NAME

       sla_lin_berr.f -

SYNOPSIS

   Functions/Subroutines
       subroutine sla_lin_berr (N, NZ, NRHS, RES, AYB, BERR)
           SLA_LIN_BERR computes a component-wise relative backward error.

Function/Subroutine Documentation

   subroutine sla_lin_berr (integerN, integerNZ, integerNRHS, real, dimension( n, nrhs )RES,
       real, dimension( n, nrhs )AYB, real, dimension( nrhs )BERR)
       SLA_LIN_BERR computes a component-wise relative backward error.

       Purpose:

               SLA_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 REAL 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 sla_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.

       Date:
           September 2012

       Definition at line 102 of file sla_lin_berr.f.

Author

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