Math used for BiLSTMLayer in predict function

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I am trying to convert a trained Bi-LSTM network to use on another platform, and wish to know the exact math used for the BiLSTM layer in Matlab predict function, just like the equations used in the LSTM layer Architecture section on this page.
The reason I am asking is that, the output given by the "predict" function is different from the output I calculate using my own code.
So I am trying to figure out the problem.
(pretty sure that I got the parameters like the input weights, recurrectweight, and bias correctly.)
The way I was calculating is as follows:
% forward
ft = sigmoid(wf*xt + uf*ht +bf);
it = sigmoid(wi*xt + ui*ht +bi);
ot = sigmoid(wo*xt + uo*ht +bo);
ctb = tanh(wc*xt + uc*ht +bc);
ct = ft.*ct + it.*ctb;
ht = ot.*tanh(ct);
% backward
xtb = flip(xt);
ftb = sigmoid(wfb*xtb + ufb*htb +bfb);
itb = sigmoid(wib*xtb + uib*htb +bib);
otb = sigmoid(wob*xtb + uob*htb +bob);
ctbb = tanh(wcb*xtb + ucb*htb +bcb);
ctb = ftb.*ctb + itb.*ctbb;
htb = otb.*tanh(ctb);
% output hidden states
Ht = [ht;htb];
Can anyone help? Thank you very much!

Accepted Answer

David Willingham
David Willingham on 27 Jan 2022
Hi James,
One option for exporting is to export the network to onnx format using exportONNXnetwork. Once exported you could either import the onnx version into the other framework as well as look at how the network wax exported.
  3 Comments
David Willingham
David Willingham on 28 Jan 2022
I checked with our developers and what you have looks correct. Without having both your full MATLAB code and python? code it may be difficult for us to find the reason why they maybe different.
James He
James He on 28 Jan 2022
Hi David, I really appreciate your assistance.
Maybe I will have to look into other options.
Thanks.

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