code: def velocity_kalman_model():
      '''Return a KalmanState set up to model objects with constant velocity
  
      The observation and measurement vectors are i,j.
      The state vector is i,j,vi,vj
      '''
      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 velocity_kalman_model():
      '''Return a KalmanState set up to model objects with constant velocity
  
      The observation and measurement vectors are i,j.
      The state vector is i,j,vi,vj
      '''
      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 objects with constant velocity
  
      The observation and measurement vectors are i,j.
      The state vector is i,j,vi,vj