isai.hpp

// SPDX-FileCopyrightText: 2017 - 2025 The Ginkgo authors
//
// SPDX-License-Identifier: BSD-3-Clause
 
#ifndef GKO_PUBLIC_CORE_PRECONDITIONER_ISAI_HPP_
#define GKO_PUBLIC_CORE_PRECONDITIONER_ISAI_HPP_
 
 
#include <memory>
 
#include <ginkgo/core/base/composition.hpp>
#include <ginkgo/core/base/exception_helpers.hpp>
#include <ginkgo/core/base/executor.hpp>
#include <ginkgo/core/base/lin_op.hpp>
#include <ginkgo/core/config/config.hpp>
#include <ginkgo/core/config/registry.hpp>
#include <ginkgo/core/matrix/csr.hpp>
#include <ginkgo/core/matrix/dense.hpp>
 
 
namespace gko {
namespace preconditioner {
 

enum struct isai_type { lower, upper, general, spd };

template <isai_type IsaiType, typename ValueType, typename IndexType>
class Isai : public EnableLinOp<Isai<IsaiType, ValueType, IndexType>>,
             public Transposable {
    friend class EnableLinOp<Isai>;
    friend class EnablePolymorphicObject<Isai, LinOp>;
    friend class Isai<isai_type::general, ValueType, IndexType>;
    friend class Isai<isai_type::lower, ValueType, IndexType>;
    friend class Isai<isai_type::upper, ValueType, IndexType>;
    friend class Isai<isai_type::spd, ValueType, IndexType>;
    GKO_ASSERT_SUPPORTED_VALUE_AND_INDEX_TYPE;
 
public:
    using value_type = ValueType;
    using index_type = IndexType;
    using transposed_type =
        Isai<IsaiType == isai_type::general ? isai_type::general
             : IsaiType == isai_type::spd   ? isai_type::spd
             : IsaiType == isai_type::lower ? isai_type::upper
                                            : isai_type::lower,
             ValueType, IndexType>;
    using Comp = Composition<ValueType>;
    using Csr = matrix::Csr<ValueType, IndexType>;
    using Dense = matrix::Dense<ValueType>;
    static constexpr isai_type type{IsaiType};

    std::shared_ptr<const typename std::conditional<IsaiType == isai_type::spd,
                                                    Comp, Csr>::type>
    get_approximate_inverse() const
    {
        return as<typename std::conditional<IsaiType == isai_type::spd, Comp,
                                            Csr>::type>(approximate_inverse_);
    }

    Isai& operator=(const Isai& other);

    Isai& operator=(Isai&& other);

    Isai(const Isai& other);

    Isai(Isai&& other);
 
    GKO_CREATE_FACTORY_PARAMETERS(parameters, Factory)
    {
        bool GKO_FACTORY_PARAMETER_SCALAR(skip_sorting, false);

        int GKO_FACTORY_PARAMETER_SCALAR(sparsity_power, 1);

        size_type GKO_FACTORY_PARAMETER_SCALAR(excess_limit, 0u);

        std::shared_ptr<const LinOpFactory> GKO_DEFERRED_FACTORY_PARAMETER(
            excess_solver_factory);
 
        remove_complex<value_type> GKO_FACTORY_PARAMETER_SCALAR(
            excess_solver_reduction,
            static_cast<remove_complex<value_type>>(1e-6));
    };
 
    GKO_ENABLE_LIN_OP_FACTORY(Isai, 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, IndexType>());
 
    std::unique_ptr<LinOp> transpose() const override;
 
    std::unique_ptr<LinOp> conj_transpose() const override;
 
protected:
    explicit Isai(std::shared_ptr<const Executor> exec)
        : EnableLinOp<Isai>(std::move(exec))
    {}

    explicit Isai(const Factory* factory,
                  std::shared_ptr<const LinOp> system_matrix)
        : EnableLinOp<Isai>(factory->get_executor(), system_matrix->get_size()),
          parameters_{factory->get_parameters()}
    {
        const auto skip_sorting = parameters_.skip_sorting;
        const auto power = parameters_.sparsity_power;
        const auto excess_limit = parameters_.excess_limit;
        generate_inverse(system_matrix, skip_sorting, power, excess_limit,
                         static_cast<remove_complex<value_type>>(
                             parameters_.excess_solver_reduction));
        if (IsaiType == isai_type::spd) {
            auto inv = share(as<Csr>(approximate_inverse_));
            auto inv_transp = share(inv->conj_transpose());
            approximate_inverse_ =
                Composition<ValueType>::create(inv_transp, inv);
        }
    }
 
    void apply_impl(const LinOp* b, LinOp* x) const override
    {
        approximate_inverse_->apply(b, x);
    }
 
    void apply_impl(const LinOp* alpha, const LinOp* b, const LinOp* beta,
                    LinOp* x) const override
    {
        approximate_inverse_->apply(alpha, b, beta, x);
    }
 
private:
    void generate_inverse(std::shared_ptr<const LinOp> to_invert,
                          bool skip_sorting, int power, index_type excess_limit,
                          remove_complex<value_type> excess_solver_reduction);
 
private:
    std::shared_ptr<LinOp> approximate_inverse_;
};
 
 
template <typename ValueType = default_precision, typename IndexType = int32>
using LowerIsai = Isai<isai_type::lower, ValueType, IndexType>;
 
template <typename ValueType = default_precision, typename IndexType = int32>
using UpperIsai = Isai<isai_type::upper, ValueType, IndexType>;
 
template <typename ValueType = default_precision, typename IndexType = int32>
using GeneralIsai = Isai<isai_type::general, ValueType, IndexType>;
 
template <typename ValueType = default_precision, typename IndexType = int32>
using SpdIsai = Isai<isai_type::spd, ValueType, IndexType>;
 
 
}  // namespace preconditioner
}  // namespace gko
 
 
#endif  // GKO_PUBLIC_CORE_PRECONDITIONER_ISAI_HPP_