sla_syamv.f man page

sla_syamv.f —

Synopsis

Functions/Subroutines

subroutine sla_syamv (UPLO, N, ALPHA, A, LDA, X, INCX, BETA, Y, INCY)
SLA_SYAMV computes a matrix-vector product using a symmetric indefinite matrix to calculate error bounds.

Function/Subroutine Documentation

subroutine sla_syamv (integerUPLO, integerN, realALPHA, real, dimension( lda, * )A, integerLDA, real, dimension( * )X, integerINCX, realBETA, real, dimension( * )Y, integerINCY)

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

Purpose:

SLA_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,
"symbolically" zero components are not perturbed.  A zero
entry is considered "symbolic" 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 REAL .
 On entry, ALPHA specifies the scalar alpha.
 Unchanged on exit.

A

A is REAL array of 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 REAL 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 REAL .
 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 REAL 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.

Date:

September 2012

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 177 of file sla_syamv.f.

Author

Generated automatically by Doxygen for LAPACK from the source code.

Referenced By

sla_syamv(3) is an alias of sla_syamv.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK