---
name: "cla_geamv"
section: "3lapack"
platform: "linux"
package: "liblapack-doc"
version: "3.2.1-8"
release: "Debian 6.0 (Squeeze)"
platforms: ["linux"]
url: "https://new.carta.tech/cla_geamv/3lapack"
---

# cla\_geamv(3lapack)

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

## NAME

CLA\_GEAMV - performs one of the matrix-vector operations   y := alpha\*abs(A)\*abs(x) + beta\*abs(y),

## SYNOPSIS

- SUBROUTINE CLA\_GEAMV

  ( TRANS, M, N, ALPHA, A, LDA, X, INCX, BETA, Y, INCY )

- IMPLICIT

  NONE

- REAL

  ALPHA, BETA

- INTEGER

  INCX, INCY, LDA, M, N

- INTEGER

  TRANS

- COMPLEX

  A( LDA, \* ), X( \* )

- REAL

  Y( \* )

## PURPOSE

CLA\_GEAMV  performs one of the matrix-vector operations\
    or   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.

- ALPHA - REAL

  On entry, ALPHA specifies the scalar alpha. Unchanged on exit.

- A - COMPLEX 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 - COMPLEX 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.