multi_quadric_rbf.h

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/*
 * 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.
 */
#pragma once
 
#include <cmath>
 
#include "num_collect/base/concepts/real_scalar.h"
 
namespace num_collect::rbf::rbfs {

template <base::concepts::real_scalar Scalar>
class multi_quadric_rbf {
public:
    using scalar_type = Scalar;

    [[nodiscard]] auto operator()(
        const scalar_type& distance_rate) const noexcept -> scalar_type {
        using std::sqrt;
        return sqrt(
            static_cast<scalar_type>(1) + distance_rate * distance_rate);
    }
};
 
}  // namespace num_collect::rbf::rbfs