Hi,
from greping through the pytorch source, I would seem that there is no header with the col2im definition, so you would need to add that somewhere and it might not be considered part of the official api…
In the library, the function is THNN_Floatcol2im
(says objdump -t torch/lib/build/THNN/libTHNN.so.1 | grep col2im).
Best regards
Thomas