I’m pretty convinced this will be a silly question, and still I’d ask it.
Look at the example at http://pytorch.org/tutorials/beginner/blitz/autograd_tutorial.html 17
How the gradient out with respect to x is calculated is pretty clear and makes sense according to the chain rule.
What I don’t understand is why the other leaves have no gradient. E.g., if you print(y.grad) it equals to None.
Why’s that? After all, y  (or z) is another variable (in fact, Variable) involved in the chain rule…