# zla_lin_berr.f man page

zla_lin_berr.f —

## Synopsis

### Functions/Subroutines

subroutinezla_lin_berr(N, NZ, NRHS, RES, AYB, BERR)ZLA_LIN_BERRcomputes a component-wise relative backward error.

## Function/Subroutine Documentation

### subroutine zla_lin_berr (integerN, integerNZ, integerNRHS, complex*16, dimension( n, nrhs )RES, double precision, dimension( n, nrhs )AYB, double precision, dimension( nrhs )BERR)

**ZLA_LIN_BERR** computes a component-wise relative backward error.

**Purpose:**

```
ZLA_LIN_BERR computes componentwise 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 componentwise 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 zla_gerfsx_extended.f).
```

*BERR*

```
BERR is COMPLEX*16 array, dimension (NRHS)
The componentwise 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 zla_lin_berr.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

zla_lin_berr(3) is an alias of zla_lin_berr.f(3).