Date: 2026-07-30T21:14:06+00:00

Actual source code: ex1.c

      1: static char help[] = "Tests VecView() contour plotting for 2d DMDAs.\n\n";

      3: /*
      4:   MATLAB must be installed to configure PETSc to have MATLAB engine.
      5: Unless you have specific important reasons for using the MATLAB engine, we do not
      6: recommend it. If you want to use MATLAB for visualization and maybe a little post processing
      7: then you can use the socket viewer and send the data to MATLAB via that.

      9:   VecView() on DMDA vectors first puts the Vec elements into global natural ordering before printing (or plotting)
     10: them. In 2d 5 by 2 DMDA this means the numbering is

     12:      5  6   7   8   9
     13:      0  1   2   3   4

     15: Now the default split across 2 processors with the DM  is (by rank)

     17:     0  0   0  1   1
     18:     0  0   0  1   1

     20: So the global PETSc ordering is

     22:     3  4  5   8  9
     23:     0  1  2   6  7

     25: Use the options
     26:      -da_grid_x <nx> - number of grid points in x direction, if M < 0
     27:      -da_grid_y <ny> - number of grid points in y direction, if N < 0
     28:      -da_processors_x <MX> number of processors in x directio
     29:      -da_processors_y <MY> number of processors in x direction
     30: */

     32: #include <petscdm.h>
     33: #include <petscdmda.h>

     35: int main(int argc, char **argv)
     36: {
     37:   PetscMPIInt     rank;
     38:   PetscInt        M = 10, N = 8;
     39:   PetscBool       flg = PETSC_FALSE;
     40:   DM              da;
     41:   PetscViewer     viewer;
     42:   Vec             local, global;
     43:   PetscScalar     value;
     44:   DMBoundaryType  bx = DM_BOUNDARY_NONE, by = DM_BOUNDARY_NONE;
     45:   DMDAStencilType stype = DMDA_STENCIL_BOX;
     46: #if defined(PETSC_HAVE_MATLAB)
     47:   PetscViewer mviewer;
     48:   PetscMPIInt size;
     49: #endif

     51:   PetscFunctionBeginUser;
     52:   PetscCall(PetscInitialize(&argc, &argv, NULL, help));
     53:   PetscCall(PetscViewerDrawOpen(PETSC_COMM_WORLD, 0, "", 300, 0, 300, 300, &viewer));
     54: #if defined(PETSC_HAVE_MATLAB)
     55:   PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
     56:   if (size == 1) PetscCall(PetscViewerMatlabOpen(PETSC_COMM_WORLD, "tmp.mat", FILE_MODE_WRITE, &mviewer));
     57: #endif

     59:   PetscCall(PetscOptionsGetBool(NULL, NULL, "-star_stencil", &flg, NULL));
     60:   if (flg) stype = DMDA_STENCIL_STAR;

     62:   /* Create distributed array and get vectors */
     63:   PetscCall(DMDACreate2d(PETSC_COMM_WORLD, bx, by, stype, M, N, PETSC_DECIDE, PETSC_DECIDE, 1, 1, NULL, NULL, &da));
     64:   PetscCall(DMSetFromOptions(da));
     65:   PetscCall(DMSetUp(da));
     66:   PetscCall(DMCreateGlobalVector(da, &global));
     67:   PetscCall(DMCreateLocalVector(da, &local));

     69:   value = -3.0;
     70:   PetscCall(VecSet(global, value));
     71:   PetscCall(DMGlobalToLocalBegin(da, global, INSERT_VALUES, local));
     72:   PetscCall(DMGlobalToLocalEnd(da, global, INSERT_VALUES, local));

     74:   PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
     75:   value = rank + 1;
     76:   PetscCall(VecScale(local, value));
     77:   PetscCall(DMLocalToGlobalBegin(da, local, ADD_VALUES, global));
     78:   PetscCall(DMLocalToGlobalEnd(da, local, ADD_VALUES, global));

     80:   flg = PETSC_FALSE;
     81:   PetscCall(PetscOptionsGetBool(NULL, NULL, "-view_global", &flg, NULL));
     82:   if (flg) { /* view global vector in natural ordering */
     83:     PetscCall(VecView(global, PETSC_VIEWER_STDOUT_WORLD));
     84:   }
     85:   PetscCall(DMView(da, viewer));
     86:   PetscCall(VecView(global, viewer));
     87: #if defined(PETSC_HAVE_MATLAB)
     88:   if (size == 1) {
     89:     PetscCall(DMView(da, mviewer));
     90:     PetscCall(VecView(global, mviewer));
     91:   }
     92: #endif

     94:   /* Free memory */
     95: #if defined(PETSC_HAVE_MATLAB)
     96:   if (size == 1) PetscCall(PetscViewerDestroy(&mviewer));
     97: #endif
     98:   PetscCall(PetscViewerDestroy(&viewer));
     99:   PetscCall(VecDestroy(&local));
    100:   PetscCall(VecDestroy(&global));
    101:   PetscCall(DMDestroy(&da));
    102:   PetscCall(PetscFinalize());
    103:   return 0;
    104: }

    106: /*TEST

    108:    test:
    109:       requires: x
    110:       nsize: 2
    111:       args: -nox
    112:       output_file: output/empty.out

    114: TEST*/