dsysv.f(3)

NAME
dsysv.f -

SYNOPSIS

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

Function/Subroutine Documentation

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

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

Purpose:

     DSYSV computes the solution to a real 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.  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.

    A

              A is DOUBLE PRECISION 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
              DSYTRF.

    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 DSYTRF.  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 DOUBLE PRECISION 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 DOUBLE PRECISION 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
              DSYTRF.
              for LWORK < N, TRS will be done with Level BLAS 2
              for LWORK >= N, TRS will be done with Level BLAS 3
              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:
    November 2011

Definition at line 171 of file dsysv.f.

Author

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