SymEigsShiftSolver.h

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// Copyright (C) 2016-2019 Yixuan Qiu <yixuan.qiu@cos.name>
//
// 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 https://mozilla.org/MPL/2.0/.

#ifndef SYM_EIGS_SHIFT_SOLVER_H
#define SYM_EIGS_SHIFT_SOLVER_H

#include <Eigen/Core>

#include "SymEigsBase.h"
#include "Util/SelectionRule.h"
#include "MatOp/DenseSymShiftSolve.h"

namespace Spectra {

template <typename Scalar = double,
          int SelectionRule = LARGEST_MAGN,
          typename OpType = DenseSymShiftSolve<double> >
class SymEigsShiftSolver : public SymEigsBase<Scalar, SelectionRule, OpType, IdentityBOp>
{
private:
    typedef Eigen::Index Index;
    typedef Eigen::Array<Scalar, Eigen::Dynamic, 1> Array;

    const Scalar m_sigma;

    // First transform back the Ritz values, and then sort
    void sort_ritzpair(int sort_rule)
    {
        Array m_ritz_val_org = Scalar(1.0) / this->m_ritz_val.head(this->m_nev).array() + m_sigma;
        this->m_ritz_val.head(this->m_nev) = m_ritz_val_org;
        SymEigsBase<Scalar, SelectionRule, OpType, IdentityBOp>::sort_ritzpair(sort_rule);
    }

public:
    SymEigsShiftSolver(OpType* op, Index nev, Index ncv, Scalar sigma) :
        SymEigsBase<Scalar, SelectionRule, OpType, IdentityBOp>(op, NULL, nev, ncv),
        m_sigma(sigma)
    {
        this->m_op->set_shift(m_sigma);
    }
};

}  // namespace Spectra

#endif  // SYM_EIGS_SHIFT_SOLVER_H