SRC/dla_syamv.f(3)

NAME
SRC/dla_syamv.f

SYNOPSIS

  Functions/Subroutines
subroutine dla_syamv (uplo, n, alpha, a, lda, x, incx, beta, y, incy)
DLA_SYAMV computes a matrix-vector product using a symmetric indefinite matrix to calculate error bounds.

Function/Subroutine Documentation

  subroutine dla_syamv (integer uplo, integer n, double precision alpha, double precision, dimension( lda, * ) a, integer lda, double precision, dimension( * ) x, integer incx, double precision beta, double precision, dimension( * ) y, integer incy)

DLA_SYAMV computes a matrix-vector product using a symmetric indefinite matrix to calculate error bounds.

Purpose:

    !>
    !> DLA_SYAMV  performs the matrix-vector operation
    !>
    !>         y := alpha*abs(A)*abs(x) + beta*abs(y),
    !>
    !> where alpha and beta are scalars, x and y are vectors and A is an
    !> n by n symmetric matrix.
    !>
    !> This function is primarily used in calculating error bounds.
    !> To protect against underflow during evaluation, components in
    !> the resulting vector are perturbed away from zero by (N+1)
    !> times the underflow threshold.  To prevent unnecessarily large
    !> errors for block-structure embedded in general matrices,
    !>  zero components are not perturbed.  A zero
    !> entry is considered  if all multiplications involved
    !> in computing that entry have at least one zero multiplicand.
    !>

Parameters
    UPLO

    !>          UPLO is INTEGER
    !>           On entry, UPLO specifies whether the upper or lower
    !>           triangular part of the array A is to be referenced as
    !>           follows:
    !>
    !>              UPLO = BLAS_UPPER   Only the upper triangular part of A
    !>                                  is to be referenced.
    !>
    !>              UPLO = BLAS_LOWER   Only the lower triangular part of A
    !>                                  is to be referenced.
    !>
    !>           Unchanged on exit.
    !>

    N

    !>          N is INTEGER
    !>           On entry, N specifies the number of columns of the matrix A.
    !>           N must be at least zero.
    !>           Unchanged on exit.
    !>

    ALPHA

    !>          ALPHA is DOUBLE PRECISION .
    !>           On entry, ALPHA specifies the scalar alpha.
    !>           Unchanged on exit.
    !>

    A

    !>          A is DOUBLE PRECISION array, dimension ( LDA, n ).
    !>           Before entry, the leading m by n part of the array A must
    !>           contain the matrix of coefficients.
    !>           Unchanged on exit.
    !>

    LDA

    !>          LDA is INTEGER
    !>           On entry, LDA specifies the first dimension of A as declared
    !>           in the calling (sub) program. LDA must be at least
    !>           max( 1, n ).
    !>           Unchanged on exit.
    !>

    X

    !>          X is DOUBLE PRECISION array, dimension
    !>           ( 1 + ( n - 1 )*abs( INCX ) )
    !>           Before entry, the incremented array X must contain the
    !>           vector x.
    !>           Unchanged on exit.
    !>

    INCX

    !>          INCX is INTEGER
    !>           On entry, INCX specifies the increment for the elements of
    !>           X. INCX must not be zero.
    !>           Unchanged on exit.
    !>

    BETA

    !>          BETA is DOUBLE PRECISION .
    !>           On entry, BETA specifies the scalar beta. When BETA is
    !>           supplied as zero then Y need not be set on input.
    !>           Unchanged on exit.
    !>

    Y

    !>          Y is DOUBLE PRECISION array, dimension
    !>           ( 1 + ( n - 1 )*abs( INCY ) )
    !>           Before entry with BETA non-zero, the incremented array Y
    !>           must contain the vector y. On exit, Y is overwritten by the
    !>           updated vector y.
    !>

    INCY

    !>          INCY is INTEGER
    !>           On entry, INCY specifies the increment for the elements of
    !>           Y. INCY must not be zero.
    !>           Unchanged on exit.
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Further Details:

    !>
    !>  Level 2 Blas routine.
    !>
    !>  -- Written on 22-October-1986.
    !>     Jack Dongarra, Argonne National Lab.
    !>     Jeremy Du Croz, Nag Central Office.
    !>     Sven Hammarling, Nag Central Office.
    !>     Richard Hanson, Sandia National Labs.
    !>  -- Modified for the absolute-value product, April 2006
    !>     Jason Riedy, UC Berkeley
    !>

Definition at line 175 of file dla_syamv.f.

Author

Generated automatically by Doxygen for LAPACK from the source code.