def _create_variables_pretrain(self):
        """Create model variables (previous unsupervised pretraining).

        :return: self
        """
        for l, layer in enumerate(self.layers):
            self.encoding_w_[l] = tf.Variable(
                self.encoding_w_[l], name='enc-w-{}'.format(l))
            self.encoding_b_[l] = tf.Variable(
                self.encoding_b_[l], name='enc-b-{}'.format(l))