Function raw_rnn

tensorflow/python/ops/rnn.py:940–1259

Creates an `RNN` specified by RNNCell `cell` and loop function `loop_fn`. **NOTE: This method is still in testing, and the API may change.** This function is a more primitive version of `dynamic_rnn` that provides more direct access to the inputs each iteration. It also provides more cont

(cell,
            loop_fn,
            parallel_iterations=None,
            swap_memory=False,
            scope=None)

@tf_export(v1=["nn.raw_rnn"])
def raw_rnn(cell,
            loop_fn,
            parallel_iterations=None,
            swap_memory=False,
            scope=None):
  """Creates an `RNN` specified by RNNCell `cell` and loop function `loop_fn`.

  **NOTE: This method is still in testing, and the API may change.**

  This function is a more primitive version of `dynamic_rnn` that provides
  more direct access to the inputs each iteration.  It also provides more
  control over when to start and finish reading the sequence, and
  what to emit for the output.

  For example, it can be used to implement the dynamic decoder of a seq2seq
  model.

  Instead of working with `Tensor` objects, most operations work with
  `TensorArray` objects directly.

  The operation of `raw_rnn`, in pseudo-code, is basically the following:

  ```python
  time = tf.constant(0, dtype=tf.int32)
  (finished, next_input, initial_state, emit_structure, loop_state) = loop_fn(
      time=time, cell_output=None, cell_state=None, loop_state=None)
  emit_ta = TensorArray(dynamic_size=True, dtype=initial_state.dtype)
  state = initial_state
  while not all(finished):
    (output, cell_state) = cell(next_input, state)
    (next_finished, next_input, next_state, emit, loop_state) = loop_fn(
        time=time + 1, cell_output=output, cell_state=cell_state,
        loop_state=loop_state)
    # Emit zeros and copy forward state for minibatch entries that are finished.
    state = tf.where(finished, state, next_state)
    emit = tf.where(finished, tf.zeros_like(emit_structure), emit)
    emit_ta = emit_ta.write(time, emit)
    # If any new minibatch entries are marked as finished, mark these.
    finished = tf.logical_or(finished, next_finished)
    time += 1
  return (emit_ta, state, loop_state)
  ```

  with the additional properties that output and state may be (possibly nested)
  tuples, as determined by `cell.output_size` and `cell.state_size`, and
  as a result the final `state` and `emit_ta` may themselves be tuples.

  A simple implementation of `dynamic_rnn` via `raw_rnn` looks like this:

  ```python
  inputs = tf.compat.v1.placeholder(shape=(max_time, batch_size, input_depth),
                          dtype=tf.float32)
  sequence_length = tf.compat.v1.placeholder(shape=(batch_size,),
  dtype=tf.int32)
  inputs_ta = tf.TensorArray(dtype=tf.float32, size=max_time)
  inputs_ta = inputs_ta.unstack(inputs)

  cell = tf.compat.v1.nn.rnn_cell.LSTMCell(num_units)