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solver_cg.hh
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/**
* @file solver_cg.hh
*
* @author Till Junge <till.junge@epfl.ch>
*
* @date 20 Dec 2017
*
* @brief class for a simple implementation of a conjugate gradient
* solver. This follows algorithm 5.2 in Nocedal's Numerical
* Optimization (p 112)
*
* Copyright © 2017 Till Junge
*
* µSpectre is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation, either version 3, or (at
* your option) any later version.
*
* µSpectre 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
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GNU Emacs; see the file COPYING. If not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
#ifndef SOLVER_CG_H
#define SOLVER_CG_H
#include "solver/solver_base.hh"
#include "common/field.hh"
#include <functional>
namespace muSpectre {
/**
* implements the `muSpectre::SolverBase` interface using a
* conjugate gradient solver. This particular class is useful for
* trouble shooting, as it can be made very verbose, but for
* production runs, it is probably better to use
* `muSpectre::SolverCGEigen`.
*/
template <Dim_t DimS, Dim_t DimM=DimS>
class SolverCG: public SolverBase<DimS, DimM>
{
public:
using Parent = SolverBase<DimS, DimM>; //!< base class
//! Input vector for solvers
using SolvVectorIn = typename Parent::SolvVectorIn;
//! Input vector for solvers
using SolvVectorInC = typename Parent::SolvVectorInC;
//! Output vector for solvers
using SolvVectorOut = typename Parent::SolvVectorOut;
using Sys_t = typename Parent::Sys_t; //!< cell type
using Ccoord = typename Parent::Ccoord; //!< cell coordinates type
//! kind of tangent that is required
using Tg_req_t = typename Parent::TangentRequirement;
//! cg only needs to handle fields that look like strain and stress
using Field_t = TensorField<
typename Parent::Collection_t, Real, secondOrder, DimM>;
//! conjugate gradient needs directional stiffness
constexpr static Tg_req_t tangent_requirement{Tg_req_t::NeedEffect};
//! Default constructor
SolverCG() = delete;
//! Constructor with domain resolutions, etc,
SolverCG(Sys_t& sys, Real tol, Uint maxiter=0, bool verbose =false);
//! Copy constructor
SolverCG(const SolverCG &other) = delete;
//! Move constructor
SolverCG(SolverCG &&other) = default;
//! Destructor
virtual ~SolverCG() = default;
//! Copy assignment operator
SolverCG& operator=(const SolverCG &other) = delete;
//! Move assignment operator
SolverCG& operator=(SolverCG &&other) = default;
bool has_converged() const override final {return this->converged;}
//! actual solver
void solve(const Field_t & rhs,
Field_t & x);
// this simplistic implementation has no initialisation phase so the default is ok
SolvVectorOut solve(const SolvVectorInC rhs, SolvVectorIn x_0) override final;
std::string name() const override final {return "CG";}
protected:
//! returns `muSpectre::Tg_req_t::NeedEffect`
Tg_req_t get_tangent_req() const override final;
Field_t & r_k; //!< residual
Field_t & p_k; //!< search direction
Field_t & Ap_k; //!< effect of tangent on search direction
bool converged{false}; //!< whether the solver has converged
private:
};
} // muSpectre
#endif /* SOLVER_CG_H */

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