NAME

dsymv - perform the matrix-vector operation   y := alpha∗A∗x + beta∗y

SYNOPSIS

SUBROUTINE DSYMV ( UPLO, N, ALPHA, A, LDA, X, INCX, BETA, Y, INCY )

DOUBLE PRECISION ALPHA, BETA

INTEGER INCX, INCY, LDA, N

CHARACTER∗1 UPLO

DOUBLE PRECISION A( LDA, ∗ ), X( ∗ ), Y( ∗ )

#include <sunperf.h>

void dsymv(char uplo, int n, double alpha, double ∗da, int lda, double ∗dx, int incx, double beta, double ∗dy, int incy) ;

PURPOSE

DSYMV  performs the matrix-vector  operation y := alpha∗A∗x + beta∗y where alpha and beta are scalars, x and y are n element vectors and A is an n by n symmetric matrix. 
 

PARAMETERS

UPLO - CHARACTER∗1. 
On entry, UPLO specifies whether the upper or lower triangular part of the array A is to be referenced as follows:
 
UPLO = ’U’ or ’u’   Only the upper triangular part of A is to be referenced.
 
UPLO = ’L’ or ’l’   Only the lower triangular part of A is to be referenced.
 
Unchanged on exit.

N - INTEGER. 
On entry, N specifies the order of the matrix A. N must be at least zero. Unchanged on exit.

ALPHA - DOUBLE PRECISION. 
On entry, ALPHA specifies the scalar alpha. Unchanged on exit.

A - DOUBLE PRECISION array of DIMENSION ( LDA, n ). 
Before entry with  UPLO = ’U’ or ’u’, the leading n by n upper triangular part of the array A must contain the upper triangular part of the symmetric matrix and the strictly lower triangular part of A is not referenced. Before entry with UPLO = ’L’ or ’l’, the leading n by n lower triangular part of the array A must contain the lower triangular part of the symmetric matrix and the strictly upper triangular part of A is not referenced. Unchanged on exit.

LDA - 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 - DOUBLE PRECISION array of dimension at least
( 1 + ( n - 1 )∗abs( INCX ) ). Before entry, the incremented array X must contain the n element vector x. Unchanged on exit.

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

BETA - 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 - DOUBLE PRECISION array of dimension at least
( 1 + ( n - 1 )∗abs( INCY ) ). Before entry, the incremented array Y must contain the n element vector y. On exit, Y is overwritten by the updated vector y.

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

SunOS 5.0  —  Last change: 10 Dec 1998