state_space.hpp

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/*
 * Copyright © 2025-2026 Akreon LLC
 * SPDX-License-Identifier: Apache-2.0
 */
 
#include "../control_traits.hpp"
 
#pragma once
 
namespace control {
 
template <TimeDomainType Type, linalg::SquareMatrix PlantIn,
          linalg::MatrixContainer ControlIn, linalg::MatrixContainer OutputIn>
struct StateSpace {
  using Plant = linalg::remove_cvref_t<PlantIn>;
  using Control = linalg::remove_cvref_t<ControlIn>;
  using Output = linalg::remove_cvref_t<OutputIn>;
 
  using T = linalg::matrix_scalar_t<Plant>;
  static constexpr std::size_t PlantRows = linalg::mat_rows_v<Plant>;
  static constexpr std::size_t PlantCols = linalg::mat_cols_v<Plant>;
  static constexpr std::size_t ControlRows = linalg::mat_rows_v<Control>;
  static constexpr std::size_t ControlCols = linalg::mat_cols_v<Control>;
  static constexpr std::size_t OutputRows = linalg::mat_rows_v<Output>;
  static constexpr std::size_t OutputCols = linalg::mat_cols_v<Output>;
 
  using Feedthrough = linalg::Matrix<T, OutputRows, ControlCols>;
 
  static_assert(PlantRows == ControlRows,
                "state dim is not aligned between plant and control matrices");
 
  using State = linalg::Vector<T, PlantCols>;
  using Input = linalg::Vector<T, ControlCols>;
 
  constexpr explicit StateSpace(const Plant& A_in, const Control& B_in,
                                const Output& C_in)
      : A(A_in), B(B_in), C(C_in) {}
 
  constexpr explicit StateSpace(const Plant& A_in, const Control& B_in,
                                const Output& C_in, const Feedthrough& D_in)
      : A(A_in), B(B_in), C(C_in), D(D_in) {}
 
  constexpr auto state_update(const State& x, const Input& u) const {
    return A * x + B * u;
  }
 
  constexpr auto output_map(const State& x, const Input& u) const {
    return D.has_value() ? C * x + (*D) * u : C * x;
  }
 
  Plant A;                      
  Control B;                    
  Output C;                     
  std::optional<Feedthrough> D; 
};
 
} // namespace control