GeneralizedEigenproblemEnvironment.hpp

Go to the documentation of this file.

// This file is part of GQCG-GQCP.
//
// Copyright (C) 2017-2020  the GQCG developers
//
// GQCG-GQCP is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// GQCG-GQCP 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 Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with GQCG-GQCP.  If not, see <http://www.gnu.org/licenses/>.
 
#pragma once
 
 
#include "Mathematical/Optimization/Eigenproblem/Eigenpair.hpp"
#include "Mathematical/Representation/Matrix.hpp"
#include "Mathematical/Representation/SquareMatrix.hpp"
 
 
namespace GQCP {
 
 
template <typename _Scalar>
class GeneralizedEigenproblemEnvironment {
public:
    // The scalar type of the matrix elements: real or complex.
    using Scalar = _Scalar;
 
 
public:
    // The matrix whose eigenvalue problem should be solved.
    SquareMatrix<Scalar> A;
 
    // The transformation matrix needed to solve the generalized eigenvalue problem.
    SquareMatrix<Scalar> S;
 
    // The eigenvalues of the matrix A.
    VectorX<double> eigenvalues;
 
    // The eigenvectors of the matrix A.
    MatrixX<Scalar> eigenvectors;
 
 
public:
    /*
     *  MARK: Constructors
     */
 
    GeneralizedEigenproblemEnvironment(const SquareMatrix<Scalar>& A, const SquareMatrix<Scalar>& S) :
        A {A},
        S {S} {}
 
 
    /*
     *  MARK: Named constructors
     */
 
    static GeneralizedEigenproblemEnvironment Dense(const SquareMatrix<Scalar>& A, const SquareMatrix<Scalar>& S) { return GeneralizedEigenproblemEnvironment(A, S); }
 
 
    /*
     *  MARK: Access
     */
 
    std::vector<Eigenpair<double, Scalar>> eigenpairs(const size_t number_of_requested_eigenpairs = 1) const {
 
        if (number_of_requested_eigenpairs > this->eigenvectors.cols()) {
            throw std::invalid_argument("GeneralEigenproblemEnvironment::eigenpairs(const size_t): You cannot retrieve that many eigenpairs.");
        }
 
        std::vector<Eigenpair<double, Scalar>> eigenpairs {};
        eigenpairs.reserve(number_of_requested_eigenpairs);
 
        for (size_t i = 0; i < number_of_requested_eigenpairs; i++) {
            const auto& eigenvalue = this->eigenvalues(i);
            const auto& eigenvector = this->eigenvectors.col(i);
 
            eigenpairs.emplace_back(eigenvalue, eigenvector);
        }
 
        return eigenpairs;
    }
};
 
 
}  // namespace GQCP