make_identity_matrix_like.hpp

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/* This file is part of OpenKalman, a header-only C++ library for
 * Kalman filters and other recursive filters.
 *
 * Copyright (c) 2022-2024 Christopher Lee Ogden <ogden@gatech.edu>
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

#ifndef OPENKALMAN_MAKE_IDENTITY_MATRIX_LIKE_HPP
#define OPENKALMAN_MAKE_IDENTITY_MATRIX_LIKE_HPP

namespace OpenKalman
{
#ifdef __cpp_concepts
  template<indexible T, values::number Scalar = scalar_type_of_t<T>, pattern_collection Descriptors>
  constexpr identity_matrix auto
#else
  template<typename T, typename Scalar = typename scalar_type_of<T>::type, typename Descriptors, std::enable_if_t<
    indexible<T> and values::number<Scalar> and pattern_collection<Descriptors>, int> = 0>
  constexpr auto
#endif
  make_identity_matrix_like(Descriptors&& descriptors)
  {
    decltype(auto) d = coordinates::internal::strip_1D_tail(std::forward<Descriptors>(descriptors));
    using D = decltype(d);
    using Trait = interface::library_interface<stdex::remove_cvref_t<T>>;

    if constexpr (coordinates::euclidean_pattern_collection<D> and interface::make_identity_matrix_defined_for<T, Scalar, D>)
    {
      return Trait::template make_identity_matrix<Scalar>(std::forward<D>(d));
    }
    else if constexpr (interface::make_identity_matrix_defined_for<T, Scalar, decltype(internal::to_euclidean_pattern_collection(d))>)
    {
      auto ed = internal::to_euclidean_pattern_collection(d);
      return attach_pattern(Trait::template make_identity_matrix<Scalar>(ed), std::forward<D>(d));
    }
    else
    {
      return internal::make_constant_diagonal_from_descriptors<T>(values::fixed_value<Scalar, 1>{}, std::forward<D>(d));
    }
  }


#ifdef __cpp_concepts
    template<indexible T, values::number Scalar = scalar_type_of_t<T>, coordinates::pattern...Ds>
    constexpr identity_matrix auto
#else
    template<typename T, typename Scalar = typename scalar_type_of<T>::type, typename...Ds, std::enable_if_t<
      indexible<T> and values::number<Scalar> and (... and coordinates::pattern<Ds>), int> = 0>
    constexpr auto
#endif
    make_identity_matrix_like(Ds&&...ds)
    {
      return make_identity_matrix_like<T, Scalar>(std::tuple {std::forward<Ds>(ds)...});
    }


#ifdef __cpp_concepts
  template<values::number Scalar, indexible Arg>
  constexpr identity_matrix auto
#else
  template<typename Scalar, typename Arg, std::enable_if_t<values::number<Scalar> and indexible<Arg>, int> = 0>
  constexpr auto
#endif
  make_identity_matrix_like(Arg&& arg)
  {
    if constexpr (identity_matrix<Arg> and std::is_same_v<Scalar, scalar_type_of_t<Arg>>) return std::forward<Arg>(arg);
    else return make_identity_matrix_like<Arg, Scalar>(all_vector_space_descriptors(std::forward<Arg>(arg)));
  }


#ifdef __cpp_concepts
  template<indexible Arg>
  constexpr identity_matrix auto
#else
  template<typename Arg, std::enable_if_t<indexible<Arg>, int> = 0>
  constexpr auto
#endif
  make_identity_matrix_like(Arg&& arg)
  {
    return make_identity_matrix_like<scalar_type_of_t<Arg>>(std::forward<Arg>(arg));
  }


}

#endif