GMRES.h

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// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2011 Gael Guennebaud <gael.guennebaud@inria.fr>
// Copyright (C) 2012, 2014 Kolja Brix <brix@igpm.rwth-aaachen.de>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
#ifndef EIGEN_GMRES_H
#define EIGEN_GMRES_H
 
namespace Eigen {
 
namespace internal {
 
template<typename MatrixType, typename Rhs, typename Dest, typename Preconditioner>
bool gmres(const MatrixType & mat, const Rhs & rhs, Dest & x, const Preconditioner & precond,
    Index &iters, const Index &restart, typename Dest::RealScalar & tol_error) {
 
  using std::sqrt;
  using std::abs;
 
  typedef typename Dest::RealScalar RealScalar;
  typedef typename Dest::Scalar Scalar;
  typedef Matrix < Scalar, Dynamic, 1 > VectorType;
  typedef Matrix < Scalar, Dynamic, Dynamic, ColMajor> FMatrixType;
 
  const RealScalar considerAsZero = (std::numeric_limits<RealScalar>::min)();
 
  if(rhs.norm() <= considerAsZero) 
  {
    x.setZero();
    tol_error = 0;
    return true;
  }
 
  RealScalar tol = tol_error;
  const Index maxIters = iters;
  iters = 0;
 
  const Index m = mat.rows();
 
  // residual and preconditioned residual
  VectorType p0 = rhs - mat*x;
  VectorType r0 = precond.solve(p0);
 
  const RealScalar r0Norm = r0.norm();
 
  // is initial guess already good enough?
  if(r0Norm == 0)
  {
    tol_error = 0;
    return true;
  }
 
  // storage for Hessenberg matrix and Householder data
  FMatrixType H   = FMatrixType::Zero(m, restart + 1);
  VectorType w    = VectorType::Zero(restart + 1);
  VectorType tau  = VectorType::Zero(restart + 1);
 
  // storage for Jacobi rotations
  std::vector < JacobiRotation < Scalar > > G(restart);
  
  // storage for temporaries
  VectorType t(m), v(m), workspace(m), x_new(m);
 
  // generate first Householder vector
  Ref<VectorType> H0_tail = H.col(0).tail(m - 1);
  RealScalar beta;
  r0.makeHouseholder(H0_tail, tau.coeffRef(0), beta);
  w(0) = Scalar(beta);
  
  for (Index k = 1; k <= restart; ++k)
  {
    ++iters;
 
    v = VectorType::Unit(m, k - 1);
 
    // apply Householder reflections H_{1} ... H_{k-1} to v
    // TODO: use a HouseholderSequence
    for (Index i = k - 1; i >= 0; --i) {
      v.tail(m - i).applyHouseholderOnTheLeft(H.col(i).tail(m - i - 1), tau.coeffRef(i), workspace.data());
    }
 
    // apply matrix M to v:  v = mat * v;
    t.noalias() = mat * v;
    v = precond.solve(t);
 
    // apply Householder reflections H_{k-1} ... H_{1} to v
    // TODO: use a HouseholderSequence
    for (Index i = 0; i < k; ++i) {
      v.tail(m - i).applyHouseholderOnTheLeft(H.col(i).tail(m - i - 1), tau.coeffRef(i), workspace.data());
    }
 
    if (v.tail(m - k).norm() != 0.0)
    {
      if (k <= restart)
      {
        // generate new Householder vector
        Ref<VectorType> Hk_tail = H.col(k).tail(m - k - 1);
        v.tail(m - k).makeHouseholder(Hk_tail, tau.coeffRef(k), beta);
 
        // apply Householder reflection H_{k} to v
        v.tail(m - k).applyHouseholderOnTheLeft(Hk_tail, tau.coeffRef(k), workspace.data());
      }
    }
 
    if (k > 1)
    {
      for (Index i = 0; i < k - 1; ++i)
      {
        // apply old Givens rotations to v
        v.applyOnTheLeft(i, i + 1, G[i].adjoint());
      }
    }
 
    if (k<m && v(k) != (Scalar) 0)
    {
      // determine next Givens rotation
      G[k - 1].makeGivens(v(k - 1), v(k));
 
      // apply Givens rotation to v and w
      v.applyOnTheLeft(k - 1, k, G[k - 1].adjoint());
      w.applyOnTheLeft(k - 1, k, G[k - 1].adjoint());
    }
 
    // insert coefficients into upper matrix triangle
    H.col(k-1).head(k) = v.head(k);
 
    tol_error = abs(w(k)) / r0Norm;
    bool stop = (k==m || tol_error < tol || iters == maxIters);
 
    if (stop || k == restart)
    {
      // solve upper triangular system
      Ref<VectorType> y = w.head(k);
      H.topLeftCorner(k, k).template triangularView <Upper>().solveInPlace(y);
 
      // use Horner-like scheme to calculate solution vector
      x_new.setZero();
      for (Index i = k - 1; i >= 0; --i)
      {
        x_new(i) += y(i);
        // apply Householder reflection H_{i} to x_new
        x_new.tail(m - i).applyHouseholderOnTheLeft(H.col(i).tail(m - i - 1), tau.coeffRef(i), workspace.data());
      }
 
      x += x_new;
 
      if(stop)
      {
        return true;
      }
      else
      {
        k=0;
 
        // reset data for restart
        p0.noalias() = rhs - mat*x;
        r0 = precond.solve(p0);
 
        // clear Hessenberg matrix and Householder data
        H.setZero();
        w.setZero();
        tau.setZero();
 
        // generate first Householder vector
        r0.makeHouseholder(H0_tail, tau.coeffRef(0), beta);
        w(0) = Scalar(beta);
      }
    }
  }
 
  return false;
 
}
 
}
 
template< typename _MatrixType,
          typename _Preconditioner = DiagonalPreconditioner<typename _MatrixType::Scalar> >
class GMRES;
 
namespace internal {
 
template< typename _MatrixType, typename _Preconditioner>
struct traits<GMRES<_MatrixType,_Preconditioner> >
{
  typedef _MatrixType MatrixType;
  typedef _Preconditioner Preconditioner;
};
 
}
 
template< typename _MatrixType, typename _Preconditioner>
class GMRES : public IterativeSolverBase<GMRES<_MatrixType,_Preconditioner> >
{
  typedef IterativeSolverBase<GMRES> Base;
  using Base::matrix;
  using Base::m_error;
  using Base::m_iterations;
  using Base::m_info;
  using Base::m_isInitialized;
 
private:
  Index m_restart;
 
public:
  using Base::_solve_impl;
  typedef _MatrixType MatrixType;
  typedef typename MatrixType::Scalar Scalar;
  typedef typename MatrixType::RealScalar RealScalar;
  typedef _Preconditioner Preconditioner;
 
public:
 
  GMRES() : Base(), m_restart(30) {}
 
  template<typename MatrixDerived>
  explicit GMRES(const EigenBase<MatrixDerived>& A) : Base(A.derived()), m_restart(30) {}
 
  ~GMRES() {}
 
  Index get_restart() { return m_restart; }
 
  void set_restart(const Index restart) { m_restart=restart; }
 
  template<typename Rhs,typename Dest>
  void _solve_vector_with_guess_impl(const Rhs& b, Dest& x) const
  {
    m_iterations = Base::maxIterations();
    m_error = Base::m_tolerance;
    bool ret = internal::gmres(matrix(), b, x, Base::m_preconditioner, m_iterations, m_restart, m_error);
    m_info = (!ret) ? NumericalIssue
          : m_error <= Base::m_tolerance ? Success
          : NoConvergence;
  }
 
protected:
 
};
 
} // end namespace Eigen
 
#endif // EIGEN_GMRES_H