# dla_lin_berr.f - Man Page

## 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 (integer N, integer NZ, integer NRHS, 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:**December 2016

Definition at line 103 of file dla_lin_berr.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

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

Tue Nov 14 2017 Version 3.8.0 LAPACK