SubspaceMatrixCalculation.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/Algorithm/Step.hpp"
#include "Mathematical/Optimization/Eigenproblem/EigenproblemEnvironment.hpp"
 
#include <type_traits>
 
 
namespace GQCP {
 
 
class SubspaceMatrixCalculation:
    public Step<EigenproblemEnvironment<double>> {
 
public:
    /*
     *  PUBLIC OVERRIDDEN METHODS
     */
 
    std::string description() const override {
        return "Calculate the subspace matrix, i.e. the projection of the matrix A onto the subspace spanned by the vectors in V.";
    }
 
 
    void execute(EigenproblemEnvironment<double>& environment) override {
 
        const auto& V = environment.V;    // the subspace of guess vectors
        const auto& VA = environment.VA;  // VA = A * V (implicitly calculated through the matrix-vector product)
 
        environment.S = V.transpose() * VA;  // the "subspace matrix": the projection of the matrix A onto the subspace spanned by the vectors in V
    }
};
 
 
}  // namespace GQCP