SparseSymMatProd.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 SPARSE_SYM_MAT_PROD_H
#define SPARSE_SYM_MAT_PROD_H

#include <Eigen/Core>
#include <Eigen/SparseCore>

namespace Spectra {

template <typename Scalar, int Uplo = Eigen::Lower, int Flags = 0, typename StorageIndex = int>
class SparseSymMatProd
{
private:
    typedef Eigen::Index Index;
    typedef Eigen::Matrix<Scalar, Eigen::Dynamic, 1> Vector;
    typedef Eigen::Map<const Vector> MapConstVec;
    typedef Eigen::Map<Vector> MapVec;
    typedef Eigen::SparseMatrix<Scalar, Flags, StorageIndex> SparseMatrix;
    typedef const Eigen::Ref<const SparseMatrix> ConstGenericSparseMatrix;

    ConstGenericSparseMatrix m_mat;

public:
    SparseSymMatProd(ConstGenericSparseMatrix& mat) :
        m_mat(mat)
    {}

    Index rows() const { return m_mat.rows(); }
    Index cols() const { return m_mat.cols(); }

    // y_out = A * x_in
    void perform_op(const Scalar* x_in, Scalar* y_out) const
    {
        MapConstVec x(x_in, m_mat.cols());
        MapVec y(y_out, m_mat.rows());
        y.noalias() = m_mat.template selfadjointView<Uplo>() * x;
    }
};

}  // namespace Spectra

#endif  // SPARSE_SYM_MAT_PROD_H