How to use a lstm in a reversed direction?

Hi, everyone! I am a newer on Pytorch. I have a question:
I want to build a BiLSTM which is different with the one provided by the Pytorch.
My idea BiLSTM is a forward LSTM from the left to right in a sentence. Then, each output of the forward LSTM hi will be feed into the reversed LSTM as the input. Just as the picture below shows.

Question: Is there any way i can implement this process? Specially, when it comes to batching, it is a bit difficult to implement it.

If I don’t misunderstand, it seems to be straightforward to implement like:

h_f, _ = self.forward_lstm(x) # say h_f has size (batch, seq, dim)
inv_idx = torch.arange(h_f.size(1)-1, -1, -1).long()
inv_h_f = h_f.index_select(1, inv_idx)
h_b, _ = self.backward_lstm(inv_h_f)

Then, you can manipulate h_b depending on your need. (be careful with the order as the input is reversed)

Thanks for your advice. I’m trying it

This seems to forward padding tokens ahead of reverse sequence