PlayaPCGSolver.cpp

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// 
//                 Playa: Programmable Linear Algebra
//                 Copyright 2012 Sandia Corporation
// 
// Under the terms of Contract DE-AC04-94AL85000 with Sandia Corporation,
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/* @HEADER@ */


#include "PlayaPCGSolver.hpp"
#include "PlayaOut.hpp"
#include "PlayaTabs.hpp"
#include "PlayaLinearCombinationImpl.hpp"
#include "PlayaSimpleComposedOpImpl.hpp"
#include <iomanip>

using std::setw;

namespace Playa
{

  SolverState<double> PCGSolver::solve(const LinearOperator<double>& A,
               const Vector<double>& b,
               Vector<double>& x) const
  {
    if (precFactory_.ptr().get() == 0)
      {
  return solveUnprec(A, b, x);
      }
    else
      {
  SolverState<double> rtn;
  Preconditioner<double> prec = precFactory_.createPreconditioner(A);
  if (prec.isIdentity())
    {
      rtn = solveUnprec(A, b, x);
    }
  else if (prec.isTwoSided())
    {
      LinearOperator<double> P = prec.left();
      LinearOperator<double> Q = prec.right();
      LinearOperator<double> PAQ = P*A*Q;
      Vector<double> Pb = P*b;
      Vector<double> y;
      rtn = solveUnprec(PAQ, Pb, y);
      x = Q*y;
    }
  else if (prec.hasRight())
    {
      LinearOperator<double> Q = prec.right();
      LinearOperator<double> AQ = A*Q;
      Vector<double> y;
      rtn = solveUnprec(AQ, b, y);
      x = Q*y;
    }
  else if (prec.hasLeft())
    {
      LinearOperator<double> P = prec.left();
      LinearOperator<double> PA = P*A;
      Vector<double> Pb = P*b;
      rtn = solveUnprec(PA, Pb, x);
    }
  else
    {
      TEUCHOS_TEST_FOR_EXCEPTION(true, std::runtime_error,
               "Inconsistent preconditioner state "
               "in PGCSolver::solve()");
    }
  return rtn;
      }
  }
  
  SolverState<double> PCGSolver::solveUnprec(const LinearOperator<double>& A,
               const Vector<double>& b,
               Vector<double>& x) const
  {
    Tabs tab0;
    const ParameterList& params = parameters();
    int verb = 0;
    if (params.isParameter("Verbosity"))
      {
  verb = getParameter<int>(params, "Verbosity");
      }

    int maxIters = getParameter<int>(params, "Max Iterations");
    double tol = getParameter<double>(params, "Tolerance");

    /* Display diagnostic information if needed */
    PLAYA_ROOT_MSG1(verb, tab0 << "Playa CG Solver");
    Tabs tab1;
    PLAYA_ROOT_MSG2(verb, tab0);
    PLAYA_ROOT_MSG2(verb, tab1 << "Verbosity      " << verb);
    PLAYA_ROOT_MSG2(verb, tab1 << "Max Iters      " << maxIters);
    PLAYA_ROOT_MSG2(verb, tab1 << "Tolerance      " << tol);

    /* if the solution vector isn't initialized, set to RHS */
    if (x.ptr().get()==0) x = b.copy();
    
    Vector<double> r = b - A*x;
    Vector<double> p = r.copy();
    double bNorm = b.norm2();
    PLAYA_ROOT_MSG2(verb, tab1 << "Problem size:  " << b.space().dim());
    PLAYA_ROOT_MSG2(verb, tab1 << "||rhs||        " << bNorm);

    /* Prepare the status object to be returned */
    SolverState<double> rtn;
    bool converged = false;
    bool shortcut = false;

    /* Check for zero rhs */
    if (bNorm==0.0)
      {
  PLAYA_ROOT_MSG2(verb, tab1 << "RHS is zero!");
  rtn = SolverState<double>(SolveConverged, "Woo-hoo! Zero RHS shortcut", 
          0, 0.0);
  shortcut = true;
      }

    double rNorm = 0.0;
    double rtr = r*r;

    if (!shortcut)
      {
  PLAYA_ROOT_MSG2(verb, tab1 << endl << tab1 << "CG Loop");

  for (int k=0; k<maxIters; k++)
    {
      Tabs tab2;
      Vector<double> Ap = A*p;
      double alpha = rtr/(p*Ap);
      x += alpha*p;
      r -= alpha*Ap;
      double rtrNew = r*r;
      rNorm = sqrt(rtrNew);
      PLAYA_ROOT_MSG2(verb, tab2 << "iter=" << setw(10) 
          << k << setw(20) << "||r||=" << rNorm);
      /* check relative residual */
      if (rNorm < bNorm*tol) 
        {
    rtn = SolverState<double>(SolveConverged, "Woo-hoo!", 
            k, rNorm);
    converged = true;
    break;
        }
      double beta = rtrNew/rtr;
      rtr = rtrNew;
      p = r + beta*p;
    }
      }

    if (!converged && !shortcut)
      {
  rtn = SolverState<double>(SolveFailedToConverge, 
          "CG failed to converge", 
          maxIters, rNorm);
      }

    PLAYA_ROOT_MSG2(verb, tab0 << endl
        << tab0 << "CG finished with status " 
        << rtn.stateDescription());
    return rtn;
  }


}