The basic LSTM seq2seq model with bidirectional encoder.

def lstm_seq2seq_internal_bid_encoder(inputs, targets, hparams, train):
  """The basic LSTM seq2seq model with bidirectional encoder."""
  with tf.variable_scope("lstm_seq2seq_bid_encoder"):
    if inputs is not None:
      inputs_length = common_layers.length_from_embedding(inputs)
      # Flatten inputs.
      inputs = common_layers.flatten4d3d(inputs)
      # LSTM encoder.
      _, final_encoder_state = lstm_bid_encoder(
          inputs, inputs_length, hparams, train, "encoder")
    else:
      inputs_length = None
      final_encoder_state = None
    # LSTM decoder.
    shifted_targets = common_layers.shift_right(targets)
    # Add 1 to account for the padding added to the left from shift_right
    targets_length = common_layers.length_from_embedding(shifted_targets) + 1
    hparams_decoder = copy.copy(hparams)
    hparams_decoder.hidden_size = 2 * hparams.hidden_size
    decoder_outputs, _ = lstm(
        common_layers.flatten4d3d(shifted_targets),
        targets_length,
        hparams_decoder,
        train,
        "decoder",
        initial_state=final_encoder_state)
    return tf.expand_dims(decoder_outputs, axis=2)