chebyshev.hpp

// SPDX-FileCopyrightText: 2025 - 2026 The Ginkgo authors
//
// SPDX-License-Identifier: BSD-3-Clause
 
#ifndef GKO_PUBLIC_CORE_SOLVER_CHEBYSHEV_HPP_
#define GKO_PUBLIC_CORE_SOLVER_CHEBYSHEV_HPP_
 
 
#include <vector>
 
#include <ginkgo/core/base/exception_helpers.hpp>
#include <ginkgo/core/base/lin_op.hpp>
#include <ginkgo/core/base/types.hpp>
#include <ginkgo/core/config/config.hpp>
#include <ginkgo/core/config/registry.hpp>
#include <ginkgo/core/matrix/dense.hpp>
#include <ginkgo/core/matrix/identity.hpp>
#include <ginkgo/core/solver/solver_base.hpp>
#include <ginkgo/core/stop/combined.hpp>
#include <ginkgo/core/stop/criterion.hpp>
#include <ginkgo/core/stop/iteration.hpp>
 
 
namespace gko {
namespace solver {
namespace detail {
 
 
template <typename T>
using coeff_type =
    std::conditional_t<is_complex<T>(), std::complex<double>, double>;
 
 
}
 
template <typename ValueType = default_precision>
class Chebyshev final
    : public LinOp,
      public EnablePreconditionedIterativeSolver<ValueType,
                                                 Chebyshev<ValueType>>,
      public EnableApplyWithInitialGuess<Chebyshev<ValueType>>,
      public Transposable {
    friend class EnableApplyWithInitialGuess<Chebyshev>;
    GKO_ASSERT_SUPPORTED_VALUE_TYPE;
 
public:
    using value_type = ValueType;
    using transposed_type = Chebyshev<ValueType>;
 
    std::unique_ptr<LinOp> transpose() const override;
 
    std::unique_ptr<LinOp> conj_transpose() const override;
 
    bool apply_uses_initial_guess() const override
    {
        return this->get_default_initial_guess() ==
               initial_guess_mode::provided;
    }
 
    Chebyshev& operator=(const Chebyshev&);
 
    Chebyshev& operator=(Chebyshev&&);
 
    Chebyshev(const Chebyshev&);
 
    Chebyshev(Chebyshev&&);
 
    class Factory;
 
    struct parameters_type
        : enable_preconditioned_iterative_solver_factory_parameters<
              parameters_type, Factory> {
        std::pair<detail::coeff_type<value_type>,
                  detail::coeff_type<value_type>>
            GKO_FACTORY_PARAMETER_VECTOR(foci,
                                         detail::coeff_type<value_type>{0},
                                         detail::coeff_type<value_type>{1});
 
        initial_guess_mode GKO_FACTORY_PARAMETER_SCALAR(
            default_initial_guess, initial_guess_mode::provided);
    };
 
    GKO_ENABLE_LIN_OP_FACTORY(Chebyshev, parameters, Factory);
    GKO_ENABLE_BUILD_METHOD(Factory);
 
    static parameters_type parse(const config::pnode& config,
                                 const config::registry& context,
                                 const config::type_descriptor& td_for_child =
                                     config::make_type_descriptor<ValueType>());
 
protected:
    void apply_impl(const LinOp* b, LinOp* x) const override;
 
    template <typename VectorType>
    void apply_dense_impl(const VectorType* b, VectorType* x,
                          initial_guess_mode guess) const;
 
    void apply_impl(const LinOp* alpha, const LinOp* b, const LinOp* beta,
                    LinOp* x) const override;
 
    void apply_with_initial_guess_impl(const LinOp* b, LinOp* x,
                                       initial_guess_mode guess) const override;
 
    void apply_with_initial_guess_impl(const LinOp* alpha, const LinOp* b,
                                       const LinOp* beta, LinOp* x,
                                       initial_guess_mode guess) const override;
 
    explicit Chebyshev(std::shared_ptr<const Executor> exec);
 
    explicit Chebyshev(const Factory* factory,
                       std::shared_ptr<const LinOp> system_matrix);
 
private:
    std::shared_ptr<const LinOp> solver_{};
    detail::coeff_type<value_type> center_;
    detail::coeff_type<value_type> foci_direction_;
};
 
 
template <typename ValueType>
struct workspace_traits<Chebyshev<ValueType>> {
    using Solver = Chebyshev<ValueType>;
    // number of vectors used by this workspace
    static int num_vectors(const Solver&);
    // number of arrays used by this workspace
    static int num_arrays(const Solver&);
    // array containing the num_vectors names for the workspace vectors
    static std::vector<std::string> op_names(const Solver&);
    // array containing the num_arrays names for the workspace vectors
    static std::vector<std::string> array_names(const Solver&);
    // array containing all varying scalar vectors (independent of problem size)
    static std::vector<int> scalars(const Solver&);
    // array containing all varying vectors (dependent on problem size)
    static std::vector<int> vectors(const Solver&);
 
    // residual vector
    constexpr static int residual = 0;
    // inner solution vector
    constexpr static int inner_solution = 1;
    // update solution
    constexpr static int update_solution = 2;
    // constant 1.0 scalar
    constexpr static int one = 3;
    // constant -1.0 scalar
    constexpr static int minus_one = 4;
 
    // stopping status array
    constexpr static int stop = 0;
};
 
 
}  // namespace solver
}  // namespace gko
 
 
#endif  // GKO_PUBLIC_CORE_SOLVER_CHEBYSHEV_HPP_