code: def predmean(self, xp): 
          
          out = np.empty_like(xp)
          for i in range(3):
              out[:, i] = xp[:, i] + self.delta * xp[:, i+3]  # position
              out[:, i+3] = xp[:, i+3]                      # velocity 
          return out
docs: Expectation of X_t given X_{t-1}=xp