SRC/cspsv.f(3)

NAME
SRC/cspsv.f

SYNOPSIS

  Functions/Subroutines
subroutine cspsv (uplo, n, nrhs, ap, ipiv, b, ldb, info)
CSPSV computes the solution to system of linear equations A * X = B for OTHER matrices

Function/Subroutine Documentation

  subroutine cspsv (character uplo, integer n, integer nrhs, complex, dimension( * ) ap, integer, dimension( * ) ipiv, complex, dimension( ldb, * ) b, integer ldb, integer info)

CSPSV computes the solution to system of linear equations A * X = B for OTHER matrices

Purpose:

     CSPSV computes the solution to a complex system of linear equations
        A * X = B,
     where A is an N-by-N symmetric matrix stored in packed format and X
     and B are N-by-NRHS matrices.
     The diagonal pivoting method is used to factor A as
        A = U * D * U**T,  if UPLO = 'U', or
        A = L * D * L**T,  if UPLO = 'L',
     where U (or L) is a product of permutation and unit upper (lower)
     triangular matrices, D is symmetric and block diagonal with 1-by-1
     and 2-by-2 diagonal blocks.  The factored form of A is then used to
     solve the system of equations A * X = B.

Parameters
    UPLO

              UPLO is CHARACTER*1
              = 'U':  Upper triangle of A is stored;
              = 'L':  Lower triangle of A is stored.

    N

              N is INTEGER
              The number of linear equations, i.e., the order of the
              matrix A.  N >= 0.

    NRHS

              NRHS is INTEGER
              The number of right hand sides, i.e., the number of columns
              of the matrix B.  NRHS >= 0.

    AP

              AP is COMPLEX array, dimension (N*(N+1)/2)
              On entry, the upper or lower triangle of the symmetric matrix
              A, packed columnwise in a linear array.  The j-th column of A
              is stored in the array AP as follows:
              if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j;
              if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = A(i,j) for j<=i<=n.
              See below for further details.
              On exit, the block diagonal matrix D and the multipliers used
              to obtain the factor U or L from the factorization
              A = U*D*U**T or A = L*D*L**T as computed by CSPTRF, stored as
              a packed triangular matrix in the same storage format as A.

    IPIV

              IPIV is INTEGER array, dimension (N)
              Details of the interchanges and the block structure of D, as
              determined by CSPTRF.  If IPIV(k) > 0, then rows and columns
              k and IPIV(k) were interchanged, and D(k,k) is a 1-by-1
              diagonal block.  If UPLO = 'U' and IPIV(k) = IPIV(k-1) < 0,
              then rows and columns k-1 and -IPIV(k) were interchanged and
              D(k-1:k,k-1:k) is a 2-by-2 diagonal block.  If UPLO = 'L' and
              IPIV(k) = IPIV(k+1) < 0, then rows and columns k+1 and
              -IPIV(k) were interchanged and D(k:k+1,k:k+1) is a 2-by-2
              diagonal block.

    B

              B is COMPLEX array, dimension (LDB,NRHS)
              On entry, the N-by-NRHS right hand side matrix B.
              On exit, if INFO = 0, the N-by-NRHS solution matrix X.

    LDB

              LDB is INTEGER
              The leading dimension of the array B.  LDB >= max(1,N).

    INFO

              INFO is INTEGER
              = 0:  successful exit
              < 0:  if INFO = -i, the i-th argument had an illegal value
              > 0:  if INFO = i, D(i,i) is exactly zero.  The factorization
                    has been completed, but the block diagonal matrix D is
                    exactly singular, so the solution could not be
                    computed.

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Further Details:

      The packed storage scheme is illustrated by the following example
      when N = 4, UPLO = 'U':
      Two-dimensional storage of the symmetric matrix A:
         a11 a12 a13 a14
             a22 a23 a24
                 a33 a34     (aij = aji)
                     a44
      Packed storage of the upper triangle of A:
      AP = [ a11, a12, a22, a13, a23, a33, a14, a24, a34, a44 ]

Definition at line 161 of file cspsv.f.

Author

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