new_contents: import numpy as np
  def mse(observation,predicted):
      m1,n1 = observation.shape
      m2,n2 = predicted.shape
      assert m1 == m2, "different number of examples"
      assert n1 == n2, "different number of features"
      return np.mean(np.square(observation-predicted))
  
subject: Create mean_squared_error.py