BelosTFQMRIter.hpp

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// @HEADER
// *****************************************************************************
//                 Belos: Block Linear Solvers Package
//
// Copyright 2004-2016 NTESS and the Belos contributors.
// SPDX-License-Identifier: BSD-3-Clause
// *****************************************************************************
// @HEADER
//
// This file contains an implementation of the TFQMR iteration
// for solving non-Hermitian linear systems of equations Ax = b, 
// where b is a single-vector and x is the corresponding solution.
//
// The implementation is a slight modification on the TFQMR iteration
// found in Saad's "Iterative Methods for Sparse Linear Systems".
//
 
#ifndef BELOS_TFQMR_ITER_HPP
#define BELOS_TFQMR_ITER_HPP
 
#include "BelosConfigDefs.hpp"
#include "BelosIteration.hpp"
#include "BelosTypes.hpp" 
 
#include "BelosLinearProblem.hpp"
#include "BelosOutputManager.hpp"
#include "BelosStatusTest.hpp"
#include "BelosOperatorTraits.hpp"
#include "BelosMultiVecTraits.hpp"
 
#include "Teuchos_ScalarTraits.hpp"
#include "Teuchos_ParameterList.hpp"
#include "Teuchos_TimeMonitor.hpp"
 
namespace Belos {
 
  template <class ScalarType, class MV>
  struct TFQMRIterState {
 
    Teuchos::RCP<const MV> R;
    Teuchos::RCP<const MV> W;
    Teuchos::RCP<const MV> U;
    Teuchos::RCP<const MV> Rtilde;
    Teuchos::RCP<const MV> D;
    Teuchos::RCP<const MV> V;
 
    TFQMRIterState() : R(Teuchos::null), W(Teuchos::null), U(Teuchos::null),
                       Rtilde(Teuchos::null), D(Teuchos::null), V(Teuchos::null)
    {}
  };
 
  
 
  
  class TFQMRIterateFailure : public BelosError {public:
    TFQMRIterateFailure(const std::string& what_arg) : BelosError(what_arg)
    {}};
  
 
  template<class ScalarType, class MV, class OP, class DM>
  class TFQMRIter : public Iteration<ScalarType,MV,OP,DM> { 
  public:
    //
    // Convenience typedefs
    //
    typedef MultiVecTraits<ScalarType,MV,DM> MVT;
    typedef OperatorTraits<ScalarType,MV,OP> OPT;
    typedef Teuchos::ScalarTraits<ScalarType> SCT;
    typedef typename SCT::magnitudeType MagnitudeType;
    
 
 
    TFQMRIter( const Teuchos::RCP<LinearProblem<ScalarType,MV,OP,DM> > &problem,
         const Teuchos::RCP<OutputManager<ScalarType> > &printer,
         const Teuchos::RCP<StatusTest<ScalarType,MV,OP,DM> > &tester,
         Teuchos::ParameterList &params );
    
    virtual ~TFQMRIter() {};
  
 
 
    
    void iterate();
 
    void initializeTFQMR(const TFQMRIterState<ScalarType,MV> & newstate);
    
    void initialize()
    {
      TFQMRIterState<ScalarType,MV> empty;
      initializeTFQMR(empty);
    }
    
    TFQMRIterState<ScalarType,MV> getState() const {
      TFQMRIterState<ScalarType,MV> state;
      state.R = R_;
      state.W = W_;
      state.U = U_;
      state.Rtilde = Rtilde_;
      state.D = D_;
      state.V = V_;
      state.solnUpdate = solnUpdate_;
      return state;
    }
    
    
    
 
    
    int getNumIters() const { return iter_; }
    
    void resetNumIters( int iter = 0 ) { iter_ = iter; }
    
    Teuchos::RCP<const MV> getNativeResiduals( std::vector<MagnitudeType> *norms ) const;
    
 
    Teuchos::RCP<MV> getCurrentUpdate() const { return solnUpdate_; }
 
 
 
 
    
    const LinearProblem<ScalarType,MV,OP,DM>& getProblem() const { return *lp_; }
    
    int getBlockSize() const { return 1; }
    
    void setBlockSize(int blockSize) {
      TEUCHOS_TEST_FOR_EXCEPTION(blockSize!=1,std::invalid_argument,
                       "Belos::TFQMRIter::setBlockSize(): Cannot use a block size that is not one.");
    }
    
    bool isInitialized() { return initialized_; }
    
    
  
  private:
 
    //
    // Internal methods
    //
    void setStateSize();
    
    //
    // Classes inputed through constructor that define the linear problem to be solved.
    //
    const Teuchos::RCP<LinearProblem<ScalarType,MV,OP,DM> >    lp_;
    const Teuchos::RCP<OutputManager<ScalarType> >          om_;
    const Teuchos::RCP<StatusTest<ScalarType,MV,OP,DM> >       stest_;
    
    //
    // Algorithmic parameters
    //      
 
    // Storage for QR factorization of the least squares system.
    std::vector<ScalarType> alpha_, rho_, rho_old_;
    std::vector<MagnitudeType> tau_, cs_, theta_;
    
    // 
    // Current solver state
    //
    // initialized_ specifies that the basis vectors have been initialized and the iterate() routine
    // is capable of running; _initialize is controlled  by the initialize() member method
    // For the implications of the state of initialized_, please see documentation for initialize()
    bool initialized_;
    
    // stateStorageInitialized_ specifies that the state storage has be initialized to the current
    // blockSize_ and numBlocks_.  This initialization may be postponed if the linear problem was
    // generated without the right-hand side or solution vectors.
    bool stateStorageInitialized_;
    
     // Current subspace dimension, and number of iterations performed.
    int iter_;
    
    // 
    // State Storage
    //
    Teuchos::RCP<MV> R_;
    Teuchos::RCP<MV> W_;
    Teuchos::RCP<MV> U_, AU_;
    Teuchos::RCP<MV> Rtilde_;
    Teuchos::RCP<MV> D_;
    Teuchos::RCP<MV> V_;
    Teuchos::RCP<MV> solnUpdate_;
  };
  
  
  //
  // Implementation
  //
  
  // Constructor.
  template <class ScalarType, class MV, class OP, class DM>
  TFQMRIter<ScalarType,MV,OP,DM>::TFQMRIter(const Teuchos::RCP<LinearProblem<ScalarType,MV,OP,DM> > &problem,
           const Teuchos::RCP<OutputManager<ScalarType> > &printer,
           const Teuchos::RCP<StatusTest<ScalarType,MV,OP,DM> > &tester,
           Teuchos::ParameterList &/* params */ 
           ) : 
    lp_(problem), 
    om_(printer),
    stest_(tester),
    alpha_(1),
    rho_(1),
    rho_old_(1),
    tau_(1),
    cs_(1),
    theta_(1),
    initialized_(false),
    stateStorageInitialized_(false),
    iter_(0)
  { 
  }
 
  // Compute native residual from TFQMR recurrence.
  template <class ScalarType, class MV, class OP, class DM>
  Teuchos::RCP<const MV> 
  TFQMRIter<ScalarType,MV,OP,DM>::getNativeResiduals( std::vector<MagnitudeType> *normvec ) const 
  {
    MagnitudeType one = Teuchos::ScalarTraits<MagnitudeType>::one();
    if (normvec)
      (*normvec)[0] = Teuchos::ScalarTraits<MagnitudeType>::squareroot( 2*iter_ + one )*tau_[0];
 
    return Teuchos::null;
  }
  
 
  // Setup the state storage.
  template <class ScalarType, class MV, class OP, class DM>
  void TFQMRIter<ScalarType,MV,OP,DM>::setStateSize ()
  {
    if (!stateStorageInitialized_) {
 
      // Check if there is any multivector to clone from.
      Teuchos::RCP<const MV> lhsMV = lp_->getLHS();
      Teuchos::RCP<const MV> rhsMV = lp_->getRHS();
      if (lhsMV == Teuchos::null && rhsMV == Teuchos::null) {
        stateStorageInitialized_ = false;
        return;
      }
      else {
 
        // Initialize the state storage
        // If the subspace has not be initialized before, generate it using the LHS or RHS from lp_.
        if (R_ == Teuchos::null) {
          // Get the multivector that is not null.
          Teuchos::RCP<const MV> tmp = ( (rhsMV!=Teuchos::null)? rhsMV: lhsMV );
          TEUCHOS_TEST_FOR_EXCEPTION(tmp == Teuchos::null,std::invalid_argument,
                             "Belos::TFQMRIter::setStateSize(): linear problem does not specify multivectors to clone from.");
          R_ = MVT::Clone( *tmp, 1 );
    D_ = MVT::Clone( *tmp, 1 );
          V_ = MVT::Clone( *tmp, 1 );
    solnUpdate_ = MVT::Clone( *tmp, 1 );
        }
 
        // State storage has now been initialized.
        stateStorageInitialized_ = true;
      }
    }
  }
 
  // Initialize this iteration object
  template <class ScalarType, class MV, class OP, class DM>
  void TFQMRIter<ScalarType,MV,OP,DM>::initializeTFQMR(const TFQMRIterState<ScalarType,MV> & newstate)
  {
    // Initialize the state storage if it isn't already.
    if (!stateStorageInitialized_)
      setStateSize();
 
    TEUCHOS_TEST_FOR_EXCEPTION(!stateStorageInitialized_,std::invalid_argument,
                       "Belos::TFQMRIter::initialize(): Cannot initialize state storage!");
 
    // NOTE:  In TFQMRIter R_, the initial residual, is required!!!
    //
    std::string errstr("Belos::TFQMRIter::initialize(): Specified multivectors must have a consistent length and width.");
 
    // Create convenience variables for zero and one.
    const MagnitudeType MTzero = Teuchos::ScalarTraits<MagnitudeType>::zero();
 
    if (newstate.R != Teuchos::null) {
 
      TEUCHOS_TEST_FOR_EXCEPTION( MVT::GetGlobalLength(*newstate.R) != MVT::GetGlobalLength(*R_),
                          std::invalid_argument, errstr );
      TEUCHOS_TEST_FOR_EXCEPTION( MVT::GetNumberVecs(*newstate.R) != 1,
                          std::invalid_argument, errstr );
 
      // Copy basis vectors from newstate into V
      if (newstate.R != R_) {
        // copy over the initial residual (unpreconditioned).
        MVT::Assign( *newstate.R, *R_ );
      }
 
      // Compute initial vectors
      // Initially, they are set to the preconditioned residuals
      //
      W_ = MVT::CloneCopy( *R_ );
      U_ = MVT::CloneCopy( *R_ );
      Rtilde_ = MVT::CloneCopy( *R_ );
      MVT::MvInit( *D_ );
      MVT::MvInit( *solnUpdate_ );
      // Multiply the current residual by Op and store in V_
      //       V_ = Op * R_ 
      //
      lp_->apply( *U_, *V_ );
      AU_ = MVT::CloneCopy( *V_ ); 
      //
      // Compute initial scalars: theta, eta, tau, rho_old
      //
      theta_[0] = MTzero;
      MVT::MvNorm( *R_, tau_ );                         // tau = ||r_0||
      MVT::MvDot( *R_, *Rtilde_, rho_old_ );            // rho = (r_tilde, r0)
    }
    else {
 
      TEUCHOS_TEST_FOR_EXCEPTION(newstate.R == Teuchos::null,std::invalid_argument,
                         "Belos::TFQMRIter::initialize(): TFQMRIterState does not have initial residual.");
    }
 
    // The solver is initialized
    initialized_ = true;
  }
 
 
  // Iterate until the status test informs us we should stop.
  template <class ScalarType, class MV, class OP, class DM>
  void TFQMRIter<ScalarType,MV,OP,DM>::iterate() 
  {
    //
    // Allocate/initialize data structures
    //
    if (initialized_ == false) {
      initialize();
    }
 
    // Create convenience variables for zero and one.
    const ScalarType STone = Teuchos::ScalarTraits<ScalarType>::one();
    const MagnitudeType MTone = Teuchos::ScalarTraits<MagnitudeType>::one();
    const MagnitudeType MTzero = Teuchos::ScalarTraits<MagnitudeType>::zero();
    const ScalarType STzero = Teuchos::ScalarTraits<ScalarType>::zero();
    ScalarType eta = STzero, beta = STzero;
    //
    //  Start executable statements. 
    //
    // Get the current solution vector.
    Teuchos::RCP<MV> cur_soln_vec = lp_->getCurrLHSVec();
 
    // Check that the current solution vector only has one column.
    TEUCHOS_TEST_FOR_EXCEPTION( MVT::GetNumberVecs(*cur_soln_vec) != 1, TFQMRIterateFailure,
                        "Belos::TFQMRIter::iterate(): current linear system has more than one vector!" );
 
 
    // Iterate until the status test tells us to stop.
    //
    while (stest_->checkStatus(this) != Passed) {
 
      for (int iIter=0; iIter<2; iIter++)
      {
        //
        //--------------------------------------------------------
        // Compute the new alpha if we need to
        //--------------------------------------------------------
        //
        if (iIter == 0) {
      MVT::MvDot( *V_, *Rtilde_, alpha_ );      //   alpha = rho / (r_tilde, v) 
    alpha_[0] = rho_old_[0]/alpha_[0];
        }
        //
        //--------------------------------------------------------
        // Update w.
        //   w = w - alpha*Au
        //--------------------------------------------------------
        //
        MVT::MvAddMv( STone, *W_, -alpha_[0], *AU_, *W_ );
        //
        //--------------------------------------------------------
        // Update d.
        //   d = u + (theta^2/alpha)eta*d
        //--------------------------------------------------------
        //
        MVT::MvAddMv( STone, *U_, (theta_[0]*theta_[0]/alpha_[0])*eta, *D_, *D_ );
        //
        //--------------------------------------------------------
        // Update u if we need to.
        //   u = u - alpha*v
        //   
        // Note: This is usually computed with alpha (above), but we're trying be memory efficient.
        //--------------------------------------------------------
        //
        if (iIter == 0) {
          // Compute new U.
      MVT::MvAddMv( STone, *U_, -alpha_[0], *V_, *U_ );
 
      // Update Au for the next iteration.
    lp_->apply( *U_, *AU_ );                       
        }
        //
        //--------------------------------------------------------
        // Compute the new theta, c, eta, tau; i.e. the update to the least squares solution.
        //--------------------------------------------------------
        //
        MVT::MvNorm( *W_, theta_ );     // theta = ||w|| / tau
        theta_[0] /= tau_[0];
        // cs = 1.0 / sqrt(1.0 + theta^2)
        cs_[0] = MTone / Teuchos::ScalarTraits<MagnitudeType>::squareroot(MTone + theta_[0]*theta_[0]);  
        tau_[0] *= theta_[0]*cs_[0];     // tau = tau * theta * cs
        eta = cs_[0]*cs_[0]*alpha_[0];     // eta = cs^2 * alpha
        //
        //--------------------------------------------------------
        // Update the solution.
        // Don't update the linear problem object, may incur additional preconditioner application.
        //--------------------------------------------------------
        //
        MVT::MvAddMv( STone, *solnUpdate_, eta, *D_, *solnUpdate_ );
        //
        //--------------------------------------------------------
        // Check for breakdown before continuing.
        //--------------------------------------------------------
        if ( tau_[0] == MTzero ) {
          break;
        } 
        //
        if (iIter == 1) {
      //
    //--------------------------------------------------------
    // Compute the new rho, beta if we need to.
    //--------------------------------------------------------
    //
      MVT::MvDot( *W_, *Rtilde_, rho_ );                // rho = (r_tilde, w)
    beta = rho_[0]/rho_old_[0];                       // beta = rho / rho_old
    rho_old_[0] = rho_[0];                            // rho_old = rho
    //
    //--------------------------------------------------------
    // Update u, v, and Au if we need to.
    // Note: We are updating v in two stages to be memory efficient
    //--------------------------------------------------------
    //
    MVT::MvAddMv( STone, *W_, beta, *U_, *U_ );       // u = w + beta*u
  
    // First stage of v update.
    MVT::MvAddMv( STone, *AU_, beta, *V_, *V_ );      // v = Au + beta*v 
  
    // Update Au.
    lp_->apply( *U_, *AU_ );                          // Au = A*u
  
    // Second stage of v update.
    MVT::MvAddMv( STone, *AU_, beta, *V_, *V_ );      // v = Au + beta*v
        }
 
      }
 
      // Increment the iteration
      iter_++;
      
    } // end while (sTest_->checkStatus(this) != Passed)
  } 
 
} // namespace Belos
//
#endif // BELOS_TFQMR_ITER_HPP
//
// End of file BelosTFQMRIter.hpp