import tensorflow as tf

        lstm_cell_fw = tf.contrib.rnn.LSTMBlockFusedCell(self.params['lstm_size'])
        lstm_cell_bw = tf.contrib.rnn.LSTMBlockFusedCell(self.params['lstm_size'])
        lstm_cell_bw = tf.contrib.rnn.TimeReversedFusedRNN(lstm_cell_bw)
        output_fw, _ = lstm_cell_fw(t, dtype=tf.float32,
