cubic_root_test_function.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
 
namespace num_prob_collect::roots {

class cubic_root_test_function {
public:
    using variable_type = double;

    using jacobian_type = double;

    explicit cubic_root_test_function(variable_type target) : target_(target) {}

    void evaluate_on(const variable_type& variable) {
        value_ = variable * variable * variable - target_;
        jacobian_ = 3.0 * variable * variable;  // NOLINT
    }

    [[nodiscard]] auto value() const noexcept -> const variable_type& {
        return value_;
    }

    [[nodiscard]] auto jacobian() const noexcept -> const jacobian_type& {
        return jacobian_;
    }
 
private:
    variable_type target_;

    variable_type value_{};

    jacobian_type jacobian_{};
};
 
}  // namespace num_prob_collect::roots