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


  num_layers = 1,
  bias = TRUE,
  batch_first = FALSE,
  dropout = 0,
  bidirectional = FALSE,



The number of expected features in the input x


The number of features in the hidden state h


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


If FALSE, then the layer does not use bias weights b_ih and b_hh. Default: TRUE


If TRUE, then the input and output tensors are provided as (batch, seq, feature). Default: FALSE


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


If TRUE, becomes a bidirectional GRU. Default: FALSE


currently unused.


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

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.


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


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: 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).


  • 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)


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)