loss = (a1A + a2A + a3A )- (b1A + b2A + b3A +b4*A)
the original a1 a2 a3 are some padded matrices representing some character strings
same for b1, b2, b3, b4
The values for a2  is dependent on a1, but this should not be in the computational graph. Same, the values for a3 is dependent on a2.
However, the value of a1 is the output of feeding some values to lstm, same for a2, a3, b1 …
So I expect that during back propagation, the loss will be back propagated to the b4A operation then through the lstm, and then through the b3A operation then throught the lstm etc…
They use the same LSTM, therefore I expect the parameters in LSTM are back propagated multiple times…