# Math used for BiLSTMLayer in predict function

4 views (last 30 days)
James He on 27 Jan 2022
Commented: James He on 28 Jan 2022
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!

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.
James He on 28 Jan 2022
Hi David, I really appreciate your assistance.
Maybe I will have to look into other options.
Thanks.