
DSYR2(l) BLAS routine DSYR2(l)
NAME
DSYR2  perform the symmetric rank 2 operation A := alpha*x*y' + alpha*y*x' + A,
SYNOPSIS
SUBROUTINE DSYR2 ( UPLO, N, ALPHA, X, INCX, Y, INCY, A, LDA )
DOUBLE PRECISION ALPHA
INTEGER INCX, INCY, LDA, N
CHARACTER*1 UPLO
DOUBLE PRECISION A( LDA, * ), X( * ), Y( * )
PURPOSE
DSYR2 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.
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.
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.
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 triangu
lar 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.
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 DSYR2(l) 
