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, column 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 22-October-1986. Jack Dongarra, Argonne National Lab. Jeremy
Du Croz, Nag Central Office. Sven Hammarling, Nag Central Office. Richard
Hanson, Sandia National Labs.