# allennlp.modules.augmented_lstm¶

An LSTM with Recurrent Dropout and the option to use highway connections between layers.

class allennlp.modules.augmented_lstm.AugmentedLstm(input_size: int, hidden_size: int, go_forward: bool = True, recurrent_dropout_probability: float = 0.0, use_highway: bool = True, use_input_projection_bias: bool = True)[source]

Bases: torch.nn.modules.module.Module

An LSTM with Recurrent Dropout and the option to use highway connections between layers. Note: this implementation is slower than the native Pytorch LSTM because it cannot make use of CUDNN optimizations for stacked RNNs due to the highway layers and variational dropout.

Parameters
input_sizeint, required.

The dimension of the inputs to the LSTM.

hidden_sizeint, required.

The dimension of the outputs of the LSTM.

go_forward: bool, optional (default = True)

The direction in which the LSTM is applied to the sequence. Forwards by default, or backwards if False.

recurrent_dropout_probability: float, optional (default = 0.0)

The dropout probability to be used in a dropout scheme as stated in A Theoretically Grounded Application of Dropout in Recurrent Neural Networks . Implementation wise, this simply applies a fixed dropout mask per sequence to the recurrent connection of the LSTM. Dropout is not applied to the output sequence nor the last hidden state that is returned, it is only applied to all previous hidden states.

use_highway: bool, optional (default = True)

Whether or not to use highway connections between layers. This effectively involves reparameterising the normal output of an LSTM as:

gate = sigmoid(W_x1 * x_t + W_h * h_t)
output = gate * h_t  + (1 - gate) * (W_x2 * x_t)

use_input_projection_biasbool, optional (default = True)

Whether or not to use a bias on the input projection layer. This is mainly here for backwards compatibility reasons and will be removed (and set to False) in future releases.

Returns
output_accumulatorPackedSequence

The outputs of the LSTM for each timestep. A tensor of shape (batch_size, max_timesteps, hidden_size) where for a given batch element, all outputs past the sequence length for that batch are zero tensors.

forward(self, inputs:torch.nn.utils.rnn.PackedSequence, initial_state:Union[Tuple[torch.Tensor, torch.Tensor], NoneType]=None)[source]
Parameters
inputsPackedSequence, required.

A tensor of shape (batch_size, num_timesteps, input_size) to apply the LSTM over.

initial_stateTuple[torch.Tensor, torch.Tensor], optional, (default = None)

A tuple (state, memory) representing the initial hidden state and memory of the LSTM. Each tensor has shape (1, batch_size, output_dimension).

Returns
A PackedSequence containing a torch.FloatTensor of shape
(batch_size, num_timesteps, output_dimension) representing
the outputs of the LSTM per timestep and a tuple containing
the LSTM state, with shape (1, batch_size, hidden_size) to
match the Pytorch API.
reset_parameters(self)[source]