SSYR2 - perform 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*1 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.
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 - 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 vec
tor x. Unchanged on exit.
INCX - INTEGER.
On entry, INCX specifies the increment for the ele
ments of X. INCX must not be zero. Unchanged on
exit.
( 1 + ( n - 1 )*abs( INCY ) ). Before entry, the
incremented array Y must contain the n element vec
tor y. Unchanged on exit.
INCY - INTEGER.
On entry, INCY specifies the increment for the ele
ments 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 con
tain 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.
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.
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