``
First, whether thegrad_tensorsargument was specified or not, there is a call to the [_make_grads](https://github.com/pytorch/pytorch/blob/bc2c6edaf163b1a1330e37a6e34caf8c553e4755/torch/autograd/__init__.py#L30-L74) function. This is used to check the providedgrad_tensorsor to specify the default value for them by looking at thetensorsargument values’ shapes. Check the first blog post for details on the default value for thegrad_tensors` of the backward pass. This function just provides the vector of the vector jacobian product if it was not initially specified.