NAME

       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 (integer N, integer NZ, integer NRHS, 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

Author

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