---
name: "cla_gbamv.f"
section: "3"
platform: "linux"
package: "lapack-doc"
version: "3.12.1-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/cla_gbamv.f"
---

# cla\_gbamv.f(3)

## NAME

SRC/cla\_gbamv.f

## SYNOPSIS

### Functions/Subroutines

subroutine **cla\_gbamv** (trans, m, n, kl, ku, alpha, ab, ldab, x, incx, beta, y, incy)\
 **CLA\_GBAMV** performs a matrix-vector operation to calculate error bounds.

## Function/Subroutine Documentation

### subroutine cla\_gbamv (integer trans, integer m, integer n, integer kl, integer ku, real alpha, complex, dimension( ldab, \* ) ab, integer ldab, complex, dimension( \* ) x, integer incx, real beta, real, dimension( \* ) y, integer incy)

**CLA\_GBAMV** performs a matrix-vector operation to calculate error bounds.

**Purpose:**

```
!>
!> CLA_GBAMV  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**

*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.
!>
```

*KL*

```
!>          KL is INTEGER
!>           The number of subdiagonals within the band of A.  KL >= 0.
!>
```

*KU*

```
!>          KU is INTEGER
!>           The number of superdiagonals within the band of A.  KU >= 0.
!>
```

*ALPHA*

```
!>          ALPHA is REAL
!>           On entry, ALPHA specifies the scalar alpha.
!>           Unchanged on exit.
!>
```

*AB*

```
!>          AB is COMPLEX array, dimension (LDAB,n)
!>           Before entry, the leading m by n part of the array AB must
!>           contain the matrix of coefficients.
!>           Unchanged on exit.
!>
```

*LDAB*

```
!>          LDAB is INTEGER
!>           On entry, LDAB specifies the first dimension of AB as declared
!>           in the calling (sub) program. LDAB must be at least
!>           max( 1, m ).
!>           Unchanged on exit.
!>
```

*X*

```
!>          X is COMPLEX 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 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*

```
!>          Y is REAL array, dimension
!>           ( 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.
!>
```

*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.

Definition at line **186** of file **cla\_gbamv.f**.

## Author

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