sspmv

```SSPMV(1)                         BLAS routine                         SSPMV(1)

NAME
SSPMV - performs the matrix-vector operation   y := alpha*A*x + beta*y,

SYNOPSIS
SUBROUTINE SSPMV(UPLO,N,ALPHA,AP,X,INCX,BETA,Y,INCY)

REAL                                             ALPHA,BETA

INTEGER                                          INCX,INCY,N

CHARACTER                                        UPLO

REAL                                             AP(*),X(*),Y(*)

PURPOSE
SSPMV  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, supplied in packed form.

ARGUMENTS
UPLO   - CHARACTER*1.
On entry, UPLO specifies whether the upper or lower triangular
part of the matrix A is supplied in the packed array AP as
follows:

UPLO = 'U' or 'u'   The upper triangular part of A is supplied
in AP.

UPLO = 'L' or 'l'   The lower triangular part of A is supplied
in AP.

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

AP     - REAL             array of DIMENSION at least
( ( n*( n + 1 ) )/2 ).  Before entry with UPLO = 'U' or 'u', the
array AP must contain the upper triangular part of the symmetric
matrix packed sequentially, column by column, so that AP( 1 )
contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 1, 2 ) and a(
2, 2 ) respectively, and so on.  Before entry with UPLO = 'L' or
'l', the array AP must contain the lower triangular part of the
symmetric matrix packed sequentially, column by column, so that
AP( 1 ) contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 2, 1
) and a( 3, 1 ) respectively, and so on.  Unchanged on exit.

X      - REAL             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   - 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      - REAL             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.

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.

BLAS routine                     November 2008                        SSPMV(1)```