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.

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 cla_gerfsx_extended.f).

BERR

          BERR is COMPLEX array, dimension (NRHS)


     The componentwise relative backward error from the formula above.

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

September 2012