// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2011-2014 Gael Guennebaud <gael.guennebaud@inria.fr>
//
// 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_CONJUGATE_GRADIENT_H
#define EIGEN_CONJUGATE_GRADIENT_H
namespace Eigen {
namespace internal {
/** \internal Low-level conjugate gradient algorithm
* \param mat The matrix A
* \param rhs The right hand side vector b
* \param x On input and initial solution, on output the computed solution.
* \param precond A preconditioner being able to efficiently solve for an
* approximation of Ax=b (regardless of b)
* \param iters On input the max number of iteration, on output the number of performed iterations.
* \param tol_error On input the tolerance error, on output an estimation of the relative error.
*/
template<typename MatrixType, typename Rhs, typename Dest, typename Preconditioner>
EIGEN_DONT_INLINE
void conjugate_gradient(const MatrixType& mat, const Rhs& rhs, Dest& x,
const Preconditioner& precond, Index& iters,
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;
RealScalar tol = tol_error;
Index maxIters = iters;
Index n = mat.cols();
VectorType residual = rhs - mat * x; //initial residual
RealScalar rhsNorm2 = rhs.squaredNorm();
if(rhsNorm2 == 0)
{
x.setZero();
iters = 0;
tol_error = 0;
return;
}
RealScalar threshold = tol*tol*rhsNorm2;
RealScalar residualNorm2 = residual.squaredNorm();
if (residualNorm2 < threshold)
{
iters = 0;
tol_error = sqrt(residualNorm2 / rhsNorm2);
return;
}
VectorType p(n);
p = precond.solve(residual); // initial search direction
VectorType z(n), tmp(n);
RealScalar absNew = numext::real(residual.dot(p)); // the square of the absolute value of r scaled by invM
Index i = 0;
while(i < maxIters)
{
tmp.noalias() = mat * p; // the bottleneck of the algorithm
Scalar alpha = absNew / p.dot(tmp); // the amount we travel on dir
x += alpha * p; // update solution
residual -= alpha * tmp; // update residual
residualNorm2 = residual.squaredNorm();
if(residualNorm2 < threshold)
break;
z = precond.solve(residual); // approximately solve for "A z = residual"
RealScalar absOld = absNew;
absNew = numext::real(residual.dot(z)); // update the absolute value of r
RealScalar beta = absNew / absOld; // calculate the Gram-Schmidt value used to create the new search direction
p = z + beta * p; // update search direction
i++;
}
tol_error = sqrt(residualNorm2 / rhsNorm2);
iters = i;
}
}
template< typename _MatrixType, int _UpLo=Lower,
typename _Preconditioner = DiagonalPreconditioner<typename _MatrixType::Scalar> >
class ConjugateGradient;
namespace internal {
template< typename _MatrixType, int _UpLo, typename _Preconditioner>
struct traits<ConjugateGradient<_MatrixType,_UpLo,_Preconditioner> >
{
typedef _MatrixType MatrixType;
typedef _Preconditioner Preconditioner;
};
}
/** \ingroup IterativeLinearSolvers_Module
* \brief A conjugate gradient solver for sparse (or dense) self-adjoint problems
*
* This class allows to solve for A.x = b linear problems using an iterative conjugate gradient algorithm.
* The matrix A must be selfadjoint. The matrix A and the vectors x and b can be either dense or sparse.
*
* \tparam _MatrixType the type of the matrix A, can be a dense or a sparse matrix.
* \tparam _UpLo the triangular part that will be used for the computations. It can be Lower,
* \c Upper, or \c Lower|Upper in which the full matrix entries will be considered.
* Default is \c Lower, best performance is \c Lower|Upper.
* \tparam _Preconditioner the type of the preconditioner. Default is DiagonalPreconditioner
*
* \implsparsesolverconcept
*
* The maximal number of iterations and tolerance value can be controlled via the setMaxIterations()
* and setTolerance() methods. The defaults are the size of the problem for the maximal number of iterations
* and NumTraits<Scalar>::epsilon() for the tolerance.
*
* The tolerance corresponds to the relative residual error: |Ax-b|/|b|
*
* \b Performance: Even though the default value of \c _UpLo is \c Lower, significantly higher performance is
* achieved when using a complete matrix and \b Lower|Upper as the \a _UpLo template parameter. Moreover, in this
* case multi-threading can be exploited if the user code is compiled with OpenMP enabled.
* See \ref TopicMultiThreading for details.
*
* This class can be used as the direct solver classes. Here is a typical usage example:
\code
int n = 10000;
VectorXd x(n), b(n);
SparseMatrix<double> A(n,n);
// fill A and b
ConjugateGradient<SparseMatrix<double>, Lower|Upper> cg;
cg.compute(A);
x = cg.solve(b);
std::cout << "#iterations: " << cg.iterations() << std::endl;
std::cout << "estimated error: " << cg.error() << std::endl;
// update b, and solve again
x = cg.solve(b);
\endcode
*
* By default the iterations start with x=0 as an initial guess of the solution.
* One can control the start using the solveWithGuess() method.
*
* ConjugateGradient can also be used in a matrix-free context, see the following \link MatrixfreeSolverExample example \endlink.
*
* \sa class LeastSquaresConjugateGradient, class SimplicialCholesky, DiagonalPreconditioner, IdentityPreconditioner
*/
template< typename _MatrixType, int _UpLo, typename _Preconditioner>
class ConjugateGradient : public IterativeSolverBase<ConjugateGradient<_MatrixType,_UpLo,_Preconditioner> >
{
typedef IterativeSolverBase<ConjugateGradient> Base;
using Base::matrix;
using Base::m_error;
using Base::m_iterations;
using Base::m_info;
using Base::m_isInitialized;
public:
typedef _MatrixType MatrixType;
typedef typename MatrixType::Scalar Scalar;
typedef typename MatrixType::RealScalar RealScalar;
typedef _Preconditioner Preconditioner;
enum {
UpLo = _UpLo
};
public:
/** Default constructor. */
ConjugateGradient() : Base() {}
/** Initialize the solver with matrix \a A for further \c Ax=b solving.
*
* This constructor is a shortcut for the default constructor followed
* by a call to compute().
*
* \warning this class stores a reference to the matrix A as well as some
* precomputed values that depend on it. Therefore, if \a A is changed
* this class becomes invalid. Call compute() to update it with the new
* matrix A, or modify a copy of A.
*/
template<typename MatrixDerived>
explicit ConjugateGradient(const EigenBase<MatrixDerived>& A) : Base(A.derived()) {}
~ConjugateGradient() {}
/** \internal */
template<typename Rhs,typename Dest>
void _solve_with_guess_impl(const Rhs& b, Dest& x) const
{
typedef typename Base::MatrixWrapper MatrixWrapper;
typedef typename Base::ActualMatrixType ActualMatrixType;
enum {
TransposeInput = (!MatrixWrapper::MatrixFree)
&& (UpLo==(Lower|Upper))
&& (!MatrixType::IsRowMajor)
&& (!NumTraits<Scalar>::IsComplex)
};
typedef typename internal::conditional<TransposeInput,Transpose<const ActualMatrixType>, ActualMatrixType const&>::type RowMajorWrapper;
EIGEN_STATIC_ASSERT(EIGEN_IMPLIES(MatrixWrapper::MatrixFree,UpLo==(Lower|Upper)),MATRIX_FREE_CONJUGATE_GRADIENT_IS_COMPATIBLE_WITH_UPPER_UNION_LOWER_MODE_ONLY);
typedef typename internal::conditional<UpLo==(Lower|Upper),
RowMajorWrapper,
typename MatrixWrapper::template ConstSelfAdjointViewReturnType<UpLo>::Type
>::type SelfAdjointWrapper;
m_iterations = Base::maxIterations();
m_error = Base::m_tolerance;
for(Index j=0; j<b.cols(); ++j)
{
m_iterations = Base::maxIterations();
m_error = Base::m_tolerance;
typename Dest::ColXpr xj(x,j);
RowMajorWrapper row_mat(matrix());
internal::conjugate_gradient(SelfAdjointWrapper(row_mat), b.col(j), xj, Base::m_preconditioner, m_iterations, m_error);
}
m_isInitialized = true;
m_info = m_error <= Base::m_tolerance ? Success : NoConvergence;
}
/** \internal */
using Base::_solve_impl;
template<typename Rhs,typename Dest>
void _solve_impl(const MatrixBase<Rhs>& b, Dest& x) const
{
x.setZero();
_solve_with_guess_impl(b.derived(),x);
}
protected:
};
} // end namespace Eigen
#endif // EIGEN_CONJUGATE_GRADIENT_H