# DLA_LIN_BERR (3) - Linux Manuals

dla_lin_berr.f -

## SYNOPSIS

### Functions/Subroutines

subroutine dla_lin_berr (N, NZ, NRHS, RES, AYB, BERR)
DLA_LIN_BERR computes a component-wise relative backward error.

## Function/Subroutine Documentation

### subroutine dla_lin_berr (integerN, integerNZ, integerNRHS, double precision, dimension( n, nrhs )RES, double precision, dimension( n, nrhs )AYB, double precision, dimension( nrhs )BERR)

DLA_LIN_BERR computes a component-wise relative backward error.

Purpose:

```    DLA_LIN_BERR computes component-wise relative backward error from
the formula
max(i) ( abs(R(i)) / ( abs(op(A_s))*abs(Y) + abs(B_s) )(i) )
where abs(Z) is the component-wise absolute value of the matrix
or vector Z.
```

Parameters:

N

```          N is INTEGER
The number of linear equations, i.e., the order of the
matrix A.  N >= 0.
```

NZ

```          NZ is INTEGER
We add (NZ+1)*SLAMCH( 'Safe minimum' ) to R(i) in the numerator to
guard against spuriously zero residuals. Default value is N.
```

NRHS

```          NRHS is INTEGER
The number of right hand sides, i.e., the number of columns
of the matrices AYB, RES, and BERR.  NRHS >= 0.
```

RES

```          RES is DOUBLE PRECISION array, dimension (N,NRHS)
The residual matrix, i.e., the matrix R in the relative backward
error formula above.
```

AYB

```          AYB is DOUBLE PRECISION array, dimension (N, NRHS)
The denominator in the relative backward error formula above, i.e.,
the matrix abs(op(A_s))*abs(Y) + abs(B_s). The matrices A, Y, and B
are from iterative refinement (see dla_gerfsx_extended.f).
```

BERR

```          BERR is DOUBLE PRECISION array, dimension (NRHS)
The component-wise relative backward error from the formula above.
```

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

September 2012

Definition at line 102 of file dla_lin_berr.f.

## Author

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