NAME

dspr2 - perform the symmetric rank 2 operation   A := alpha∗x∗y’ + alpha∗y∗x’ + A

SYNOPSIS

SUBROUTINE DSPR2 ( UPLO, N, ALPHA, X, INCX, Y, INCY, AP )

DOUBLE PRECISION ALPHA

INTEGER INCX, INCY, N

CHARACTER∗1 UPLO

DOUBLE PRECISION AP( ∗ ), X( ∗ ), Y( ∗ )

#include <sunperf.h>

void dspr2(char uplo, int n, double alpha, double ∗dx, int incx, double ∗dy, int incy, double ∗ap) ;

PURPOSE

DSPR2  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, supplied in packed form. 
 

PARAMETERS

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 - 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.

Y - DOUBLE PRECISION 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.

AP - DOUBLE PRECISION 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.

SunOS 5.0  —  Last change: 10 Dec 1998