Set requires_grad=True to stop tracking history?

Well, I am not sure whether I understand the tutorila right or not. In the AUTOGRAD: AUTOMATIC DIFFERENTIATION tutorial, it says that " If you set its attribute .requires_grad as True , it starts to track all operations on it." However, in the later tutorial, it says " You can also stop autograd from tracking history on Tensors with .requires_grad=True either by wrapping the code block in with torch.no_grad():" To stop autograd from tracking history on tensors, don’t we should set the requires_grad = False? Is it a conflict?

No, you won’t be able to set requires_grad=False for any non-leaf tensor and will get the following error:

RuntimeError: you can only change requires_grad flags of leaf variables. If you want to use a computed variable in a subgraph that doesn't require differentiation use var_no_grad = var.detach().

Use the torch.no_grad() block, which will make sure that Autograd won’t track any operations in this block, or detach() the tensor as described in the tutorial.