Eigenpair.hpp

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// 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/Representation/Matrix.hpp"
 
 
namespace GQCP {
 
 
template <typename _EigenvalueScalar, typename _EigenvectorScalar>
class Eigenpair {
public:
    // The scalar type for the representation of an eigenvalue: real or complex.
    using EigenvalueScalar = _EigenvalueScalar;
 
 
    // The scalar type for the representation of one of the coefficients of an eigenvector: real or complex.
    using EigenvectorScalar = _EigenvectorScalar;
 
 
private:
    EigenvalueScalar m_eigenvalue;
    VectorX<EigenvectorScalar> m_eigenvector;
 
 
public:
    // CONSTRUCTORS
 
    Eigenpair(const EigenvalueScalar eigenvalue, const VectorX<EigenvectorScalar>& eigenvector) :
        m_eigenvalue {eigenvalue},
        m_eigenvector {eigenvector} {}
 
    explicit Eigenpair(const size_t dimension = 1) :
        Eigenpair(0.0, VectorX<EigenvectorScalar>::Zero(dimension)) {}
 
 
    // PUBLIC METHODS
 
    EigenvalueScalar eigenvalue() const { return this->m_eigenvalue; };
 
    const VectorX<EigenvectorScalar>& eigenvector() const { return this->m_eigenvector; };
 
    bool isEqualTo(const Eigenpair& other, const double tolerance = 1.0e-08) const {
 
        if (this->eigenvector().size() != other.eigenvector().size()) {
            throw std::invalid_argument("Eigenpair::isEqualTo(Eigenpair, double): Can't compare eigenpairs with eigenvectors of different dimension.");
        }
 
        if (std::abs(this->eigenvalue() - other.eigenvalue()) < tolerance) {
            if ((this->eigenvector()).isEqualEigenvectorAs(other.eigenvector(), tolerance)) {
                return true;
            }
        }
 
        return false;
    }
};
 
 
}  // namespace GQCP