what I really confuse is I need to set the kernel size to 5 instead of 3 to get above result:
unfold = nn.Unfold(kernel_size=5, padding=1)

for an input tensor like below, why the kernel size is 5, I don’t really understand
tensor([[[[ 0.,  1.,  2.,  3.,  4.],
          [ 5.,  6.,  7.,  8.,  9.],
          [10., 11., 12., 13., 14.],
          [15., 16., 17., 18., 19.],
          [20., 21., 22., 23., 24.]]]])