code: def reverse_velocity_kalman_model():
      '''Return a KalmanState set up to model going backwards in time'''
      om = np.array([[1,0,0,0], [0, 1, 0, 0]])
      tm = np.array([[1,0,-1,0],
                     [0,1,0,-1],
                     [0,0,1,0],
                     [0,0,0,1]])
      return KalmanState(om, tmf reverse_velocity_kalman_model():
      '''Return a KalmanState set up to model going backwards in time'''
      om = np.array([[1,0,0,0], [0, 1, 0, 0]])
      tm = np.array([[1,0,-1,0],
                     [0,1,0,-1],
                     [0,0,1,0],
                     [0,0,0,1]])
      return KalmanState(om, tm)
docs: Return a KalmanState set up to model going backwards in time