LSTM forget gate bias initialization

[ikostrikov]

Some papers suggest to set forget gate bias of LSTMs to a specific value. For example:
http://jmlr.org/proceedings/papers/v37/jozefowicz15.pdf

Is it possible to do using current implementation of LSTM/LSTMCell?

[apaszke]

Yes, the ordering of weights a biases is the same for all implementations and is ingate, forgetgate, cellgate, outgate. You need to initialize the values between 1/4 and 1/2 of the bias vector to the desired value.

[kellywzhang]

What is the difference between "bias_ih" and "bias_hh" in the LSTM and GRU cells? Should both be initialized with ones between 1/4 and 1/2?

[apaszke]

One of them is added to the linear transform of the input, another one to the hidden transform. It's redundant - there could be only one bias, and the model would be equivalent. However, that's what cuDNN does, so we preferred to keep it like that for consistency.