/*

 * Copyright 2024 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.

 */

/*!

 * \file

 * \brief Definition of gaussian_rbf class.

 */

#pragma once

#include <cmath>

#include "num_collect/base/concepts/real_scalar.h"

namespace num_collect::rbf::rbfs {

/*!

 * \brief Class of Gaussian RBF \cite Fornberg2015.

 *

 * \tparam Scalar Type of scalars.

 */

template <base::concepts::real_scalar Scalar>

class gaussian_rbf {

public:

    //! Type of scalars.

    using scalar_type = Scalar;

    /*!

     * \brief Calculate a function value of RBF.

     *

     * \param[in] distance_rate Rate of distance.

     * \return Value of this RBF.

     */

    [[nodiscard]] auto operator()(

        const scalar_type& distance_rate) const noexcept -> scalar_type {

        using std::exp;

        return exp(-distance_rate * distance_rate);

    }

};

}  // namespace num_collect::rbf::rbfs