eigen_solvers.h

/*
 * Copyright 2025 Adobe. All rights reserved.
 * This file is licensed to you 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 REPRESENTATIONS
 * 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/Sparse>
 
namespace lagrange::solver {

enum class Status { Successful, NotComputed, NotConverging, NumericalIssue };

template <typename Scalar>
struct EigenResult
{
    Eigen::Matrix<Scalar, Eigen::Dynamic, 1> eigenvalues;

    Eigen::Matrix<Scalar, Eigen::Dynamic, Eigen::Dynamic> eigenvectors;

    size_t num_converged = 0;

    Status info = Status::NotComputed;

    bool is_successful() const { return info == Status::Successful; }
};

template <typename Scalar>
EigenResult<Scalar> selfadjoint_eigen_largest(const Eigen::SparseMatrix<Scalar>& A, size_t k);

template <typename Scalar>
EigenResult<Scalar> selfadjoint_eigen_smallest(const Eigen::SparseMatrix<Scalar>& A, size_t k);

template <typename Scalar>
EigenResult<Scalar> generalized_selfadjoint_eigen_largest(
    const Eigen::SparseMatrix<Scalar>& A,
    const Eigen::SparseMatrix<Scalar>& M,
    size_t k);

template <typename Scalar>
EigenResult<Scalar> generalized_selfadjoint_eigen_smallest(
    const Eigen::SparseMatrix<Scalar>& A,
    const Eigen::SparseMatrix<Scalar>& M,
    size_t k);
 
} // namespace lagrange::solver