euclidean_distance_function.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"
#include "num_collect/base/concepts/real_scalar_dense_vector.h"
#include "num_collect/base/norm.h"
 
namespace num_collect::rbf::distance_functions {
 
template <typename Variable>
class euclidean_distance_function;
 
template <base::concepts::real_scalar_dense_vector Variable>
class euclidean_distance_function<Variable> {
public:
    using variable_type = Variable;
 
    using value_type = typename Variable::Scalar;
 
    [[nodiscard]] auto operator()(const variable_type& var1,
        const variable_type& var2) const noexcept -> value_type {
        return norm(var1 - var2);
    }
};
 
template <base::concepts::real_scalar Variable>
class euclidean_distance_function<Variable> {
public:
    using variable_type = Variable;
 
    using value_type = Variable;
 
    [[nodiscard]] auto operator()(const variable_type& var1,
        const variable_type& var2) const noexcept -> value_type {
        using std::abs;
        return abs(var1 - var2);
    }
};
 
}  // namespace num_collect::rbf::distance_functions