Provided by: liblapack-doc_3.3.1-1_all

**NAME**

LAPACK-3 - DLA_LIN_BERR compute 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

**SYNOPSIS**

SUBROUTINE DLA_LIN_BERR ( N, NZ, NRHS, RES, AYB, BERR ) IMPLICIT NONE INTEGER N, NZ, NRHS DOUBLE PRECISION AYB( N, NRHS ), BERR( NRHS ) DOUBLE PRECISION RES( N, NRHS )

**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.

**ARGUMENTS**

N (input) INTEGER The number of linear equations, i.e., the order of the matrix A. N >= 0. NZ (input) 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 (input) INTEGER The number of right hand sides, i.e., the number of columns of the matrices AYB, RES, and BERR. NRHS >= 0. RES (input) DOUBLE PRECISION array, dimension (N,NRHS) The residual matrix, i.e., the matrix R in the relative backward error formula above. AYB (input) 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 (output) DOUBLE PRECISION array, dimension (NRHS) The component-wise relative backward error from the formula above. LAPACK routine (version 3.2.2) April 2011 DLA_LIN_BERR(3lapack)