NAME

ssyr2 - perform 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∗1 UPLO

REAL A( LDA, ∗ ), X( ∗ ), Y( ∗ )

PURPOSE

SSYR2  performs the symmetric rank 2 operation A := alpha∗x∗y’ + alpha∗y∗x’ + A, where alpha is a scalar, 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  - 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.

SunSoft, Inc.  —  Last change: 27 Jun 1995