ssyr2

SSYR2(1)                         BLAS routine                         SSYR2(1)



NAME
       SSYR2 - performs the symmetric rank 2 operation   A := alpha*x*y' +
       alpha*y*x' + A,

SYNOPSIS
       SUBROUTINE SSYR2(UPLO,N,ALPHA,X,INCX,Y,INCY,A,LDA)

           REAL                                           ALPHA

           INTEGER                                        INCX,INCY,LDA,N

           CHARACTER                                      UPLO

           REAL                                           A(LDA,*),X(*),Y(*)

PURPOSE
       SSYR2  performs the symmetric rank 2 operation

       where alpha is a scalar, x and y are n element vectors and A is an n by
       n symmetric matrix.


ARGUMENTS
       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  - 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.

       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.  Unchanged on exit.

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

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

       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.

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                        SSYR2(1)