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  #pragma once
  
  #include <memory>
  
  #include <drake/common/eigen_types.h>
  #include <drake/systems/primitives/matrix_gain.h>
  
  namespace drake_external_examples {
  namespace particles {
  
  /// Makes an NDOF to 6DOF poses mapping system.
  ///
  /// The given matrix @f$ \mathbf{M}_{\mathrm{6,N}} @f$ is
  /// augmented to deal with position and velocity
  /// state input @f$ [\mathbf{q} ; \mathbf{v}] @f$ as follows:
  ///
  /// @f[ M^*_{\mathrm{12,2N}} =
  ///     \begin{bmatrix}
  ///       \mathbf{M}_{\mathrm{6,N}} & \mathbf{0}_{\mathrm{6,N}}
  ///    \\ \mathbf{0}_{\mathrm{6,N}} & \mathbf{M}_{\mathrm{6,N}}
  ///     \end{bmatrix}
  /// @f]
  ///
  /// @param[in] translator 6xN matrix to translate inputs to outputs, where
  /// 0 < N < 6.
  /// @return MatrixGain representing the joint.
  /// @throws std::runtime_error whenever @p translator matrix implies
  /// M DOF output where M is not 6, or an N DOF input where N is not a
  /// positive non-zero integer that is less than 6.
  ///
  /// @tparam T must be a valid Eigen ScalarType.
  ///
  /// @note
  /// Instantiated templates for the following scalar types
  /// @p T are provided:
  /// - double
  ///
  template <typename T>
  std::unique_ptr<typename drake::systems::MatrixGain<T>>
  MakeDegenerateEulerJoint(const drake::MatrixX<T>& translator);
  
  }  // namespace particles
  }  // namespace drake_external_examples
  