NAME

dsyr - perform the symmetric rank 1 operation   A := alpha∗x∗x’ + A

SYNOPSIS

SUBROUTINE DSYR
( UPLO, N, ALPHA, X, INCX, A, LDA )

DOUBLE PRECISION ALPHA

INTEGER INCX, LDA, N

CHARACTER∗1 UPLO

DOUBLE PRECISION A( LDA, ∗ ), X( ∗ )

PURPOSE

DSYR   performs the symmetric rank 1 operation A := alpha∗x∗x’ + A where alpha is a real scalar, x is an n element vector 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  - DOUBLE PRECISION. 
On entry, ALPHA specifies the scalar alpha. Unchanged on exit.

X      - DOUBLE PRECISION 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.

A      - DOUBLE PRECISION 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