man ssyr2 (Fonctions bibliothèques) - perform the symmetric rank 2 operation A := alpha*x*y' + alpha*y*x' + A,
NAME
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 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.
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.