implicit_problem_wrapper.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 <type_traits>
#include <utility>  // IWYU pragma: keep
 
#include <Eigen/LU>
 
#include "num_collect/base/concepts/eigen_solver_of.h"
#include "num_collect/ode/concepts/mass_problem.h"
#include "num_collect/ode/concepts/multi_variate_problem.h"
#include "num_collect/ode/concepts/single_variate_problem.h"
#include "num_collect/ode/evaluation_type.h"
 
namespace num_collect::ode {
 
template <concepts::single_variate_problem Problem>
    requires concepts::mass_problem<Problem>
class single_variate_implicit_problem_wrapper {
public:
    using variable_type = typename Problem::variable_type;
 
    using scalar_type = typename Problem::scalar_type;
 
    static constexpr auto allowed_evaluations =
        num_collect::ode::evaluation_type{.diff_coeff = true};
 
    explicit single_variate_implicit_problem_wrapper(Problem problem)
        : problem_(std::move(problem)) {}
 
    void evaluate_on(const scalar_type& time, const variable_type& variable,
        evaluation_type /*evaluations*/) {
        problem_.evaluate_on(
            time, variable, evaluation_type{.diff_coeff = true, .mass = true});
        diff_coeff_ = problem_.diff_coeff() / problem_.mass();
    }
 
    [[nodiscard]] auto diff_coeff() const noexcept -> const variable_type& {
        return diff_coeff_;
    }
 
private:
    Problem problem_;
 
    variable_type diff_coeff_{};
};
 
template <concepts::multi_variate_problem Problem,
    base::concepts::eigen_solver_of<typename Problem::mass_type,
        typename Problem::variable_type>
        LinearEquationSolver = Eigen::PartialPivLU<typename Problem::mass_type>>
    requires concepts::mass_problem<Problem>
class multi_variate_implicit_problem_wrapper {
public:
    using variable_type = typename Problem::variable_type;
 
    using scalar_type = typename Problem::scalar_type;
 
    static constexpr auto allowed_evaluations =
        num_collect::ode::evaluation_type{.diff_coeff = true};
 
    explicit multi_variate_implicit_problem_wrapper(Problem problem)
        : problem_(std::move(problem)) {}
 
    void evaluate_on(const scalar_type& time, const variable_type& variable,
        evaluation_type /*evaluations*/) {
        problem_.evaluate_on(
            time, variable, evaluation_type{.diff_coeff = true, .mass = true});
        solver_.compute(problem_.mass());
        diff_coeff_ = solver_.solve(problem_.diff_coeff());
    }
 
    [[nodiscard]] auto diff_coeff() const noexcept -> const variable_type& {
        return diff_coeff_;
    }
 
private:
    Problem problem_;
 
    variable_type diff_coeff_{};
 
    LinearEquationSolver solver_{};
};
 
template <concepts::single_variate_problem Problem>
    requires concepts::mass_problem<Problem>
[[nodiscard]] auto wrap_implicit_problem(Problem&& problem)
    -> single_variate_implicit_problem_wrapper<std::decay_t<Problem>> {
    return single_variate_implicit_problem_wrapper<std::decay_t<Problem>>(
        std::forward<Problem>(problem));
}
 
#ifndef NUM_COLLECT_DOCUMENTATION
// This function causes errors in Doxygen.
 
template <concepts::multi_variate_problem Problem>
    requires concepts::mass_problem<Problem>
[[nodiscard]] auto wrap_implicit_problem(Problem&& problem)
    -> multi_variate_implicit_problem_wrapper<std::decay_t<Problem>> {
    return multi_variate_implicit_problem_wrapper<std::decay_t<Problem>>(
        std::forward<Problem>(problem));
}
#endif
 
}  // namespace num_collect::ode