add error handlings

        energies : array-like, shape (n_samples)

            Calculated sample energies.

        """

        if self.sess is None:

            raise Exception("Trained model does not exist.")

        energies = self.sess.run(self.energy, feed_dict={self.input:x})

        return energies

    def save(self, fdir):

        if self.sess is None:

            raise Exception("Trained model does not exist.")

        if not exists(fdir):

            makedirs(fdir)