# cla_lin_berr.f - Man Page

SRC/cla_lin_berr.f

## Synopsis

### Functions/Subroutines

subroutine **cla_lin_berr** (n, nz, nrhs, res, ayb, berr)**CLA_LIN_BERR** computes a component-wise relative backward error.

## Function/Subroutine Documentation

### subroutine cla_lin_berr (integer n, integer nz, integer nrhs, complex, dimension( n, nrhs ) res, real, dimension( n, nrhs ) ayb, real, dimension( nrhs ) berr)

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

**Purpose:**

CLA_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 COMPLEX array, dimension (N,NRHS) The residual matrix, i.e., the matrix R in the relative backward error formula above.

*AYB*AYB is REAL 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 cla_gerfsx_extended.f).

*BERR*BERR is REAL 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.

Definition at line **100** of file **cla_lin_berr.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page cla_lin_berr(3) is an alias of cla_lin_berr.f(3).

Tue Nov 28 2023 12:08:41 Version 3.12.0 LAPACK