code: def mse(mean, estimator):
      
      return np.mean((np.asarray(estimator) - np.asarray(mean)) ** 2, axis=0)
docs: Description:
          Calculates the Mean Squared Error (MSE) of
          an estimation on flat numpy ndarrays.
      Parameters:
          mean:      actual value (numpy ndarray)
          estimator: estimated value of the mean (numpy ndarray)