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

        :return: self
        """
        for l, layer in enumerate(self.layers):

            w_name = 'enc-w-{}'.format(l)
            b_name = 'enc-b-{}'.format(l)

            self.encoding_w_[l] = tf.Variable(
                self.encoding_w_[l], name=w_name)
            tf.summary.histogram(w_name, self.encoding_w_[l])

            self.encoding_b_[l] = tf.Variable(
                self.encoding_b_[l], name=b_name)
            tf.summary.histogram(b_name, self.encoding_w_[l])