Code sample in this section:https://github.com/Devinterview-io/pytorch-interview-questions?tab=readme-ov-file#code-example-autograd-in-action

x.grad is the partial derivative ofw with respect tox, which is$\frac{\partial{w}}{\partial{z}}$$\frac{\partial{z}}{\partial{x}}$
$\frac{\partial{w}}{\partial{z}}$ =$2x$
$\frac{\partial{z}}{\partial{x}}$ =$y$
Thus$\frac{\partial{w}}{\partial{z}}$$\frac{\partial{z}}{\partial{x}}$ =$2zy$.$y$ was initialized to 4, and$z$ =$xy$ = 12. So$2zy$ = 2 times 12 times 4 = 96.

Likewise you can work out the value ofy.grad using the chain rule as well, and it's 72.