DLA_GEAMV (3) Linux Manual Page

dla_geamv.f –

Synopsis

Functions/Subroutines

subroutine dla_geamv (TRANS, M, N, ALPHA, A, LDA, X, INCX, BETA, Y, INCY)
DLA_GEAMV computes a matrix-vector product using a general matrix to calculate error bounds.

Function/Subroutine Documentation

subroutine dla_geamv (integerTRANS, integerM, integerN, double precisionALPHA, double precision, dimension( lda, * )A, integerLDA, double precision, dimension( * )X, integerINCX, double precisionBETA, double precision, dimension( * )Y, integerINCY)

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

Purpose:

 DLA_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,

 "symbolically" zero components are not perturbed. A zero

 entry is considered "symbolic" if all multiplications involved

 in computing that entry have at least one zero multiplicand.

 

Parameters:

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.

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.

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.

ALPHA

 ALPHA is DOUBLE PRECISION

 On entry, ALPHA specifies the scalar alpha.

 Unchanged on exit.

A

 A is DOUBLE PRECISION array of DIMENSION ( LDA, n )

 Before entry, the leading m by n part of the array A must

 contain the matrix of coefficients.

 Unchanged on exit.

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.

X

 X is DOUBLE PRECISION 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.

INCX

 INCX is INTEGER

 On entry, INCX specifies the increment for the elements of

 X. INCX must not be zero.

 Unchanged on exit.

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.

Y

 Y is DOUBLE PRECISION

 Array of 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.

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.

Date:

September 2012

Definition at line 174 of file dla_geamv.f.

Author

Generated automatically by Doxygen for LAPACK from the source code.