composition.hpp

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#ifndef GKO_CORE_BASE_COMPOSITION_HPP_
#define GKO_CORE_BASE_COMPOSITION_HPP_


#include <vector>


#include <ginkgo/core/base/lin_op.hpp>


namespace gko {


template <typename ValueType = default_precision>
class Composition : public EnableLinOp<Composition<ValueType>>,
                    public EnableCreateMethod<Composition<ValueType>> {
    friend class EnablePolymorphicObject<Composition, LinOp>;
    friend class EnableCreateMethod<Composition>;

public:
    using value_type = ValueType;

    const std::vector<std::shared_ptr<const LinOp>> &get_operators() const
        noexcept
    {
        return operators_;
    }

protected:
    explicit Composition(std::shared_ptr<const Executor> exec)
        : EnableLinOp<Composition>(exec)
    {}

    template <typename Iterator,
              typename = xstd::void_t<
                  typename std::iterator_traits<Iterator>::iterator_category>>
    explicit Composition(Iterator begin, Iterator end)
        : EnableLinOp<Composition>([&] {
              if (begin == end) {
                  throw OutOfBoundsError(__FILE__, __LINE__, 1, 0);
              }
              return (*begin)->get_executor();
          }()),
          operators_(begin, end)
    {
        this->set_size(gko::dim<2>{operators_.front()->get_size()[0],
                                   operators_.back()->get_size()[1]});
        for (size_type i = 1; i < operators_.size(); ++i) {
            GKO_ASSERT_CONFORMANT(operators_[i - 1], operators_[i]);
        }
    }

    template <typename... Rest>
    explicit Composition(std::shared_ptr<const LinOp> oper, Rest &&... rest)
        : Composition(std::forward<Rest>(rest)...)
    {
        GKO_ASSERT_CONFORMANT(oper, operators_[0]);
        operators_.insert(begin(operators_), oper);
        this->set_size(gko::dim<2>{operators_.front()->get_size()[0],
                                   operators_.back()->get_size()[1]});
    }

    explicit Composition(std::shared_ptr<const LinOp> oper)
        : EnableLinOp<Composition>(oper->get_executor(), oper->get_size()),
          operators_{oper}
    {}

    void apply_impl(const LinOp *b, LinOp *x) const override;

    void apply_impl(const LinOp *alpha, const LinOp *b, const LinOp *beta,
                    LinOp *x) const override;

private:
    std::vector<std::shared_ptr<const LinOp>> operators_;

    // TODO: solve race conditions when multithreading
    mutable struct cache_struct {
        cache_struct() = default;
        cache_struct(const cache_struct &other) {}
        cache_struct &operator=(const cache_struct &other) { return *this; }

        // TODO: reduce the amount of intermediate vectors we need (careful --
        //       not all of them are of the same size)
        std::vector<std::unique_ptr<LinOp>> intermediate;
    } cache_;
};


}  // namespace gko


#endif  // GKO_CORE_BASE_COMPOSITION_HPP_