reverse_cuthill_mckee_ordering.h

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/*
 * Copyright 2023 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 <Eigen/Core>
#include <Eigen/SparseCore>
 
#include "num_collect/base/concepts/sparse_matrix.h"
#include "num_collect/linear/cuthill_mckee_ordering.h"
 
namespace num_collect::linear {
 
template <typename StorageIndex>
class reverse_cuthill_mckee_ordering {
public:
    using storage_index_type = StorageIndex;
 
    using permutation_type = Eigen::PermutationMatrix<Eigen::Dynamic,
        Eigen::Dynamic, storage_index_type>;
 
    using PermutationType = permutation_type;
 
    reverse_cuthill_mckee_ordering() = default;
 
    template <base::concepts::sparse_matrix MatrixType>
    void operator()(const MatrixType& matrix, permutation_type& permutation) {
        cuthill_mckee_ordering<storage_index_type>()(matrix, permutation);
        const auto size =
            static_cast<storage_index_type>(permutation.indices().size());
        const storage_index_type size_minus_one = size - 1;
        for (storage_index_type& index : permutation.indices()) {
            index = size_minus_one - index;
        }
    }
 
    template <typename MatrixType, unsigned int Mode>
    void operator()(
        const Eigen::SparseSelfAdjointView<MatrixType, Mode>& matrix,
        permutation_type& permutation) {
        Eigen::SparseMatrix<typename MatrixType::Scalar, Eigen::ColMajor,
            storage_index_type>
            matrix_as_ordinary_matrix = matrix;
        operator()(matrix_as_ordinary_matrix, permutation);
    }
};
 
}  // namespace num_collect::linear