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compute_residual.cpp
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compute_residual.cpp
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//@HEADER
// ************************************************************************
//
// HPCCG: Simple Conjugate Gradient Benchmark Code
// Copyright (2006) Sandia Corporation
//
// Under terms of Contract DE-AC04-94AL85000, there is a non-exclusive
// license for use of this work by or on behalf of the U.S. Government.
//
// This library is free software; you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as
// published by the Free Software Foundation; either version 2.1 of the
// License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
// USA
// Questions? Contact Michael A. Heroux ([email protected])
//
// ************************************************************************
//@HEADER
/////////////////////////////////////////////////////////////////////////
// Routine to compute the 1-norm difference between two vectors where:
// n - number of vector elements (on this processor)
// v1, v2 - input vectors
// residual - pointer to scalar value, on exit will contain result.
/////////////////////////////////////////////////////////////////////////
#include <cmath> // needed for fabs
using std::fabs;
#include "compute_residual.hpp"
int compute_residual(const int n, const double * const v1,
const double * const v2, double * const residual)
{
double local_residual = 0.0;
for (int i=0; i<n; i++) {
double diff = fabs(v1[i] - v2[i]);
if (diff > local_residual) local_residual = diff;
}
#ifdef USING_MPI
// Use MPI's reduce function to collect all partial sums
double global_residual = 0;
MPI_Allreduce(&local_residual, &global_residual, 1, MPI_DOUBLE, MPI_MAX,
MPI_COMM_WORLD);
*residual = global_residual;
#else
*residual = local_residual;
#endif
return(0);
}