EstimateError.F

#include "parmdefines.h"
c**********************************************************************
#include "author.inc"
c*    $Id: EstimateError.F,v 1.1 1996/04/28 20:14:54 turner Exp $
c*
c*    Computes error estimate based on various norms.
c*
c*    <PARAMETER LIST>
c*
c*     Input:
c*      anorm - norm of coefficient
c*      xnorm - norm of unknown vector
c*      bnorm - norm of right-hand-side
c*      rnorm - norm of residual vector
c*      rnormt0 - norm of initial residual vector
c*
c*     Output:
c*      err - error estimate
c*      status - return status:
c*         0  ==>  convergence was achieved
c*
#include "parmdesc.inc"
c*
#include "copyright.inc"
c**********************************************************************
      subroutine JT_EstimateError (stop, anorm, xnorm, bnorm, rnorm,
     &           rnormt0, err, status)
      implicit none
c
c ... Input:
      integer stop
      real anorm, xnorm, bnorm, rnorm, rnormt0
c
c ... Output:
      integer status
      real err
c
c ... Local:
      real zero
c
      parameter (zero=0.0d0)
c
      if (stop .eq. _JT_stop_axb_) then
c
c      Use || r || / ( || A ||*|| x || + || b || )
       if (xnorm.eq.zero .and. bnorm.eq.zero) then
        err = zero
       else
        err = rnorm / (anorm*xnorm + bnorm)
       endif
      elseif (stop .eq. _JT_stop_b_) then
c
c      Use || r || / || b ||
       err = rnorm/bnorm
      elseif (stop .eq. _JT_stop_x_) then
c
c      Use || r || / || x ||
       err = rnorm
       if (xnorm .ne. zero) err = err/xnorm
      elseif (stop .eq. _JT_stop_r0_) then
c
c      Use || r || / || b - Ax0 ||
       err = rnorm/rnormt0
      elseif (stop .eq. _JT_stop_r_) then
c
c      Use || r ||
       err = rnorm
      endif
c
      status = 0
      return
      end