Mean Squared Error
    
    :param exp: expected values
    :type exp: list of float
    :param obs: observed values
    :type obs: list of float

def mse(exp, obs):
    """Mean Squared Error
    
    :param exp: expected values
    :type exp: list of float
    :param obs: observed values
    :type obs: list of float
    """
    assert len(exp) == len(obs)
    return numpy.mean((numpy.array(exp) - numpy.array(obs)) ** 2)