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( * )
PURPOSE
DSYMV performs the matrix-vector operation
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.
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.