Summary: GRU is different than LSTM that it only has hidden states but no cell states. So in this case, reusing the code of _LSTM is problematic, as we need to delete the part of creating cell state, and change many other places that use hard-coded 4 (hidden_all, hidden, cell_all, cell) into 2 (hidden_all, hidden). Otherwise GRU will break during the backward pass, when the optimizer tries to apply gradient to each of the parameters, because cell state is never used, so it does not have gradients for the corresponding parameters (i.e., cell_state_w, cell_state_b).
Differential Revision: D5589309
fbshipit-source-id: f5af67dfe0842acd68223f6da3e96a81639e8049
Summary:
Moved sigmoid, tanh, and _prepare_lstm (renamed) to a util file.
Also renamed _prepare_lstm to _preapare_rnn since it is being used for both setting up and LSTM and GRU model.
The reason for this commit is to allow the creation of GRU Op and testing code without copying and pasting code for sigmoid, tanh, and setting up an rnn unit op mode.
Reviewed By: jamesr66a
Differential Revision: D5363675
fbshipit-source-id: 352bd70378031f1d81606c9267e625c6728b18fd
