def pretrain(self, train_set, validation_set=None):
        """Perform Unsupervised pretraining of the autoencoder."""
        self.do_pretrain = True

        def set_params_func(autoenc, autoencgraph):
            params = autoenc.get_parameters(graph=autoencgraph)
            self.encoding_w_.append(params['enc_w'])
            self.encoding_b_.append(params['enc_b'])

        return SupervisedModel.pretrain_procedure(
            self, self.autoencoders, self.autoencoder_graphs,
            set_params_func=set_params_func, train_set=train_set,
            validation_set=validation_set)
Perform Unsupervised pretraining of the autoencoder.