seq2seq_helpers.py 文件源码

def mask_decoder_reduce(logit, thin_stack_head_next, logit_size, batch_size):
  """Ensures that we can only reduce when the stack has at least 1 item.

  For each batch entry k:
    If thin_stack_head_next == 0, #alternatively, or 1.
      let logit[k][reduce_index] = -np.inf, 
    else don't change.
  """
  # Allow reduce only if at least 1 item on stack, i.e., pointer >= 2.
  update_vals = tf.pack([-np.inf, -np.inf, 0.0])
  update_val = tf.gather(update_vals, 
      tf.minimum(thin_stack_head_next,
      2*tf.ones(tf.pack([batch_size]), dtype=tf.int32)))

  re_filled = tf.fill(tf.pack([batch_size]),
      tf.to_int64(data_utils.REDUCE_ID))
  re_inds = tf.transpose(tf.pack(
      [tf.to_int64(tf.range(batch_size)), re_filled]))
  re_delta = tf.SparseTensor(re_inds, update_val, tf.to_int64(
      tf.pack([batch_size, logit_size])))
  new_logit = logit + tf.sparse_tensor_to_dense(re_delta)
  return new_logit