       } else {
    4709:         PetscCall(PetscViewerASCIIPrintf(viewer, "Nonlinear solve converged due to %s iterations %" PetscInt_FMT "\n", SNESConvergedReasons[snes->reason], snes->iter));
    4710:       }
    4711:     } else if (snes->reason <= 0) {
    4712:       if (((PetscObject)snes)->prefix) {
    4713:         PetscCall(PetscViewerASCIIPrintf(viewer, "Nonlinear %s solve did not converge due to %s iterations %" PetscInt_FMT "\n", ((PetscObject)snes)->prefix, SNESConvergedReasons[snes->reason], snes->iter));
    4714:       } else {
    4715:         PetscCall(PetscViewerASCIIPrintf(viewer, "Nonlinear solve did not converge due to %s iterations %" PetscInt_FMT "\n", SNESConvergedReasons[snes->reason], snes->iter));
    4716:       }
    4717:     }
    4718:     PetscCall(PetscViewerASCIISubtractTab(viewer, ((PetscObject)snes)->tablevel + 1));
    4719:   }
    4720:   PetscFunctionReturn(PETSC_SUCCESS);
    4721: }

    4723: /*@C
    4724:   SNESConvergedReasonViewSet - Sets an ADDITIONAL function that is to be used at the
    4725:   end of the nonlinear solver to display the convergence reason of the nonlinear solver.

    4727:   Logically Collective

    4729:   Input Parameters:
    4730: + snes              - the `SNES` context
    4731: . f                 - the `SNESConvergedReason` view function
    4732: . vctx              - [optional] user-defined context for private data for the `SNESConvergedReason` view function (use `NULL` if no context is desired)
    4733: - reasonviewdestroy - [optional] routine that frees the context (may be `NULL`), see `PetscCtxDestroyFn` for the calling sequence

    4735:   Calling sequence of `f`:
    4736: + snes - the `SNES` context
    4737: - vctx - [optional] context for private data for the function

    4739:   Options Database Keys:
    4740: + -snes_converged_reason             - sets a default `SNESConvergedReasonView()`
    4741: - -snes_converged_reason_view_cancel - cancels all converged reason viewers that have been hardwired into a code by
    4742:                                        calls to `SNESConvergedReasonViewSet()`, but does not cancel those set via the options database.

    4744:   Level: intermediate

    4746:   Note:
    4747:   Several different converged reason view routines may be set by calling
    4748:   `SNESConvergedReasonViewSet()` multiple times; all will be called in the
    4749:   order in which they were set.

    4751: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESConvergedReason`, `SNESGetConvergedReason()`, `SNESConvergedReasonView()`, `SNESConvergedReasonViewCancel()`,
    4752:           `PetscCtxDestroyFn`
    4753: @*/
    4754: PetscErrorCode SNESConvergedReasonViewSet(SNES snes, PetscErrorCode (*f)(SNES snes, PetscCtx vctx), PetscCtx vctx, PetscCtxDestroyFn *reasonviewdestroy)
    4755: {
    4756:   PetscFunctionBegin;
    4758:   for (PetscInt i = 0; i < snes->numberreasonviews; i++) {
    4759:     PetscBool identical;

    4761:     PetscCall(PetscMonitorCompare((PetscErrorCode (*)(void))(PetscVoidFn *)f, vctx, reasonviewdestroy, (PetscErrorCode (*)(void))(PetscVoidFn *)snes->reasonview[i], snes->reasonviewcontext[i], snes->reasonviewdestroy[i], &identical));
    4762:     if (identical) PetscFunctionReturn(PETSC_SUCCESS);
    4763:   }
    4764:   PetscCheck(snes->numberreasonviews < MAXSNESREASONVIEWS, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Too many SNES reasonview set");
    4765:   snes->reasonview[snes->numberreasonviews]          = f;
    4766:   snes->reasonviewdestroy[snes->numberreasonviews]   = reasonviewdestroy;
    4767:   snes->reasonviewcontext[snes->numberreasonviews++] = vctx;
    4768:   PetscFunctionReturn(PETSC_SUCCESS);
    4769: }

    4771: /*@
    4772:   SNESConvergedReasonViewFromOptions - Processes command line options to determine if/how a `SNESConvergedReason` is to be viewed at the end of `SNESSolve()`
    4773:   All the user-provided viewer routines set with `SNESConvergedReasonViewSet()` will be called, if they exist.

    4775:   Collective

    4777:   Input Parameter:
    4778: . snes - the `SNES` object

    4780:   Level: advanced

    4782:   Note:
    4783:   This function has a different API and behavior than `PetscObjectViewFromOptions()`

    4785: .seealso: [](ch_snes), `SNES`, `SNESConvergedReason`, `SNESConvergedReasonViewSet()`, `SNESCreate()`, `SNESSetUp()`, `SNESDestroy()`,
    4786:           `SNESSetTolerances()`, `SNESConvergedDefault()`, `SNESGetConvergedReason()`, `SNESConvergedReasonView()`
    4787: @*/
    4788: PetscErrorCode SNESConvergedReasonViewFromOptions(SNES snes)
    4789: {
    4790:   static PetscBool incall = PETSC_FALSE;

    4792:   PetscFunctionBegin;
    4793:   if (incall) PetscFunctionReturn(PETSC_SUCCESS);
    4794:   incall = PETSC_TRUE;

    4796:   /* All user-provided viewers are called first, if they exist. */
    4797:   for (PetscInt i = 0; i < snes->numberreasonviews; i++) PetscCall((*snes->reasonview[i])(snes, snes->reasonviewcontext[i]));

    4799:   /* Call PETSc default routine if users ask for it */
    4800:   if (snes->convergedreasonviewer) {
    4801:     PetscCall(PetscViewerPushFormat(snes->convergedreasonviewer, snes->convergedreasonformat));
    4802:     PetscCall(SNESConvergedReasonView(snes, snes->convergedreasonviewer));
    4803:     PetscCall(PetscViewerPopFormat(snes->convergedreasonviewer));
    4804:   }
    4805:   incall = PETSC_FALSE;
    4806:   PetscFunctionReturn(PETSC_SUCCESS);
    4807: }

    4809: /*@
    4810:   SNESSolve - Solves a nonlinear system $F(x) = b $ associated with a `SNES` object

    4812:   Collective

    4814:   Input Parameters:
    4815: + snes - the `SNES` context
    4816: . b    - the constant part of the equation $F(x) = b$, or `NULL` to use zero.
    4817: - x    - the solution vector.

    4819:   Level: beginner

    4821:   Note:
    4822:   The user should initialize the vector, `x`, with the initial guess
    4823:   for the nonlinear solve prior to calling `SNESSolve()` .

    4825: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESDestroy()`, `SNESSetFunction()`, `SNESSetJacobian()`, `SNESSetGridSequence()`, `SNESGetSolution()`,
    4826:           `SNESNewtonTRSetPreCheck()`, `SNESNewtonTRGetPreCheck()`, `SNESNewtonTRSetPostCheck()`, `SNESNewtonTRGetPostCheck()`,
    4827:           `SNESLineSearchSetPostCheck()`, `SNESLineSearchGetPostCheck()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchGetPreCheck()`
    4828: @*/
    4829: PetscErrorCode SNESSolve(SNES snes, Vec b, Vec x)
    4830: {
    4831:   PetscBool flg;
    4832:   PetscInt  grid;
    4833:   Vec       xcreated = NULL;
    4834:   DM        dm;

    4836:   PetscFunctionBegin;
    4839:   if (x) PetscCheckSameComm(snes, 1, x, 3);
    4841:   if (b) PetscCheckSameComm(snes, 1, b, 2);

    4843:   /* High level operations using the nonlinear solver */
    4844:   {
    4845:     PetscViewer       viewer;
    4846:     PetscViewerFormat format;
    4847:     PetscInt          num;
    4848:     PetscBool         flg;
    4849:     static PetscBool  incall = PETSC_FALSE;

    4851:     if (!incall) {
    4852:       /* Estimate the convergence rate of the discretization */
    4853:       PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_convergence_estimate", &viewer, &format, &flg));
    4854:       if (flg) {
    4855:         PetscConvEst conv;
    4856:         DM           dm;
    4857:         PetscReal   *alpha; /* Convergence rate of the solution error for each field in the L_2 norm */
    4858:         PetscInt     Nf;

    4860:         incall = PETSC_TRUE;
    4861:         PetscCall(SNESGetDM(snes, &dm));
    4862:         PetscCall(DMGetNumFields(dm, &Nf));
    4863:         PetscCall(PetscCalloc1(Nf, &alpha));
    4864:         PetscCall(PetscConvEstCreate(PetscObjectComm((PetscObject)snes), &conv));
    4865:         PetscCall(PetscConvEstSetSolver(conv, (PetscObject)snes));
    4866:         PetscCall(PetscConvEstSetFromOptions(conv));
    4867:         PetscCall(PetscConvEstSetUp(conv));
    4868:         PetscCall(PetscConvEstGetConvRate(conv, alpha));
    4869:         PetscCall(PetscViewerPushFormat(viewer, format));
    4870:         PetscCall(PetscConvEstRateView(conv, alpha, viewer));
    4871:         PetscCall(PetscViewerPopFormat(viewer));
    4872:         PetscCall(PetscViewerDestroy(&viewer));
    4873:         PetscCall(PetscConvEstDestroy(&conv));
    4874:         PetscCall(PetscFree(alpha));
    4875:         incall = PETSC_FALSE;
    4876:       }
    4877:       /* Adaptively refine the initial grid */
    4878:       num = 1;
    4879:       PetscCall(PetscOptionsGetInt(NULL, ((PetscObject)snes)->prefix, "-snes_adapt_initial", &num, &flg));
    4880:       if (flg) {
    4881:         DMAdaptor adaptor;

    4883:         incall = PETSC_TRUE;
    4884:         PetscCall(DMAdaptorCreate(PetscObjectComm((PetscObject)snes), &adaptor));
    4885:         PetscCall(DMAdaptorSetSolver(adaptor, snes));
    4886:         PetscCall(DMAdaptorSetSequenceLength(adaptor, num));
    4887:         PetscCall(DMAdaptorSetFromOptions(adaptor));
    4888:         PetscCall(DMAdaptorSetUp(adaptor));
    4889:         PetscCall(DMAdaptorAdapt(adaptor, x, DM_ADAPTATION_INITIAL, &dm, &x));
    4890:         PetscCall(DMAdaptorDestroy(&adaptor));
    4891:         incall = PETSC_FALSE;
    4892:       }
    4893:       /* Use grid sequencing to adapt */
    4894:       num = 0;
    4895:       PetscCall(PetscOptionsGetInt(NULL, ((PetscObject)snes)->prefix, "-snes_adapt_sequence", &num, NULL));
    4896:       if (num) {
    4897:         DMAdaptor   adaptor;
    4898:         const char *prefix;

    4900:         incall = PETSC_TRUE;
    4901:         PetscCall(DMAdaptorCreate(PetscObjectComm((PetscObject)snes), &adaptor));
    4902:         PetscCall(SNESGetOptionsPrefix(snes, &prefix));
    4903:         PetscCall(DMAdaptorSetOptionsPrefix(adaptor, prefix));
    4904:         PetscCall(DMAdaptorSetSolver(adaptor, snes));
    4905:         PetscCall(DMAdaptorSetSequenceLength(adaptor, num));
    4906:         PetscCall(DMAdaptorSetFromOptions(adaptor));
    4907:         PetscCall(DMAdaptorSetUp(adaptor));
    4908:         PetscCall(PetscObjectViewFromOptions((PetscObject)adaptor, NULL, "-snes_adapt_view"));
    4909:         PetscCall(DMAdaptorAdapt(adaptor, x, DM_ADAPTATION_SEQUENTIAL, &dm, &x));
    4910:         PetscCall(DMAdaptorDestroy(&adaptor));
    4911:         incall = PETSC_FALSE;
    4912:       }
    4913:     }
    4914:   }
    4915:   if (!x) x = snes->vec_sol;
    4916:   if (!x) {
    4917:     PetscCall(SNESGetDM(snes, &dm));
    4918:     PetscCall(DMCreateGlobalVector(dm, &xcreated));
    4919:     x = xcreated;
    4920:   }
    4921:   PetscCall(SNESViewFromOptions(snes, NULL, "-snes_view_pre"));

    4923:   for (grid = 0; grid < snes->gridsequence; grid++) PetscCall(PetscViewerASCIIPushTab(PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)snes))));
    4924:   for (grid = 0; grid < snes->gridsequence + 1; grid++) {
    4925:     /* set solution vector */
    4926:     if (!grid) PetscCall(PetscObjectReference((PetscObject)x));
    4927:     PetscCall(VecDestroy(&snes->vec_sol));
    4928:     snes->vec_sol = x;
    4929:     PetscCall(SNESGetDM(snes, &dm));

    4931:     /* set affine vector if provided */
    4932:     PetscCall(PetscObjectReference((PetscObject)b));
    4933:     PetscCall(VecDestroy(&snes->vec_rhs));
    4934:     snes->vec_rhs = b;

    4936:     if (snes->vec_rhs) PetscCheck(snes->vec_func != snes->vec_rhs, PETSC_COMM_SELF, PETSC_ERR_ARG_IDN, "Right hand side vector cannot be function vector");
    4937:     PetscCheck(snes->vec_func != snes->vec_sol, PETSC_COMM_SELF, PETSC_ERR_ARG_IDN, "Solution vector cannot be function vector");
    4938:     PetscCheck(snes->vec_rhs != snes->vec_sol, PETSC_COMM_SELF, PETSC_ERR_ARG_IDN, "Solution vector cannot be right-hand side vector");
    4939:     if (!snes->vec_sol_update /* && snes->vec_sol */) PetscCall(VecDuplicate(snes->vec_sol, &snes->vec_sol_update));
    4940:     PetscCall(DMShellSetGlobalVector(dm, snes->vec_sol));
    4941:     PetscCall(SNESSetUp(snes));

    4943:     if (!grid) {
    4944:       if (snes->ops->computeinitialguess) PetscCallBack("SNES callback compute initial guess", (*snes->ops->computeinitialguess)(snes, snes->vec_sol, snes->initialguessP));
    4945:     }

    4947:     if (snes->conv_hist_reset) snes->conv_hist_len = 0;
    4948:     PetscCall(SNESResetCounters(snes));
    4949:     snes->reason = SNES_CONVERGED_ITERATING;
    4950:     PetscCall(PetscLogEventBegin(SNES_Solve, snes, 0, 0, 0));
    4951:     PetscUseTypeMethod(snes, solve);
    4952:     PetscCall(PetscLogEventEnd(SNES_Solve, snes, 0, 0, 0));
    4953:     PetscCheck(snes->reason, PETSC_COMM_SELF, PETSC_ERR_PLIB, "Internal error, solver %s returned without setting converged reason", ((PetscObject)snes)->type_name);
    4954:     snes->functiondomainerror  = PETSC_FALSE; /* clear the flag if it has been set */
    4955:     snes->objectivedomainerror = PETSC_FALSE; /* clear the flag if it has been set */
    4956:     snes->jacobiandomainerror  = PETSC_FALSE; /* clear the flag if it has been set */

    4958:     if (snes->lagjac_persist) snes->jac_iter += snes->iter;
    4959:     if (snes->lagpre_persist) snes->pre_iter += snes->iter;

    4961:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_test_local_min", NULL, NULL, &flg));
    4962:     if (flg && !PetscPreLoadingOn) PetscCall(SNESTestLocalMin(snes));
    4963:     /* Call converged reason views. This may involve user-provided viewers as well */
    4964:     PetscCall(SNESConvergedReasonViewFromOptions(snes));

    4966:     if (snes->errorifnotconverged) {
    4967:       if (snes->reason < 0) PetscCall(SNESMonitorCancel(snes));
    4968:       PetscCheck(snes->reason >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_NOT_CONVERGED, "SNESSolve has not converged");
    4969:     }
    4970:     if (snes->reason < 0) break;
    4971:     if (grid < snes->gridsequence) {
    4972:       DM  fine;
    4973:       Vec xnew;
    4974:       Mat interp;

    4976:       PetscCall(DMRefine(snes->dm, PetscObjectComm((PetscObject)snes), &fine));
    4977:       PetscCheck(fine, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_INCOMP, "DMRefine() did not perform any refinement, cannot continue grid sequencing");
    4978:       PetscCall(DMGetCoordinatesLocalSetUp(fine));
    4979:       PetscCall(DMCreateInterpolation(snes->dm, fine, &interp, NULL));
    4980:       PetscCall(DMCreateGlobalVector(fine, &xnew));
    4981:       PetscCall(MatInterpolate(interp, x, xnew));
    4982:       PetscCall(DMInterpolate(snes->dm, interp, fine));
    4983:       PetscCall(MatDestroy(&interp));
    4984:       x = xnew;

    4986:       PetscCall(SNESReset(snes));
    4987:       PetscCall(SNESSetDM(snes, fine));
    4988:       PetscCall(SNESResetFromOptions(snes));
    4989:       PetscCall(DMDestroy(&fine));
    4990:       PetscCall(PetscViewerASCIIPopTab(PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)snes))));
    4991:     }
    4992:   }
    4993:   PetscCall(SNESViewFromOptions(snes, NULL, "-snes_view"));
    4994:   PetscCall(VecViewFromOptions(snes->vec_sol, (PetscObject)snes, "-snes_view_solution"));
    4995:   PetscCall(DMMonitor(snes->dm));
    4996:   PetscCall(SNESMonitorPauseFinal_Internal(snes));

    4998:   PetscCall(VecDestroy(&xcreated));
    4999:   PetscCall(PetscObjectSAWsBlock((PetscObject)snes));
    5000:   PetscFunctionReturn(PETSC_SUCCESS);
    5001: }

    5003: /* --------- Internal routines for SNES Package --------- */

    5005: /*@
    5006:   SNESSetType - Sets the algorithm/method to be used to solve the nonlinear system with the given `SNES`

    5008:   Collective

    5010:   Input Parameters:
    5011: + snes - the `SNES` context
    5012: - type - a known method

    5014:   Options Database Key:
    5015: . -snes_type type - Sets the method; see `SNESType`

    5017:   Level: intermediate

    5019:   Notes:
    5020:   See `SNESType` for available methods (for instance)
    5021: +    `SNESNEWTONLS` - Newton's method with line search
    5022:   (systems of nonlinear equations)
    5023: -    `SNESNEWTONTR` - Newton's method with trust region
    5024:   (systems of nonlinear equations)

    5026:   Normally, it is best to use the `SNESSetFromOptions()` command and then
    5027:   set the `SNES` solver type from the options database rather than by using
    5028:   this routine.  Using the options database provides the user with
    5029:   maximum flexibility in evaluating the many nonlinear solvers.
    5030:   The `SNESSetType()` routine is provided for those situations where it
    5031:   is necessary to set the nonlinear solver independently of the command
    5032:   line or options database.  This might be the case, for example, when
    5033:   the choice of solver changes during the execution of the program,
    5034:   and the user's application is taking responsibility for choosing the
    5035:   appropriate method.

    5037:   Developer Note:
    5038:   `SNESRegister()` adds a constructor for a new `SNESType` to `SNESList`, `SNESSetType()` locates
    5039:   the constructor in that list and calls it to create the specific object.

    5041: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESType`, `SNESCreate()`, `SNESDestroy()`, `SNESGetType()`, `SNESSetFromOptions()`
    5042: @*/
    5043: PetscErrorCode SNESSetType(SNES snes, SNESType type)
    5044: {
    5045:   PetscBool match;
    5046:   PetscErrorCode (*r)(SNES);

    5048:   PetscFunctionBegin;
    5050:   PetscAssertPointer(type, 2);

    5052:   PetscCall(PetscObjectTypeCompare((PetscObject)snes, type, &match));
    5053:   if (match) PetscFunctionReturn(PETSC_SUCCESS);

    5055:   PetscCall(PetscFunctionListFind(SNESList, type, &r));
    5056:   PetscCheck(r, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_UNKNOWN_TYPE, "Unable to find requested SNES type %s", type);
    5057:   /* Destroy the previous private SNES context */
    5058:   PetscTryTypeMethod(snes, destroy);
    5059:   /* Reinitialize type-specific function pointers in SNESOps structure */
    5060:   snes->ops->reset          = NULL;
    5061:   snes->ops->setup          = NULL;
    5062:   snes->ops->solve          = NULL;
    5063:   snes->ops->view           = NULL;
    5064:   snes->ops->setfromoptions = NULL;
    5065:   snes->ops->destroy        = NULL;

    5067:   /* It may happen the user has customized the line search before calling SNESSetType */
    5068:   if (((PetscObject)snes)->type_name) PetscCall(SNESLineSearchDestroy(&snes->linesearch));

    5070:   /* Call the SNESCreate_XXX routine for this particular Nonlinear solver */
    5071:   snes->setupcalled = PETSC_FALSE;

    5073:   PetscCall(PetscObjectChangeTypeName((PetscObject)snes, type));
    5074:   PetscCall((*r)(snes));
    5075:   PetscFunctionReturn(PETSC_SUCCESS);
    5076: }

    5078: /*@
    5079:   SNESGetType - Gets the `SNES` method type and name (as a string).

    5081:   Not Collective

    5083:   Input Parameter:
    5084: . snes - nonlinear solver context

    5086:   Output Parameter:
    5087: . type - `SNES` method (a character string)

    5089:   Level: intermediate

    5091:   Note:
    5092:   `type` should not be retained for later use as it will be an invalid pointer if the `SNESType` of `snes` is changed.

    5094: .seealso: [](ch_snes), `SNESSetType()`, `SNESType`, `SNESSetFromOptions()`, `SNES`, `PetscObjectTypeCompare()`, `PetscObjectTypeCompareAny()`
    5095: @*/
    5096: PetscErrorCode SNESGetType(SNES snes, SNESType *type)
    5097: {
    5098:   PetscFunctionBegin;
    5100:   PetscAssertPointer(type, 2);
    5101:   *type = ((PetscObject)snes)->type_name;
    5102:   PetscFunctionReturn(PETSC_SUCCESS);
    5103: }

    5105: /*@
    5106:   SNESSetSolution - Sets the solution vector for use by the `SNES` routines.

    5108:   Logically Collective

    5110:   Input Parameters:
    5111: + snes - the `SNES` context obtained from `SNESCreate()`
    5112: - u    - the solution vector

    5114:   Level: beginner

    5116: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESGetSolution()`, `Vec`
    5117: @*/
    5118: PetscErrorCode SNESSetSolution(SNES snes, Vec u)
    5119: {
    5120:   DM dm;

    5122:   PetscFunctionBegin;
    5125:   PetscCall(PetscObjectReference((PetscObject)u));
    5126:   PetscCall(VecDestroy(&snes->vec_sol));

    5128:   snes->vec_sol = u;

    5130:   PetscCall(SNESGetDM(snes, &dm));
    5131:   PetscCall(DMShellSetGlobalVector(dm, u));
    5132:   PetscFunctionReturn(PETSC_SUCCESS);
    5133: }

    5135: /*@
    5136:   SNESGetSolution - Returns the vector where the approximate solution is
    5137:   stored. This is the fine grid solution when using `SNESSetGridSequence()`.

    5139:   Not Collective, but `x` is parallel if `snes` is parallel

    5141:   Input Parameter:
    5142: . snes - the `SNES` context

    5144:   Output Parameter:
    5145: . x - the solution

    5147:   Level: intermediate

    5149: .seealso: [](ch_snes), `SNESSetSolution()`, `SNESSolve()`, `SNES`, `SNESGetSolutionUpdate()`, `SNESGetFunction()`
    5150: @*/
    5151: PetscErrorCode SNESGetSolution(SNES snes, Vec *x)
    5152: {
    5153:   PetscFunctionBegin;
    5155:   PetscAssertPointer(x, 2);
    5156:   *x = snes->vec_sol;
    5157:   PetscFunctionReturn(PETSC_SUCCESS);
    5158: }

    5160: /*@
    5161:   SNESGetSolutionUpdate - Returns the vector where the solution update is
    5162:   stored.

    5164:   Not Collective, but `x` is parallel if `snes` is parallel

    5166:   Input Parameter:
    5167: . snes - the `SNES` context

    5169:   Output Parameter:
    5170: . x - the solution update

    5172:   Level: advanced

    5174: .seealso: [](ch_snes), `SNES`, `SNESGetSolution()`, `SNESGetFunction()`
    5175: @*/
    5176: PetscErrorCode SNESGetSolutionUpdate(SNES snes, Vec *x)
    5177: {
    5178:   PetscFunctionBegin;
    5180:   PetscAssertPointer(x, 2);
    5181:   *x = snes->vec_sol_update;
    5182:   PetscFunctionReturn(PETSC_SUCCESS);
    5183: }

    5185: /*@C
    5186:   SNESGetFunction - Returns the function that defines the nonlinear system set with `SNESSetFunction()`

    5188:   Not Collective, but `r` is parallel if `snes` is parallel. Collective if `r` is requested, but has not been created yet.

    5190:   Input Parameter:
    5191: . snes - the `SNES` context

    5193:   Output Parameters:
    5194: + r   - the vector that is used to store residuals (or `NULL` if you don't want it)
    5195: . f   - the function (or `NULL` if you don't want it);  for calling sequence see `SNESFunctionFn`
    5196: - ctx - the function context (or `NULL` if you don't want it)

    5198:   Level: advanced

    5200:   Note:
    5201:   The vector `r` DOES NOT, in general, contain the current value of the `SNES` nonlinear function

    5203: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetFunction()`, `SNESGetSolution()`, `SNESFunctionFn`
    5204: @*/
    5205: PetscErrorCode SNESGetFunction(SNES snes, Vec *r, SNESFunctionFn **f, PetscCtxRt ctx)
    5206: {
    5207:   DM dm;

    5209:   PetscFunctionBegin;
    5211:   if (r) {
    5212:     if (!snes->vec_func) {
    5213:       if (snes->vec_rhs) {
    5214:         PetscCall(VecDuplicate(snes->vec_rhs, &snes->vec_func));
    5215:       } else if (snes->vec_sol) {
    5216:         PetscCall(VecDuplicate(snes->vec_sol, &snes->vec_func));
    5217:       } else if (snes->dm) {
    5218:         PetscCall(DMCreateGlobalVector(snes->dm, &snes->vec_func));
    5219:       }
    5220:     }
    5221:     *r = snes->vec_func;
    5222:   }
    5223:   PetscCall(SNESGetDM(snes, &dm));
    5224:   PetscCall(DMSNESGetFunction(dm, f, ctx));
    5225:   PetscFunctionReturn(PETSC_SUCCESS);
    5226: }

    5228: /*@C
    5229:   SNESGetNGS - Returns the function and context set with `SNESSetNGS()`

    5231:   Input Parameter:
    5232: . snes - the `SNES` context

    5234:   Output Parameters:
    5235: + f   - the function (or `NULL`) see `SNESNGSFn` for calling sequence
    5236: - ctx - the function context (or `NULL`)

    5238:   Level: advanced

    5240: .seealso: [](ch_snes), `SNESSetNGS()`, `SNESGetFunction()`, `SNESNGSFn`
    5241: @*/
    5242: PetscErrorCode SNESGetNGS(SNES snes, SNESNGSFn **f, PetscCtxRt ctx)
    5243: {
    5244:   DM dm;

    5246:   PetscFunctionBegin;
    5248:   PetscCall(SNESGetDM(snes, &dm));
    5249:   PetscCall(DMSNESGetNGS(dm, f, ctx));
    5250:   PetscFunctionReturn(PETSC_SUCCESS);
    5251: }

    5253: /*@
    5254:   SNESSetOptionsPrefix - Sets the prefix used for searching for all
    5255:   `SNES` options in the database.

    5257:   Logically Collective

    5259:   Input Parameters:
    5260: + snes   - the `SNES` context
    5261: - prefix - the prefix to prepend to all option names

    5263:   Level: advanced

    5265:   Note:
    5266:   A hyphen (-) must NOT be given at the beginning of the prefix name.
    5267:   The first character of all runtime options is AUTOMATICALLY the hyphen.

    5269: .seealso: [](ch_snes), `SNES`, `SNESSetFromOptions()`, `SNESAppendOptionsPrefix()`
    5270: @*/
    5271: PetscErrorCode SNESSetOptionsPrefix(SNES snes, const char prefix[])
    5272: {
    5273:   PetscFunctionBegin;
    5275:   PetscCall(PetscObjectSetOptionsPrefix((PetscObject)snes, prefix));
    5276:   if (!snes->ksp) PetscCall(SNESGetKSP(snes, &snes->ksp));
    5277:   if (snes->linesearch) {
    5278:     PetscCall(SNESGetLineSearch(snes, &snes->linesearch));
    5279:     PetscCall(PetscObjectSetOptionsPrefix((PetscObject)snes->linesearch, prefix));
    5280:   }
    5281:   PetscCall(KSPSetOptionsPrefix(snes->ksp, prefix));
    5282:   PetscFunctionReturn(PETSC_SUCCESS);
    5283: }

    5285: /*@
    5286:   SNESAppendOptionsPrefix - Appends to the prefix used for searching for all
    5287:   `SNES` options in the database.

    5289:   Logically Collective

    5291:   Input Parameters:
    5292: + snes   - the `SNES` context
    5293: - prefix - the prefix to prepend to all option names

    5295:   Level: advanced

    5297:   Note:
    5298:   A hyphen (-) must NOT be given at the beginning of the prefix name.
    5299:   The first character of all runtime options is AUTOMATICALLY the hyphen.

    5301: .seealso: [](ch_snes), `SNESGetOptionsPrefix()`, `SNESSetOptionsPrefix()`
    5302: @*/
    5303: PetscErrorCode SNESAppendOptionsPrefix(SNES snes, const char prefix[])
    5304: {
    5305:   PetscFunctionBegin;
    5307:   PetscCall(PetscObjectAppendOptionsPrefix((PetscObject)snes, prefix));
    5308:   if (!snes->ksp) PetscCall(SNESGetKSP(snes, &snes->ksp));
    5309:   if (snes->linesearch) {
    5310:     PetscCall(SNESGetLineSearch(snes, &snes->linesearch));
    5311:     PetscCall(PetscObjectAppendOptionsPrefix((PetscObject)snes->linesearch, prefix));
    5312:   }
    5313:   PetscCall(KSPAppendOptionsPrefix(snes->ksp, prefix));
    5314:   PetscFunctionReturn(PETSC_SUCCESS);
    5315: }

    5317: /*@
    5318:   SNESGetOptionsPrefix - Gets the prefix used for searching for all
    5319:   `SNES` options in the database.

    5321:   Not Collective

    5323:   Input Parameter:
    5324: . snes - the `SNES` context

    5326:   Output Parameter:
    5327: . prefix - pointer to the prefix string used

    5329:   Level: advanced

    5331: .seealso: [](ch_snes), `SNES`, `SNESSetOptionsPrefix()`, `SNESAppendOptionsPrefix()`
    5332: @*/
    5333: PetscErrorCode SNESGetOptionsPrefix(SNES snes, const char *prefix[])
    5334: {
    5335:   PetscFunctionBegin;
    5337:   PetscCall(PetscObjectGetOptionsPrefix((PetscObject)snes, prefix));
    5338:   PetscFunctionReturn(PETSC_SUCCESS);
    5339: }

    5341: /*@C
    5342:   SNESRegister - Adds a method to the nonlinear solver package.

    5344:   Not Collective

    5346:   Input Parameters:
    5347: + sname    - name of a new user-defined solver
    5348: - function - routine to create method context

    5350:   Level: advanced

    5352:   Note:
    5353:   `SNESRegister()` may be called multiple times to add several user-defined solvers.

    5355:   Example Usage:
    5356: .vb
    5357:    SNESRegister("my_solver", MySolverCreate);
    5358: .ve

    5360:   Then, your solver can be chosen with the procedural interface via
    5361: .vb
    5362:   SNESSetType(snes, "my_solver")
    5363: .ve
    5364:   or at runtime via the option
    5365: .vb
    5366:   -snes_type my_solver
    5367: .ve

    5369: .seealso: [](ch_snes), `SNESRegisterAll()`, `SNESRegisterDestroy()`
    5370: @*/
    5371: PetscErrorCode SNESRegister(const char sname[], PetscErrorCode (*function)(SNES))
    5372: {
    5373:   PetscFunctionBegin;
    5374:   PetscCall(SNESInitializePackage());
    5375:   PetscCall(PetscFunctionListAdd(&SNESList, sname, function));
    5376:   PetscFunctionReturn(PETSC_SUCCESS);
    5377: }

    5379: /*@
    5380:   SNESTestLocalMin - Diagnostic that probes each entry of the current `SNES` solution to check whether the residual norm has a local minimum along the coordinate directions

    5382:   Collective

    5384:   Input Parameter:
    5385: . snes - the `SNES` context

    5387:   Level: developer

    5389:   Note:
    5390:   Currently intended for serial runs. For each degree of freedom it perturbs the solution by increasing amounts and prints the resulting `SNESComputeFunction()` residual norms so the user can inspect local behavior.

    5392: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESComputeFunction()`
    5393: @*/
    5394: PetscErrorCode SNESTestLocalMin(SNES snes)
    5395: {
    5396:   PetscInt    N, i, j;
    5397:   Vec         u, uh, fh;
    5398:   PetscScalar value;
    5399:   PetscReal   norm;

    5401:   PetscFunctionBegin;
    5402:   PetscCall(SNESGetSolution(snes, &u));
    5403:   PetscCall(VecDuplicate(u, &uh));
    5404:   PetscCall(VecDuplicate(u, &fh));

    5406:   /* currently only works for sequential */
    5407:   PetscCall(PetscPrintf(PetscObjectComm((PetscObject)snes), "Testing FormFunction() for local min\n"));
    5408:   PetscCall(VecGetSize(u, &N));
    5409:   for (i = 0; i < N; i++) {
    5410:     PetscCall(VecCopy(u, uh));
    5411:     PetscCall(PetscPrintf(PetscObjectComm((PetscObject)snes), "i = %" PetscInt_FMT "\n", i));
    5412:     for (j = -10; j < 11; j++) {
    5413:       value = PetscSign(j) * PetscExpReal(PetscAbs(j) - 10.0);
    5414:       PetscCall(VecSetValue(uh, i, value, ADD_VALUES));
    5415:       PetscCall(SNESComputeFunction(snes, uh, fh));
    5416:       PetscCall(VecNorm(fh, NORM_2, &norm)); /* does not handle use of SNESSetFunctionDomainError() correctly */
    5417:       PetscCall(PetscPrintf(PetscObjectComm((PetscObject)snes), "       j norm %" PetscInt_FMT " %18.16e\n", j, (double)norm));
    5418:       value = -value;
    5419:       PetscCall(VecSetValue(uh, i, value, ADD_VALUES));
    5420:     }
    5421:   }
    5422:   PetscCall(VecDestroy(&uh));
    5423:   PetscCall(VecDestroy(&fh));
    5424:   PetscFunctionReturn(PETSC_SUCCESS);
    5425: }

    5427: /*@
    5428:   SNESGetLineSearch - Returns the line search associated with the `SNES`.

    5430:   Not Collective

    5432:   Input Parameter:
    5433: . snes - iterative context obtained from `SNESCreate()`

    5435:   Output Parameter:
    5436: . linesearch - linesearch context

    5438:   Level: beginner

    5440:   Notes:
    5441:   It creates a default line search instance which can be configured as needed in case it has not been already set with `SNESSetLineSearch()`.

    5443:   You can also use the options database keys `-snes_linesearch_*` to configure the line search. See `SNESLineSearchSetFromOptions()` for the possible options.

    5445: .seealso: [](ch_snes), `SNESLineSearch`, `SNESSetLineSearch()`, `SNESLineSearchCreate()`, `SNESLineSearchSetFromOptions()`
    5446: @*/
    5447: PetscErrorCode SNESGetLineSearch(SNES snes, SNESLineSearch *linesearch)
    5448: {
    5449:   const char *optionsprefix;

    5451:   PetscFunctionBegin;
    5453:   PetscAssertPointer(linesearch, 2);
    5454:   if (!snes->linesearch) {
    5455:     PetscCall(SNESGetOptionsPrefix(snes, &optionsprefix));
    5456:     PetscCall(SNESLineSearchCreate(PetscObjectComm((PetscObject)snes), &snes->linesearch));
    5457:     PetscCall(SNESLineSearchSetSNES(snes->linesearch, snes));
    5458:     PetscCall(SNESLineSearchAppendOptionsPrefix(snes->linesearch, optionsprefix));
    5459:     PetscCall(PetscObjectIncrementTabLevel((PetscObject)snes->linesearch, (PetscObject)snes, 1));
    5460:   }
    5461:   *linesearch = snes->linesearch;
    5462:   PetscFunctionReturn(PETSC_SUCCESS);
    5463: }

    5465: /*@
    5466:   SNESKSPSetUseEW - Sets `SNES` to the use Eisenstat-Walker method for
    5467:   computing relative tolerance for linear solvers within an inexact
    5468:   Newton method.

    5470:   Logically Collective

    5472:   Input Parameters:
    5473: + snes - `SNES` context
    5474: - flag - `PETSC_TRUE` or `PETSC_FALSE`

    5476:   Options Database Keys:
    5477: + -snes_ksp_ew                     - use Eisenstat-Walker method for determining linear system convergence
    5478: . -snes_ksp_ew_version ver         - version of  Eisenstat-Walker method
    5479: . -snes_ksp_ew_rtol0 rtol0         - Sets rtol0
    5480: . -snes_ksp_ew_rtolmax rtolmax     - Sets rtolmax
    5481: . -snes_ksp_ew_gamma gamma         - Sets gamma
    5482: . -snes_ksp_ew_alpha alpha         - Sets alpha
    5483: . -snes_ksp_ew_alpha2 alpha2       - Sets alpha2
    5484: - -snes_ksp_ew_threshold threshold - Sets threshold

    5486:   Level: advanced

    5488:   Note:
    5489:   The default is to use a constant relative tolerance for
    5490:   the inner linear solvers.  Alternatively, one can use the
    5491:   Eisenstat-Walker method {cite}`ew96`, where the relative convergence tolerance
    5492:   is reset at each Newton iteration according progress of the nonlinear
    5493:   solver.

    5495: .seealso: [](ch_snes), `KSP`, `SNES`, `SNESKSPGetUseEW()`, `SNESKSPGetParametersEW()`, `SNESKSPSetParametersEW()`
    5496: @*/
    5497: PetscErrorCode SNESKSPSetUseEW(SNES snes, PetscBool flag)
    5498: {
    5499:   PetscFunctionBegin;
    5502:   snes->ksp_ewconv = flag;
    5503:   PetscFunctionReturn(PETSC_SUCCESS);
    5504: }

    5506: /*@
    5507:   SNESKSPGetUseEW - Gets if `SNES` is using Eisenstat-Walker method
    5508:   for computing relative tolerance for linear solvers within an
    5509:   inexact Newton method.

    5511:   Not Collective

    5513:   Input Parameter:
    5514: . snes - `SNES` context

    5516:   Output Parameter:
    5517: . flag - `PETSC_TRUE` or `PETSC_FALSE`

    5519:   Level: advanced

    5521: .seealso: [](ch_snes), `SNESKSPSetUseEW()`, `SNESKSPGetParametersEW()`, `SNESKSPSetParametersEW()`
    5522: @*/
    5523: PetscErrorCode SNESKSPGetUseEW(SNES snes, PetscBool *flag)
    5524: {
    5525:   PetscFunctionBegin;
    5527:   PetscAssertPointer(flag, 2);
    5528:   *flag = snes->ksp_ewconv;
    5529:   PetscFunctionReturn(PETSC_SUCCESS);
    5530: }

    5532: /*@
    5533:   SNESKSPSetParametersEW - Sets parameters for Eisenstat-Walker
    5534:   convergence criteria for the linear solvers within an inexact
    5535:   Newton method.

    5537:   Logically Collective

    5539:   Input Parameters:
    5540: + snes      - `SNES` context
    5541: . version   - version 1, 2 (default is 2), 3 or 4
    5542: . rtol_0    - initial relative tolerance (0 <= rtol_0 < 1)
    5543: . rtol_max  - maximum relative tolerance (0 <= rtol_max < 1)
    5544: . gamma     - multiplicative factor for version 2 rtol computation
    5545:              (0 <= gamma2 <= 1)
    5546: . alpha     - power for version 2 rtol computation (1 < alpha <= 2)
    5547: . alpha2    - power for safeguard
    5548: - threshold - threshold for imposing safeguard (0 < threshold < 1)

    5550:   Level: advanced

    5552:   Notes:
    5553:   Version 3 was contributed by Luis Chacon, June 2006.

    5555:   Use `PETSC_CURRENT` to retain the default for any of the parameters.

    5557: .seealso: [](ch_snes), `SNES`, `SNESKSPSetUseEW()`, `SNESKSPGetUseEW()`, `SNESKSPGetParametersEW()`
    5558: @*/
    5559: PetscErrorCode SNESKSPSetParametersEW(SNES snes, PetscInt version, PetscReal rtol_0, PetscReal rtol_max, PetscReal gamma, PetscReal alpha, PetscReal alpha2, PetscReal threshold)
    5560: {
    5561:   SNESKSPEW *kctx;

    5563:   PetscFunctionBegin;
    5565:   kctx = (SNESKSPEW *)snes->kspconvctx;
    5566:   PetscCheck(kctx, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "No Eisenstat-Walker context existing");

    5575:   if (version != PETSC_CURRENT) kctx->version = version;
    5576:   if (rtol_0 != (PetscReal)PETSC_CURRENT) kctx->rtol_0 = rtol_0;
    5577:   if (rtol_max != (PetscReal)PETSC_CURRENT) kctx->rtol_max = rtol_max;
    5578:   if (gamma != (PetscReal)PETSC_CURRENT) kctx->gamma = gamma;
    5579:   if (alpha != (PetscReal)PETSC_CURRENT) kctx->alpha = alpha;
    5580:   if (alpha2 != (PetscReal)PETSC_CURRENT) kctx->alpha2 = alpha2;
    5581:   if (threshold != (PetscReal)PETSC_CURRENT) kctx->threshold = threshold;

    5583:   PetscCheck(kctx->version >= 1 && kctx->version <= 4, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Only versions 1 to 4 are supported: %" PetscInt_FMT, kctx->version);
    5584:   PetscCheck(kctx->rtol_0 >= 0.0 && kctx->rtol_0 < 1.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "0.0 <= rtol_0 < 1.0: %g", (double)kctx->rtol_0);
    5585:   PetscCheck(kctx->rtol_max >= 0.0 && kctx->rtol_max < 1.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "0.0 <= rtol_max (%g) < 1.0", (double)kctx->rtol_max);
    5586:   PetscCheck(kctx->gamma >= 0.0 && kctx->gamma <= 1.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "0.0 <= gamma (%g) <= 1.0", (double)kctx->gamma);
    5587:   PetscCheck(kctx->alpha > 1.0 && kctx->alpha <= 2.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "1.0 < alpha (%g) <= 2.0", (double)kctx->alpha);
    5588:   PetscCheck(kctx->threshold > 0.0 && kctx->threshold < 1.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "0.0 < threshold (%g) < 1.0", (double)kctx->threshold);
    5589:   PetscFunctionReturn(PETSC_SUCCESS);
    5590: }

    5592: /*@
    5593:   SNESKSPGetParametersEW - Gets parameters for Eisenstat-Walker
    5594:   convergence criteria for the linear solvers within an inexact
    5595:   Newton method.

    5597:   Not Collective

    5599:   Input Parameter:
    5600: . snes - `SNES` context

    5602:   Output Parameters:
    5603: + version   - version 1, 2 (default is 2), 3 or 4
    5604: . rtol_0    - initial relative tolerance (0 <= rtol_0 < 1)
    5605: . rtol_max  - maximum relative tolerance (0 <= rtol_max < 1)
    5606: . gamma     - multiplicative factor for version 2 rtol computation (0 <= gamma2 <= 1)
    5607: . alpha     - power for version 2 rtol computation (1 < alpha <= 2)
    5608: . alpha2    - power for safeguard
    5609: - threshold - threshold for imposing safeguard (0 < threshold < 1)

    5611:   Level: advanced

    5613: .seealso: [](ch_snes), `SNES`, `SNESKSPSetUseEW()`, `SNESKSPGetUseEW()`, `SNESKSPSetParametersEW()`
    5614: @*/
    5615: PetscErrorCode SNESKSPGetParametersEW(SNES snes, PetscInt *version, PetscReal *rtol_0, PetscReal *rtol_max, PetscReal *gamma, PetscReal *alpha, PetscReal *alpha2, PetscReal *threshold)
    5616: {
    5617:   SNESKSPEW *kctx;

    5619:   PetscFunctionBegin;
    5621:   kctx = (SNESKSPEW *)snes->kspconvctx;
    5622:   PetscCheck(kctx, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "No Eisenstat-Walker context existing");
    5623:   if (version) *version = kctx->version;
    5624:   if (rtol_0) *rtol_0 = kctx->rtol_0;
    5625:   if (rtol_max) *rtol_max = kctx->rtol_max;
    5626:   if (gamma) *gamma = kctx->gamma;
    5627:   if (alpha) *alpha = kctx->alpha;
    5628:   if (alpha2) *alpha2 = kctx->alpha2;
    5629:   if (threshold) *threshold = kctx->threshold;
    5630:   PetscFunctionReturn(PETSC_SUCCESS);
    5631: }

    5633: PetscErrorCode KSPPreSolve_SNESEW(KSP ksp, Vec b, Vec x, PetscCtx ctx)
    5634: {
    5635:   SNES       snes = (SNES)ctx;
    5636:   SNESKSPEW *kctx = (SNESKSPEW *)snes->kspconvctx;
    5637:   PetscReal  rtol = PETSC_CURRENT, stol;

    5639:   PetscFunctionBegin;
    5640:   if (!snes->ksp_ewconv) PetscFunctionReturn(PETSC_SUCCESS);
    5641:   if (!snes->iter) {
    5642:     rtol = kctx->rtol_0; /* first time in, so use the original user rtol */
    5643:     PetscCall(VecNorm(snes->vec_func, NORM_2, &kctx->norm_first));
    5644:   } else {
    5645:     PetscCheck(kctx->version >= 1 && kctx->version <= 4, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Only versions 1-4 are supported: %" PetscInt_FMT, kctx->version);
    5646:     if (kctx->version == 1) {
    5647:       rtol = PetscAbsReal(snes->norm - kctx->lresid_last) / kctx->norm_last;
    5648:       stol = PetscPowReal(kctx->rtol_last, kctx->alpha2);
    5649:       if (stol > kctx->threshold) rtol = PetscMax(rtol, stol);
    5650:     } else if (kctx->version == 2) {
    5651:       rtol = kctx->gamma * PetscPowReal(snes->norm / kctx->norm_last, kctx->alpha);
    5652:       stol = kctx->gamma * PetscPowReal(kctx->rtol_last, kctx->alpha);
    5653:       if (stol > kctx->threshold) rtol = PetscMax(rtol, stol);
    5654:     } else if (kctx->version == 3) { /* contributed by Luis Chacon, June 2006. */
    5655:       rtol = kctx->gamma * PetscPowReal(snes->norm / kctx->norm_last, kctx->alpha);
    5656:       /* safeguard: avoid sharp decrease of rtol */
    5657:       stol = kctx->gamma * PetscPowReal(kctx->rtol_last, kctx->alpha);
    5658:       stol = PetscMax(rtol, stol);
    5659:       rtol = PetscMin(kctx->rtol_0, stol);
    5660:       /* safeguard: avoid oversolving */
    5661:       stol = kctx->gamma * (kctx->norm_first * snes->rtol) / snes->norm;
    5662:       stol = PetscMax(rtol, stol);
    5663:       rtol = PetscMin(kctx->rtol_0, stol);
    5664:     } else /* if (kctx->version == 4) */ {
    5665:       /* H.-B. An et al. Journal of Computational and Applied Mathematics 200 (2007) 47-60 */
    5666:       PetscReal ared = PetscAbsReal(kctx->norm_last - snes->norm);
    5667:       PetscReal pred = PetscAbsReal(kctx->norm_last - kctx->lresid_last);
    5668:       PetscReal rk   = ared / pred;
    5669:       if (rk < kctx->v4_p1) rtol = 1. - 2. * kctx->v4_p1;
    5670:       else if (rk < kctx->v4_p2) rtol = kctx->rtol_last;
    5671:       else if (rk < kctx->v4_p3) rtol = kctx->v4_m1 * kctx->rtol_last;
    5672:       else rtol = kctx->v4_m2 * kctx->rtol_last;

    5674:       if (kctx->rtol_last_2 > kctx->v4_m3 && kctx->rtol_last > kctx->v4_m3 && kctx->rk_last_2 < kctx->v4_p1 && kctx->rk_last < kctx->v4_p1) rtol = kctx->v4_m4 * kctx->rtol_last;
    5675:       kctx->rtol_last_2 = kctx->rtol_last;
    5676:       kctx->rk_last_2   = kctx->rk_last;
    5677:       kctx->rk_last     = rk;
    5678:     }
    5679:   }
    5680:   /* safeguard: avoid rtol greater than rtol_max */
    5681:   rtol = PetscMin(rtol, kctx->rtol_max);
    5682:   PetscCall(KSPSetTolerances(ksp, rtol, PETSC_CURRENT, PETSC_CURRENT, PETSC_CURRENT));
    5683:   PetscCall(PetscInfo(snes, "iter %" PetscInt_FMT ", Eisenstat-Walker (version %" PetscInt_FMT ") KSP rtol=%g\n", snes->iter, kctx->version, (double)rtol));
    5684:   PetscFunctionReturn(PETSC_SUCCESS);
    5685: }

    5687: PetscErrorCode KSPPostSolve_SNESEW(KSP ksp, Vec b, Vec x, PetscCtx ctx)
    5688: {
    5689:   SNES       snes = (SNES)ctx;
    5690:   SNESKSPEW *kctx = (SNESKSPEW *)snes->kspconvctx;
    5691:   PCSide     pcside;
    5692:   Vec        lres;

    5694:   PetscFunctionBegin;
    5695:   if (!snes->ksp_ewconv) PetscFunctionReturn(PETSC_SUCCESS);
    5696:   PetscCall(KSPGetTolerances(ksp, &kctx->rtol_last, NULL, NULL, NULL));
    5697:   kctx->norm_last = snes->norm;
    5698:   if (kctx->version == 1 || kctx->version == 4) {
    5699:     PC        pc;
    5700:     PetscBool getRes;

    5702:     PetscCall(KSPGetPC(ksp, &pc));
    5703:     PetscCall(PetscObjectTypeCompare((PetscObject)pc, PCNONE, &getRes));
    5704:     if (!getRes) {
    5705:       KSPNormType normtype;

    5707:       PetscCall(KSPGetNormType(ksp, &normtype));
    5708:       getRes = (PetscBool)(normtype == KSP_NORM_UNPRECONDITIONED);
    5709:     }
    5710:     PetscCall(KSPGetPCSide(ksp, &pcside));
    5711:     if (pcside == PC_RIGHT || getRes) { /* KSP residual is true linear residual */
    5712:       PetscCall(KSPGetResidualNorm(ksp, &kctx->lresid_last));
    5713:     } else {
    5714:       /* KSP residual is preconditioned residual */
    5715:       /* compute true linear residual norm */
    5716:       Mat J;
    5717:       PetscCall(KSPGetOperators(ksp, &J, NULL));
    5718:       PetscCall(VecDuplicate(b, &lres));
    5719:       PetscCall(MatMult(J, x, lres));
    5720:       PetscCall(VecAYPX(lres, -1.0, b));
    5721:       PetscCall(VecNorm(lres, NORM_2, &kctx->lresid_last));
    5722:       PetscCall(VecDestroy(&lres));
    5723:     }
    5724:   }
    5725:   PetscFunctionReturn(PETSC_SUCCESS);
    5726: }

    5728: /*@
    5729:   SNESGetKSP - Returns the `KSP` context for a `SNES` solver.

    5731:   Not Collective, but if `snes` is parallel, then `ksp` is parallel

    5733:   Input Parameter:
    5734: . snes - the `SNES` context

    5736:   Output Parameter:
    5737: . ksp - the `KSP` context

    5739:   Level: beginner

    5741:   Notes:
    5742:   The user can then directly manipulate the `KSP` context to set various
    5743:   options, etc.  Likewise, the user can then extract and manipulate the
    5744:   `PC` contexts as well.

    5746:   Some `SNESType`s do not use a `KSP` but a `KSP` is still returned by this function, changes to that `KSP` will have no effect.

    5748: .seealso: [](ch_snes), `SNES`, `KSP`, `PC`, `KSPGetPC()`, `SNESCreate()`, `KSPCreate()`, `SNESSetKSP()`
    5749: @*/
    5750: PetscErrorCode SNESGetKSP(SNES snes, KSP *ksp)
    5751: {
    5752:   PetscFunctionBegin;
    5754:   PetscAssertPointer(ksp, 2);

    5756:   if (!snes->ksp) {
    5757:     PetscCall(KSPCreate(PetscObjectComm((PetscObject)snes), &snes->ksp));
    5758:     PetscCall(PetscObjectIncrementTabLevel((PetscObject)snes->ksp, (PetscObject)snes, 1));

    5760:     PetscCall(KSPSetPreSolve(snes->ksp, KSPPreSolve_SNESEW, snes));
    5761:     PetscCall(KSPSetPostSolve(snes->ksp, KSPPostSolve_SNESEW, snes));

    5763:     PetscCall(KSPMonitorSetFromOptions(snes->ksp, "-snes_monitor_ksp", "snes_preconditioned_residual", snes));
    5764:     PetscCall(PetscObjectSetOptions((PetscObject)snes->ksp, ((PetscObject)snes)->options));
    5765:   }
    5766:   *ksp = snes->ksp;
    5767:   PetscFunctionReturn(PETSC_SUCCESS);
    5768: }

    5770: #include <petsc/private/dmimpl.h>
    5771: /*@
    5772:   SNESSetDM - Sets the `DM` that may be used by some `SNES` nonlinear solvers or their underlying preconditioners

    5774:   Logically Collective

    5776:   Input Parameters:
    5777: + snes - the nonlinear solver context
    5778: - dm   - the `DM`, cannot be `NULL`

    5780:   Level: intermediate

    5782:   Note:
    5783:   A `DM` can only be used for solving one problem at a time because information about the problem is stored on the `DM`,
    5784:   even when not using interfaces like `DMSNESSetFunction()`.  Use `DMClone()` to get a distinct `DM` when solving different
    5785:   problems using the same function space.

    5787: .seealso: [](ch_snes), `DM`, `SNES`, `SNESGetDM()`, `KSPSetDM()`, `KSPGetDM()`
    5788: @*/
    5789: PetscErrorCode SNESSetDM(SNES snes, DM dm)
    5790: {
    5791:   KSP    ksp;
    5792:   DMSNES sdm;

    5794:   PetscFunctionBegin;
    5797:   PetscCall(PetscObjectReference((PetscObject)dm));
    5798:   if (snes->dm) { /* Move the DMSNES context over to the new DM unless the new DM already has one */
    5799:     if (snes->dm->dmsnes && !dm->dmsnes) {
    5800:       PetscCall(DMCopyDMSNES(snes->dm, dm));
    5801:       PetscCall(DMGetDMSNES(snes->dm, &sdm));
    5802:       if (sdm->originaldm == snes->dm) sdm->originaldm = dm; /* Grant write privileges to the replacement DM */
    5803:     }
    5804:     PetscCall(DMCoarsenHookRemove(snes->dm, DMCoarsenHook_SNESVecSol, DMRestrictHook_SNESVecSol, snes));
    5805:     PetscCall(DMDestroy(&snes->dm));
    5806:   }
    5807:   snes->dm     = dm;
    5808:   snes->dmAuto = PETSC_FALSE;

    5810:   PetscCall(SNESGetKSP(snes, &ksp));
    5811:   PetscCall(KSPSetDM(ksp, dm));
    5812:   PetscCall(KSPSetDMActive(ksp, KSP_DMACTIVE_ALL, PETSC_FALSE));
    5813:   if (snes->npc) {
    5814:     PetscCall(SNESSetDM(snes->npc, snes->dm));
    5815:     PetscCall(SNESSetNPCSide(snes, snes->npcside));
    5816:   }
    5817:   PetscFunctionReturn(PETSC_SUCCESS);
    5818: }

    5820: /*@
    5821:   SNESGetDM - Gets the `DM` that may be used by some `SNES` nonlinear solvers/preconditioners

    5823:   Not Collective but `dm` obtained is parallel on `snes`

    5825:   Input Parameter:
    5826: . snes - the `SNES` context

    5828:   Output Parameter:
    5829: . dm - the `DM`

    5831:   Level: intermediate

    5833: .seealso: [](ch_snes), `DM`, `SNES`, `SNESSetDM()`, `KSPSetDM()`, `KSPGetDM()`
    5834: @*/
    5835: PetscErrorCode SNESGetDM(SNES snes, DM *dm)
    5836: {
    5837:   PetscFunctionBegin;
    5839:   if (!snes->dm) {
    5840:     PetscCall(DMShellCreate(PetscObjectComm((PetscObject)snes), &snes->dm));
    5841:     snes->dmAuto = PETSC_TRUE;
    5842:   }
    5843:   *dm = snes->dm;
    5844:   PetscFunctionReturn(PETSC_SUCCESS);
    5845: }

    5847: /*@
    5848:   SNESSetNPC - Sets the nonlinear preconditioner to be used.

    5850:   Collective

    5852:   Input Parameters:
    5853: + snes - iterative context obtained from `SNESCreate()`
    5854: - npc  - the `SNES` nonlinear preconditioner object

    5856:   Options Database Key:
    5857: . -npc_snes_type type - set the type of the `SNES` to use as the nonlinear preconditioner

    5859:   Level: developer

    5861:   Notes:
    5862:   This is rarely used, rather use `SNESGetNPC()` to retrieve the preconditioner and configure it using the API.

    5864:   Only some `SNESType` can use a nonlinear preconditioner

    5866: .seealso: [](ch_snes), `SNES`, `SNESNGS`, `SNESFAS`, `SNESGetNPC()`, `SNESHasNPC()`
    5867: @*/
    5868: PetscErrorCode SNESSetNPC(SNES snes, SNES npc)
    5869: {
    5870:   PetscFunctionBegin;
    5873:   PetscCheckSameComm(snes, 1, npc, 2);
    5874:   PetscCall(PetscObjectReference((PetscObject)npc));
    5875:   PetscCall(SNESDestroy(&snes->npc));
    5876:   snes->npc = npc;
    5877:   PetscFunctionReturn(PETSC_SUCCESS);
    5878: }

    5880: /*@
    5881:   SNESGetNPC - Gets a nonlinear preconditioning solver SNES` to be used to precondition the original nonlinear solver.

    5883:   Not Collective; but any changes to the obtained the `pc` object must be applied collectively

    5885:   Input Parameter:
    5886: . snes - iterative context obtained from `SNESCreate()`

    5888:   Output Parameter:
    5889: . pc - the `SNES` preconditioner context

    5891:   Options Database Key:
    5892: . -npc_snes_type type - set the type of the `SNES` to use as the nonlinear preconditioner

    5894:   Level: advanced

    5896:   Notes:
    5897:   If a `SNES` was previously set with `SNESSetNPC()` then that value is returned, otherwise a new `SNES` object is created that will
    5898:   be used as the nonlinear preconditioner for the current `SNES`.

    5900:   The (preconditioner) `SNES` returned automatically inherits the same nonlinear function and Jacobian supplied to the original
    5901:   `SNES`. These may be overwritten if needed.

    5903:   Use the options database prefixes `-npc_snes`, `-npc_ksp`, etc., to control the configuration of the nonlinear preconditioner

    5905: .seealso: [](ch_snes), `SNESSetNPC()`, `SNESHasNPC()`, `SNES`, `SNESCreate()`
    5906: @*/
    5907: PetscErrorCode SNESGetNPC(SNES snes, SNES *pc)
    5908: {
    5909:   const char *optionsprefix;

    5911:   PetscFunctionBegin;
    5913:   PetscAssertPointer(pc, 2);
    5914:   if (!snes->npc) {
    5915:     PetscCtx ctx;

    5917:     PetscCall(SNESCreate(PetscObjectComm((PetscObject)snes), &snes->npc));
    5918:     PetscCall(PetscObjectIncrementTabLevel((PetscObject)snes->npc, (PetscObject)snes, 1));
    5919:     PetscCall(SNESGetOptionsPrefix(snes, &optionsprefix));
    5920:     PetscCall(SNESSetOptionsPrefix(snes->npc, optionsprefix));
    5921:     PetscCall(SNESAppendOptionsPrefix(snes->npc, "npc_"));
    5922:     if (snes->ops->ctxcompute) {
    5923:       PetscCall(SNESSetComputeApplicationContext(snes, snes->ops->ctxcompute, snes->ops->ctxdestroy));
    5924:     } else {
    5925:       PetscCall(SNESGetApplicationContext(snes, &ctx));
    5926:       PetscCall(SNESSetApplicationContext(snes->npc, ctx));
    5927:     }
    5928:     PetscCall(SNESSetCountersReset(snes->npc, PETSC_FALSE));
    5929:   }
    5930:   *pc = snes->npc;
    5931:   PetscFunctionReturn(PETSC_SUCCESS);
    5932: }

    5934: /*@
    5935:   SNESHasNPC - Returns whether a nonlinear preconditioner is associated with the given `SNES`

    5937:   Not Collective

    5939:   Input Parameter:
    5940: . snes - iterative context obtained from `SNESCreate()`

    5942:   Output Parameter:
    5943: . has_npc - whether the `SNES` has a nonlinear preconditioner or not

    5945:   Level: developer

    5947: .seealso: [](ch_snes), `SNESSetNPC()`, `SNESGetNPC()`
    5948: @*/
    5949: PetscErrorCode SNESHasNPC(SNES snes, PetscBool *has_npc)
    5950: {
    5951:   PetscFunctionBegin;
    5953:   PetscAssertPointer(has_npc, 2);
    5954:   *has_npc = snes->npc ? PETSC_TRUE : PETSC_FALSE;
    5955:   PetscFunctionReturn(PETSC_SUCCESS);
    5956: }

    5958: /*@
    5959:   SNESSetNPCSide - Sets the nonlinear preconditioning side used by the nonlinear preconditioner inside `SNES`.

    5961:   Logically Collective

    5963:   Input Parameter:
    5964: . snes - iterative context obtained from `SNESCreate()`

    5966:   Output Parameter:
    5967: . side - the preconditioning side, where side is one of
    5968: .vb
    5969:       PC_LEFT  - left preconditioning
    5970:       PC_RIGHT - right preconditioning (default for most nonlinear solvers)
    5971: .ve

    5973:   Options Database Key:
    5974: . -snes_npc_side (right|left) - nonlinear preconditioner side

    5976:   Level: intermediate

    5978:   Note:
    5979:   `SNESNRICHARDSON` and `SNESNCG` only support left preconditioning.

    5981: .seealso: [](ch_snes), `SNES`, `SNESGetNPC()`, `SNESNRICHARDSON`, `SNESNCG`, `SNESType`, `SNESGetNPCSide()`, `KSPSetPCSide()`, `PC_LEFT`, `PC_RIGHT`, `PCSide`
    5982: @*/
    5983: PetscErrorCode SNESSetNPCSide(SNES snes, PCSide side)
    5984: {
    5985:   PetscFunctionBegin;
    5988:   if (side == PC_SIDE_DEFAULT) side = PC_RIGHT;
    5989:   PetscCheck((side == PC_LEFT) || (side == PC_RIGHT), PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_WRONG, "Only PC_LEFT and PC_RIGHT are supported");
    5990:   snes->npcside = side;
    5991:   PetscFunctionReturn(PETSC_SUCCESS);
    5992: }

    5994: /*@
    5995:   SNESGetNPCSide - Gets the preconditioning side used by the nonlinear preconditioner inside `SNES`.

    5997:   Not Collective

    5999:   Input Parameter:
    6000: . snes - iterative context obtained from `SNESCreate()`

    6002:   Output Parameter:
    6003: . side - the preconditioning side, where side is one of
    6004: .vb
    6005:       `PC_LEFT` - left preconditioning
    6006:       `PC_RIGHT` - right preconditioning (default for most nonlinear solvers)
    6007: .ve

    6009:   Level: intermediate

    6011: .seealso: [](ch_snes), `SNES`, `SNESGetNPC()`, `SNESSetNPCSide()`, `KSPGetPCSide()`, `PC_LEFT`, `PC_RIGHT`, `PCSide`
    6012: @*/
    6013: PetscErrorCode SNESGetNPCSide(SNES snes, PCSide *side)
    6014: {
    6015:   PetscFunctionBegin;
    6017:   PetscAssertPointer(side, 2);
    6018:   *side = snes->npcside;
    6019:   PetscFunctionReturn(PETSC_SUCCESS);
    6020: }

    6022: /*@
    6023:   SNESSetLineSearch - Sets the `SNESLineSearch` to be used for a given `SNES`

    6025:   Collective

    6027:   Input Parameters:
    6028: + snes       - iterative context obtained from `SNESCreate()`
    6029: - linesearch - the linesearch object

    6031:   Level: developer

    6033:   Note:
    6034:   This is almost never used, rather one uses `SNESGetLineSearch()` to retrieve the line search and set options on it
    6035:   to configure it using the API).

    6037: .seealso: [](ch_snes), `SNES`, `SNESLineSearch`, `SNESGetLineSearch()`
    6038: @*/
    6039: PetscErrorCode SNESSetLineSearch(SNES snes, SNESLineSearch linesearch)
    6040: {
    6041:   PetscFunctionBegin;
    6044:   PetscCheckSameComm(snes, 1, linesearch, 2);
    6045:   PetscCall(PetscObjectReference((PetscObject)linesearch));
    6046:   PetscCall(SNESLineSearchDestroy(&snes->linesearch));

    6048:   snes->linesearch = linesearch;
    6049:   PetscFunctionReturn(PETSC_SUCCESS);
    6050: }