Actually, they are feature maps (with 4x4 grids: 16 cells).
i=0: first cell of S0 needs to concatenate with whole of 16 cells in S1, then appended in S2.
i=1: second cell of S0 needs to concatenate with whole of 16 cells in S1, then appended in S2.
…
i=15: 16th cell of S0 needs to concatenate with whole of 16 cells in S1, then appended in S2.
that’s why I used " torch.cat((S0[:,i,None], S1), dim=1)"
?