T2ErrorCalculation.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 "QCMethod/CC/CCSDEnvironment.hpp"
 
 
namespace GQCP {
 
 
template <typename _Scalar>
class T2ErrorCalculation:
    public Step<CCSDEnvironment<_Scalar>> {
 
public:
    // The scalar type used to represent the T2 amplitudes.
    using Scalar = _Scalar;
 
    // The environment related to this step.
    using Environment = CCSDEnvironment<Scalar>;
 
 
public:
    /*
     *  MARK: Conforming to `Step`
     */
 
    std::string description() const override {
        return "Calculate the current T2 error vector and add it to the environment.";
    }
 
 
    void execute(Environment& environment) override {
 
        // Read the last two T2 amplitudes iterations and calculate the error as their difference.
        const auto second_to_last_it = environment.t2_amplitudes.end() - 2;
        const auto& T2_previous = *second_to_last_it;  // Dereference the iterator.
 
        const auto& T2_current = environment.t2_amplitudes.back();
 
        // Calculate the current T2 error vector and add it to the environment (as a vector).
        const auto t2_error = T2_current - T2_previous;
        environment.t2_amplitude_errors.push_back(t2_error.asImplicitRankFourTensorSlice().asMatrix().pairWiseReduced());
    }
};
 
 
}  // namespace GQCP