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# cla_gbamv.3lapack

Langue: *en*

Version: *277657 (debian - 07/07/09)*

Section: *3 (Bibliothèques de fonctions)*

## NAME

CLA_GBAMV - performs one of the matrix-vector operations y := alpha*abs(A)*abs(x) + beta*abs(y),## SYNOPSIS

- SUBROUTINE CLA_GBAMV(
- TRANS, M, N, KL, KU, ALPHA, AB, LDAB, X, INCX, BETA, Y, INCY )

- IMPLICIT NONE

- REAL ALPHA, BETA

- INTEGER INCX, INCY, LDAB, M, N, KL, KU, TRANS

- COMPLEX AB( LDAB, * ), X( * )

- REAL Y( * )

## PURPOSE

SLA_GEAMV performs one of the matrix-vector operationsor y := alpha*abs(A)'*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.

## ARGUMENTS

- TRANS - 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')*abs(x) + beta*abs(y)

BLAS_CONJ_TRANS y := alpha*abs(A')*abs(x) + beta*abs(y) Unchanged on exit.- M - INTEGER
- On entry, M specifies the number of rows of the matrix A. M must be at least zero. Unchanged on exit.
- N - INTEGER
- On entry, N specifies the number of columns of the matrix A. N must be at least zero. Unchanged on exit.
- KL - INTEGER
- The number of subdiagonals within the band of A. KL >= 0.
- KU - INTEGER
- The number of superdiagonals within the band of A. KU >= 0.
- ALPHA - REAL
- On entry, ALPHA specifies the scalar alpha. Unchanged on exit.
- A - REAL 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 - 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 - REAL array of DIMENSION at least
- ( 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 - INTEGER
- On entry, INCX specifies the increment for the elements of X. INCX must not be zero. Unchanged on exit.
- BETA - 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.
- Y - REAL 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 - INTEGER
- On entry, INCY specifies the increment for the elements of Y. INCY must not be zero. Unchanged on exit. Level 2 Blas routine.

Contenus ©2006-2020 Benjamin Poulain

Design ©2006-2020 Maxime Vantorre