'Create model variables (previous unsupervised pretraining).
:return: self'

def _create_variables_pretrain(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])
