cla_lin_berr.f - Man Page

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

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.