avf_integrand.h

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/*
 * Copyright 2021 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 "num_collect/constants/one.h"  // IWYU pragma: keep
#include "num_collect/ode/concepts/problem.h"
#include "num_collect/ode/evaluation_type.h"
 
namespace num_collect::ode::avf::impl {
 
template <concepts::problem Problem>
class avf_integrand {
public:
    using problem_type = Problem;
 
    using variable_type = typename problem_type::variable_type;
 
    using scalar_type = typename problem_type::scalar_type;
 
    static_assert(!problem_type::allowed_evaluations.mass,
        "Mass matrix is not supported.");
 
    explicit avf_integrand(const problem_type& problem = problem_type())
        : problem_(problem) {}
 
    [[nodiscard]] auto operator()(scalar_type rate) const -> variable_type {
        problem_.evaluate_on(time_,
            (constants::one<scalar_type> - rate) * prev_var_ + rate * next_var_,
            evaluation_type{.diff_coeff = true});
        return problem_.diff_coeff();
    }
 
    [[nodiscard]] auto problem() -> problem_type& { return problem_; }
 
    [[nodiscard]] auto problem() const -> const problem_type& {
        return problem_;
    }
 
    void time(scalar_type val) { time_ = val; }
 
    void prev_var(const variable_type& var) { prev_var_ = var; }
 
    void next_var(const variable_type& var) { next_var_ = var; }
 
private:
    mutable problem_type problem_;
 
    scalar_type time_{};
 
    variable_type prev_var_{};
 
    variable_type next_var_{};
};
 
}  // namespace num_collect::ode::avf::impl