SSYR2(1) BLAS routine SSYR2(1)NAME
SSYR2 - performs the symmetric rank 2 operation A := alpha*x*y' +
alpha*y*x' + A,
SYNOPSIS
SUBROUTINE SSYR2(UPLO,N,ALPHA,X,INCX,Y,INCY,A,LDA)
REAL ALPHA
INTEGER INCX,INCY,LDA,N
CHARACTER UPLO
REAL A(LDA,*),X(*),Y(*)
PURPOSE
SSYR2 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.
ARGUMENTS
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 - 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.
A - REAL 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.
FURTHER DETAILS
Level 2 Blas routine.
-- Written on 22-October-1986.
Jack Dongarra, Argonne National Lab.
Jeremy Du Croz, Nag Central Office.
Sven Hammarling, Nag Central Office.
Richard Hanson, Sandia National Labs.
BLAS routine November 2008 SSYR2(1)
