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)