sspr

SSPR(1)                          BLAS routine                          SSPR(1)



NAME
       SSPR - performs the symmetric rank 1 operation   A := alpha*x*x' + A,

SYNOPSIS
       SUBROUTINE SSPR(UPLO,N,ALPHA,X,INCX,AP)

           REAL                                ALPHA

           INTEGER                             INCX,N

           CHARACTER                           UPLO

           REAL                                AP(*),X(*)

PURPOSE
       SSPR    performs the symmetric rank 1 operation

       where alpha is a real scalar, x is an n element vector 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.

       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.

       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. On exit, the array AP
              is overwritten by the upper triangular part of the updated
              matrix.  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. On exit, the array AP is overwritten by
              the lower triangular part of the updated matrix.

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                         SSPR(1)