
SSPR2(l) BLAS routine SSPR2(l)
NAME
SSPR2  perform the symmetric rank 2 operation A := alpha*x*y' + alpha*y*x' + A,
SYNOPSIS
SUBROUTINE SSPR2 ( UPLO, N, ALPHA, X, INCX, Y, INCY, AP )
REAL ALPHA
INTEGER INCX, INCY, N
CHARACTER*1 UPLO
REAL AP( * ), X( * ), Y( * )
PURPOSE
SSPR2 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, 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  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.
AP  REAL 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, col
umn 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.
Level 2 Blas routine.
 Written on 22October1986. Jack Dongarra, Argonne National Lab. Jeremy Du
Croz, Nag Central Office. Sven Hammarling, Nag Central Office. Richard Hanson,
Sandia National Labs.
BLAS routine 16 October 1992 SSPR2(l) 
