/* define the identity element for an Observer */
struct NullObserver {
  void before_timestepping(const view_constgbx gbxs) const {}

  void after_timestepping() const {}

  unsigned int next_step(const unsigned int t) const {
    return std::numeric_limits<unsigned int>::max();
  }

  bool on_step(const unsigned int t) const { return false; }

  void at_start_step(const unsigned int t, const view_constgbx gbxs,
                     const view_constsupers supers) const {}

  Monitor auto get_monitor() const { return NullMonitor{}; }
};