csysv_rook.f(3)

NAME
csysv_rook.f -

SYNOPSIS

  Functions/Subroutines

subroutine csysv_rook (UPLO, N, NRHS, A, LDA, IPIV, B, LDB, WORK, LWORK, INFO)
CSYSV_ROOK computes the solution to system of linear equations A * X = B for SY matrices

Function/Subroutine Documentation

  subroutine csysv_rook (characterUPLO, integerN, integerNRHS, complex, dimension( lda, * )A, integerLDA, integer, dimension( * )IPIV, complex, dimension( ldb, * )B, integerLDB, complex, dimension( * )WORK, integerLWORK, integerINFO)

CSYSV_ROOK computes the solution to system of linear equations A * X = B for SY matrices

Purpose:

     CSYSV_ROOK computes the solution to a complex system of linear
     equations
        A * X = B,
     where A is an N-by-N symmetric matrix 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, and D is symmetric and block diagonal with
     1-by-1 and 2-by-2 diagonal blocks.

     CSYTRF_ROOK is called to compute the factorization of a complex
     symmetric matrix A using the bounded Bunch-Kaufman ("rook") diagonal
     pivoting method.

     The factored form of A is then used to solve the system
     of equations A * X = B by calling CSYTRS_ROOK.

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.

    A

              A is COMPLEX array, dimension (LDA,N)
              On entry, the symmetric matrix A.  If UPLO = 'U', the leading
              N-by-N upper triangular part of A contains the upper
              triangular part of the matrix A, and the strictly lower
              triangular part of A is not referenced.  If UPLO = 'L', the
              leading N-by-N lower triangular part of A contains the lower
              triangular part of the matrix A, and the strictly upper
              triangular part of A is not referenced.

              On exit, if INFO = 0, 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
              CSYTRF_ROOK.

    LDA

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

    IPIV

              IPIV is INTEGER array, dimension (N)
              Details of the interchanges and the block structure of D,
              as determined by CSYTRF_ROOK.

              If UPLO = 'U':
                   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 IPIV(k) < 0 and IPIV(k-1) < 0, then rows and
                   columns k and -IPIV(k) were interchanged and rows and
                   columns k-1 and -IPIV(k-1) were inerchaged,
                   D(k-1:k,k-1:k) is a 2-by-2 diagonal block.

              If UPLO = 'L':
                   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 IPIV(k) < 0 and IPIV(k+1) < 0, then rows and
                   columns k and -IPIV(k) were interchanged and rows and
                   columns k+1 and -IPIV(k+1) were inerchaged,
                   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).

    WORK

              WORK is COMPLEX array, dimension (MAX(1,LWORK))
              On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

    LWORK

              LWORK is INTEGER
              The length of WORK.  LWORK >= 1, and for best performance
              LWORK >= max(1,N*NB), where NB is the optimal blocksize for
              CSYTRF_ROOK.

              TRS will be done with Level 2 BLAS

              If LWORK = -1, then a workspace query is assumed; the routine
              only calculates the optimal size of the WORK array, returns
              this value as the first entry of the WORK array, and no error
              message related to LWORK is issued by XERBLA.

    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.

Date:
    April 2012

Contributors:

       April 2012, Igor Kozachenko,
                      Computer Science Division,
                      University of California, Berkeley

      September 2007, Sven Hammarling, Nicholas J. Higham, Craig Lucas,
                      School of Mathematics,
                      University of Manchester

Definition at line 204 of file csysv_rook.f.

Author

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