In the end, you use .to, just like you would in the “modern” PyTorch idiom.
The variable function not founds in ATen can nonetheless be found using “rgrep” or somesuch on the source, in this case it is found in tools/autograd/templates/python_variable_methods.cpp 13 or also, after you have built PyTorch in torch/csrc/autograd/generated/python_variable_methods.cpp.
Best regards
Thomas