changing_mass_quadratic_problem.h

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/*
 * Copyright 2023 MusicScience37 (Kenta Kabashima)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#pragma once
 
#include <cmath>
 
#include <Eigen/Core>
 
#include "num_collect/ode/evaluation_type.h"
 
namespace num_prob_collect::ode {
 
class changing_mass_quadratic_problem {
public:
    using variable_type = Eigen::Vector2d;
 
    using scalar_type = double;
 
    using jacobian_type = Eigen::Matrix2d;
 
    using mass_type = Eigen::Matrix2d;
 
    static constexpr auto allowed_evaluations =
        num_collect::ode::evaluation_type{
            .diff_coeff = true, .jacobian = true, .mass = true};
 
    changing_mass_quadratic_problem() {
        jacobian_(1, 0) = 1.0;
        mass_(1, 1) = 1.0;
    }
 
    void evaluate_on(scalar_type /*time*/, const variable_type& variable,
        num_collect::ode::evaluation_type evaluations) {
        const double exp_x = std::exp(variable(1));
        diff_coeff_(0) = exp_x;
        diff_coeff_(1) = variable(0);
        if (evaluations.jacobian) {
            jacobian_(0, 1) = exp_x;
        }
        mass_(0, 0) = exp_x;
    }
 
    [[nodiscard]] auto diff_coeff() const noexcept -> const variable_type& {
        return diff_coeff_;
    }
 
    [[nodiscard]] auto jacobian() const noexcept -> const jacobian_type& {
        return jacobian_;
    }
 
    [[nodiscard]] auto mass() const noexcept -> const mass_type& {
        return mass_;
    }
 
private:
    variable_type diff_coeff_{};
 
    jacobian_type jacobian_{jacobian_type::Zero()};
 
    mass_type mass_{mass_type::Zero()};
};
 
}  // namespace num_prob_collect::ode