import tensorflow as tf

        self.w_attn_2 = tf.get_variable("w_2", [self.lstm_size, self.lstm_size])
        self.v_attn = tf.get_variable("v", [self.lstm_size, 1])

  def _build_sampler(self, prev_c=None, prev_h=None, use_bias=False):
    """Build the sampler ops and the log_prob ops."""

    print ("-" * 80)
    print ("Build controller sampler")

    anchors = tf.TensorArray(
      tf.float32, size=self.num_cells + 2, clear_after_read=False)
    anchors_w_1 = tf.TensorArray(
      tf.float32, size=self.num_cells + 2, clear_after_read=False)
    arc_seq = tf.TensorArray(tf.int32, size=self.num_cells * 4)
    if prev_c is None:
      assert prev_h is None, "prev_c and prev_h must both be None"
      prev_c = [tf.zeros([1, self.lstm_size], tf.float32)
                for _ in range(self.lstm_num_layers)]
