Applies a multi-layer gated recurrent unit (GRU) RNN to an input sequence.

For each element in the input sequence, each layer computes the following function:

Usage

nn_gru(
  input_size,
  hidden_size,
  num_layers = 1,
  bias = TRUE,
  batch_first = FALSE,
  dropout = 0,
  bidirectional = FALSE,
  ...
)

Arguments

input_size: The number of expected features in the input x
hidden_size: The number of features in the hidden state h
num_layers: Number of recurrent layers. E.g., setting num_layers=2 would mean stacking two GRUs together to form a stacked GRU, with the second GRU taking in outputs of the first GRU and computing the final results. Default: 1
bias: If FALSE, then the layer does not use bias weights b_ih and b_hh. Default: TRUE
batch_first: If TRUE, then the input and output tensors are provided as (batch, seq, feature). Default: FALSE
dropout: If non-zero, introduces a Dropout layer on the outputs of each GRU layer except the last layer, with dropout probability equal to dropout. Default: 0
bidirectional: If TRUE, becomes a bidirectional GRU. Default: FALSE
...: currently unused.

Details

$$ \begin{array}{ll} r_t = \sigma(W_{ir} x_t + b_{ir} + W_{hr} h_{(t-1)} + b_{hr}) \\ z_t = \sigma(W_{iz} x_t + b_{iz} + W_{hz} h_{(t-1)} + b_{hz}) \\ n_t = \tanh(W_{in} x_t + b_{in} + r_t (W_{hn} h_{(t-1)}+ b_{hn})) \\ h_t = (1 - z_t) n_t + z_t h_{(t-1)} \end{array} $$

where $h_t$ is the hidden state at time t, $x_t$ is the input at time t, $h_{(t-1)}$ is the hidden state of the previous layer at time t-1 or the initial hidden state at time 0, and $r_t$, $z_t$, $n_t$ are the reset, update, and new gates, respectively. $\sigma$ is the sigmoid function.

Note

All the weights and biases are initialized from $\mathcal{U}(-\sqrt{k}, \sqrt{k})$ where $k = \frac{1}{\mbox{hidden\_size}}$

Inputs

Inputs: input, h_0

input of shape (seq_len, batch, input_size): tensor containing the features of the input sequence. The input can also be a packed variable length sequence. See nn_utils_rnn_pack_padded_sequence() for details.
h_0 of shape (num_layers * num_directions, batch, hidden_size): tensor containing the initial hidden state for each element in the batch. Defaults to zero if not provided.

Outputs

Outputs: output, h_n

output of shape (seq_len, batch, num_directions * hidden_size): tensor containing the output features h_t from the last layer of the GRU, for each t. If a PackedSequence has been given as the input, the output will also be a packed sequence. For the unpacked case, the directions can be separated using output$view(c(seq_len, batch, num_directions, hidden_size)), with forward and backward being direction 0 and 1 respectively. Similarly, the directions can be separated in the packed case.
h_n of shape (num_layers * num_directions, batch, hidden_size): tensor containing the hidden state for t = seq_len Like output, the layers can be separated using h_n$view(num_layers, num_directions, batch, hidden_size).

Attributes

weight_ih_l[k] : the learnable input-hidden weights of the $\mbox{k}^{th}$ layer (W_ir|W_iz|W_in), of shape (3*hidden_size x input_size)
weight_hh_l[k] : the learnable hidden-hidden weights of the $\mbox{k}^{th}$ layer (W_hr|W_hz|W_hn), of shape (3*hidden_size x hidden_size)
bias_ih_l[k] : the learnable input-hidden bias of the $\mbox{k}^{th}$ layer (b_ir|b_iz|b_in), of shape (3*hidden_size)
bias_hh_l[k] : the learnable hidden-hidden bias of the $\mbox{k}^{th}$ layer (b_hr|b_hz|b_hn), of shape (3*hidden_size)

Examples

if (torch_is_installed()) {

rnn <- nn_gru(10, 20, 2)
input <- torch_randn(5, 3, 10)
h0 <- torch_randn(2, 3, 20)
output <- rnn(input, h0)
}