enumerations.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) 2019-2025 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_ENUMERATIONS_HPP
#define OPENKALMAN_ENUMERATIONS_HPP

namespace OpenKalman
{
  enum struct triangle_type : int {
    none, 
    any, 
    lower, 
    upper, 
    diagonal, 
    // \todo strict_diagonal,
    //< A specific diagonal object for rank 2k (k:ℕ) tensors in which each element is zero unless its
    //< indices can be divided into two identical sequences.
    //< (Examples, component x[1,0,2,1,0,2] in rank-6 tensor x or component y[2,5,2,5] in rank-4 tensor y.)
  };


  constexpr triangle_type
  operator * (triangle_type a, triangle_type b)
  {
    if (a == triangle_type::diagonal or
        b == triangle_type::diagonal or
        (a == triangle_type::upper and b == triangle_type::lower) or
        (a == triangle_type::lower and b == triangle_type::upper)) return triangle_type::diagonal;
    if (a == triangle_type::lower or
        b == triangle_type::lower) return triangle_type::lower;
    if (a == triangle_type::upper or
        b == triangle_type::upper) return triangle_type::upper;
    if (a == triangle_type::any or
        b == triangle_type::any) return triangle_type::any;
    return triangle_type::none;
  }


  constexpr triangle_type
  operator + (triangle_type a, triangle_type b)
  {
    if (a == triangle_type::diagonal) return b;
    if (b == triangle_type::diagonal) return a;
    if (a == triangle_type::lower and b == triangle_type::lower) return triangle_type::lower;
    if (a == triangle_type::upper and b == triangle_type::upper) return triangle_type::upper;
    return triangle_type::none;
  }


  enum struct HermitianAdapterType : int {
    none = static_cast<int>(triangle_type::none), 
    any = static_cast<int>(triangle_type::diagonal), 
    lower = static_cast<int>(triangle_type::lower), 
    upper = static_cast<int>(triangle_type::upper), 
  };

}


#endif