Hi,
I know that im2col()'s backward is col2im(), and I’m studying how F.unfold() triggers the backward pass of  im2col().
I noticed there are functions like im2col_backward_cuda()/im2col_backward_out_cuda()/im2col_backward_out_cuda_template() in Pytorch repository 1. However, when searching for these names, the only hit is the file itself.
My question is:

Are the above backward functions ever called at all?
How is im2col()'s backward triggered?

Thank you!