# zla_lin_berr (3) - Linux Man Pages

zla_lin_berr.f -

## SYNOPSIS

### Functions/Subroutines

subroutine zla_lin_berr (N, NZ, NRHS, RES, AYB, BERR)
ZLA_LIN_BERR computes 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