zla_syamv()

subroutine zla_syamv	(	integer	uplo,
		integer	n,
		double precision	alpha,
		complex*16, dimension( lda, * )	a,
		integer	lda,
		complex*16, dimension( * )	x,
		integer	incx,
		double precision	beta,
		double precision, dimension( * )	y,
		integer	incy )

ZLA_SYAMV computes a matrix-vector product using a symmetric indefinite matrix to calculate error bounds.

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

Purpose:

!>
!> ZLA_SYAMV  performs the matrix-vector operation
!>
!>         y := alpha*abs(A)*abs(x) + beta*abs(y),
!>
!> where alpha and beta are scalars, x and y are vectors and A is an
!> n by n symmetric 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]	UPLO	!> UPLO is INTEGER !> On entry, UPLO specifies whether the upper or lower !> triangular part of the array A is to be referenced as !> follows: !> !> UPLO = BLAS_UPPER Only the upper triangular part of A !> is to be referenced. !> !> UPLO = BLAS_LOWER Only the lower triangular part of A !> is to be referenced. !> !> 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 DOUBLE PRECISION . !> On entry, ALPHA specifies the scalar alpha. !> Unchanged on exit. !>
[in]	A	!> A is COMPLEX*16 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, n ). !> Unchanged on exit. !>
[in]	X	!> X is COMPLEX*16 array, dimension at least !> ( 1 + ( n - 1 )*abs( INCX ) ) !> 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 DOUBLE PRECISION . !> 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 DOUBLE PRECISION array, dimension !> ( 1 + ( n - 1 )*abs( INCY ) ) !> 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. !>
[in]	INCY	!> INCY is INTEGER !> On entry, INCY specifies the increment for the elements of !> Y. INCY must not be zero. !> Unchanged on exit. !>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

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.
!>  -- Modified for the absolute-value product, April 2006
!>     Jason Riedy, UC Berkeley
!>