Technical Reference: Base Operating System and Extensions, Volume 2

SSYR or DSYR Subroutine

Purpose

Performs the symmetric rank 1 operation.

Library

BLAS Library (libblas.a)

FORTRAN Syntax

SUBROUTINE SSYR(UPLO, N, ALPHA, X, INCX, A, LDA) REAL ALPHA INTEGER INCX, LDA, N CHARACTER*1 UPLO REAL A(LDA,*), X(*)

SUBROUTINE DSYR(UPLO, N, ALPHA,
X, INCX, A, LDA)
DOUBLE PRECISION ALPHA
INTEGER INCX,LDA,N
CHARACTER*1 UPLO
DOUBLE PRECISION A(LDA,*), X(*)

Description

The SSYR or DSYR subroutine 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	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	On entry, N specifies the order of the matrix A; N must be at least 0; unchanged on exit.
ALPHA	On entry, ALPHA specifies the scalar alpha; unchanged on exit.
X	A vector of dimension at least (1 + (N-1) * abs(INCX) ); on entry, the incremented array X must contain the N element vector x; unchanged on exit.
INCX	On entry, INCX specifies the increment for the elements of X; INCX must not be 0; unchanged on exit.
A	An array of dimension ( LDA, N ); on 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. On 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	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.