sla_geamv()

subroutine sla_geamv	(	integer	trans,
		integer	m,
		integer	n,
		real	alpha,
		real, dimension( lda, * )	a,
		integer	lda,
		real, dimension( * )	x,
		integer	incx,
		real	beta,
		real, dimension( * )	y,
		integer	incy )

SLA_GEAMV computes a matrix-vector product using a general matrix to calculate error bounds.

Download SLA_GEAMV + dependencies [TGZ] [ZIP] [TXT]

Purpose:

!>
!> SLA_GEAMV  performs one of the matrix-vector operations
!>
!>         y := alpha*abs(A)*abs(x) + beta*abs(y),
!>    or   y := alpha*abs(A)**T*abs(x) + beta*abs(y),
!>
!> where alpha and beta are scalars, x and y are vectors and A is an
!> m by n matrix.
!>
!> This function is primarily used in calculating error bounds.
!> To protect against underflow during evaluation, components in
!> the resulting vector are perturbed away from zero by (N+1)
!> times the underflow threshold.  To prevent unnecessarily large
!> errors for block-structure embedded in general matrices,
!>  zero components are not perturbed.  A zero
!> entry is considered  if all multiplications involved
!> in computing that entry have at least one zero multiplicand.
!> 

Parameters

[in]	TRANS	!> TRANS is INTEGER !> On entry, TRANS specifies the operation to be performed as !> follows: !> !> BLAS_NO_TRANS y := alpha*abs(A)*abs(x) + beta*abs(y) !> BLAS_TRANS y := alpha*abs(A**T)*abs(x) + beta*abs(y) !> BLAS_CONJ_TRANS y := alpha*abs(A**T)*abs(x) + beta*abs(y) !> !> Unchanged on exit. !>
[in]	M	!> M is INTEGER !> On entry, M specifies the number of rows of the matrix A. !> M must be at least zero. !> Unchanged on exit. !>
[in]	N	!> N is INTEGER !> On entry, N specifies the number of columns of the matrix A. !> N must be at least zero. !> Unchanged on exit. !>
[in]	ALPHA	!> ALPHA is REAL !> On entry, ALPHA specifies the scalar alpha. !> Unchanged on exit. !>
[in]	A	!> A is REAL array, dimension ( LDA, n ) !> Before entry, the leading m by n part of the array A must !> contain the matrix of coefficients. !> Unchanged on exit. !>
[in]	LDA	!> LDA is INTEGER !> On entry, LDA specifies the first dimension of A as declared !> in the calling (sub) program. LDA must be at least !> max( 1, m ). !> Unchanged on exit. !>
[in]	X	!> X is REAL array, dimension !> ( 1 + ( n - 1 )*abs( INCX ) ) when TRANS = 'N' or 'n' !> and at least !> ( 1 + ( m - 1 )*abs( INCX ) ) otherwise. !> Before entry, the incremented array X must contain the !> vector x. !> Unchanged on exit. !>
[in]	INCX	!> INCX is INTEGER !> On entry, INCX specifies the increment for the elements of !> X. INCX must not be zero. !> Unchanged on exit. !>
[in]	BETA	!> BETA is REAL !> On entry, BETA specifies the scalar beta. When BETA is !> supplied as zero then Y need not be set on input. !> Unchanged on exit. !>
[in,out]	Y	!> Y is REAL array, !> dimension at least !> ( 1 + ( m - 1 )*abs( INCY ) ) when TRANS = 'N' or 'n' !> and at least !> ( 1 + ( n - 1 )*abs( INCY ) ) otherwise. !> Before entry with BETA non-zero, the incremented array Y !> must contain the vector y. On exit, Y is overwritten by the !> updated vector y. !> If either m or n is zero, then Y not referenced and the function !> performs a quick return. !>
[in]	INCY	!> INCY is INTEGER !> On entry, INCY specifies the increment for the elements of !> Y. INCY must not be zero. !> Unchanged on exit. !> !> Level 2 Blas routine. !>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.