OK.
BTW, I found the code wouldn’t run with version 0.4, the error:
RuntimeError: The size of tensor a (25) must match the size of tensor b (3250) at non-singleton dimension 3
x.data + grid_x

where, x.data is a (2, 5, 13, 25) Variable, and grid_x is a [3250] Variable. In version 0.3.1, they are all FloatTensor and work well. May be I have to convert them to FloatTensor?