GRU¶

class GRU(hidden_size, num_layers=1, layout='TNC', dropout=0, bidirectional=False, input_size=0, i2h_weight_initializer=None, h2h_weight_initializer=None, i2h_bias_initializer='zeros', h2h_bias_initializer='zeros', dtype='float32', **kwargs)¶

Applies a multi-layer gated recurrent unit (GRU) RNN to an input sequence. Note: this is an implementation of the cuDNN version of GRUs (slight modification compared to Cho et al. 2014; the reset gate \(r_t\) is applied after matrix multiplication).

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

(34)¶\[\begin{split}\begin{array}{ll} r_t = sigmoid(W_{ir} x_t + b_{ir} + W_{hr} h_{(t-1)} + b_{hr}) \\ i_t = sigmoid(W_{ii} x_t + b_{ii} + W_{hi} h_{(t-1)} + b_{hi}) \\ n_t = \tanh(W_{in} x_t + b_{in} + r_t * (W_{hn} h_{(t-1)} + b_{hn})) \\ h_t = (1 - i_t) * n_t + i_t * h_{(t-1)} \\ \end{array}\end{split}\]

where \(h_t\) is the hidden state at time t, \(x_t\) is the hidden state of the previous layer at time t or \(input_t\) for the first layer, and \(r_t\), \(i_t\), \(n_t\) are the reset, input, and new gates, respectively.

Parameters:

hidden_size: int

The number of features in the hidden state h

num_layers: int, default 1

Number of recurrent layers.

layout : str, default ‘TNC’

The format of input and output tensors. T, N and C stand for sequence length, batch size, and feature dimensions respectively.

dropout: float, default 0

If non-zero, introduces a dropout layer on the outputs of each RNN layer except the last layer

bidirectional: bool, default False

If True, becomes a bidirectional RNN.

i2h_weight_initializer : str or Initializer

Initializer for the input weights matrix, used for the linear transformation of the inputs.

h2h_weight_initializer : str or Initializer

Initializer for the recurrent weights matrix, used for the linear transformation of the recurrent state.

i2h_bias_initializer : str or Initializer

Initializer for the bias vector.

h2h_bias_initializer : str or Initializer

Initializer for the bias vector.

dtype : str, default ‘float32’

Type to initialize the parameters and default states to

input_size: int, default 0

The number of expected features in the input x. If not specified, it will be inferred from input.

prefix : str or None

Prefix of this Block.

params : ParameterDict or None

Shared Parameters for this Block.

Inputs:

data: input tensor with shape (sequence_length, batch_size, input_size) when layout is “TNC”. For other layouts, dimensions are permuted accordingly using transpose() operator which adds performance overhead. Consider creating batches in TNC layout during data batching step.
states: initial recurrent state tensor with shape (num_layers, batch_size, num_hidden). If bidirectional is True, shape will instead be (2*num_layers, batch_size, num_hidden). If states is None, zeros will be used as default begin states.

Outputs:

out: output tensor with shape (sequence_length, batch_size, num_hidden) when layout is “TNC”. If bidirectional is True, output shape will instead be (sequence_length, batch_size, 2*num_hidden)
out_states: output recurrent state tensor with the same shape as states. If states is None out_states will not be returned.

Examples

>>> layer = mx.gluon.rnn.GRU(100, 3)
>>> layer.initialize()
>>> input = mx.nd.random.uniform(shape=(5, 3, 10))
>>> # by default zeros are used as begin state
>>> output = layer(input)
>>> # manually specify begin state.
>>> h0 = mx.nd.random.uniform(shape=(3, 3, 100))
>>> output, hn = layer(input, h0)