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

def _create_variables_pretrain(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))
