Geting new value of calulated tensor

Suppose that I created some computational graph like this

a = torch.autograd.Variable(torch.ones((2,2)), requires_grad=True)
b = a*2

then I update a values like this =*2

My question how can I get new values of b (that should be now [[4,4],[4,4]]) without “creating” new b (e.g. running b = a*2)?

Variables are deprecated since PyTorch 0.4 and the usage of the .data attribute is not recommended, will be removed in the future, and might yield side effects.

That being said, could you explain your use case a bit more and what you are trying to achieve?

Lets say that my b is:

b = 2*a

but to determine that b = 2*a and not b = 3*a or some other coefficient I had to look up giant table. After that I define some loss function and optimize a with Adam. After a is updated I want to find new value of b without doing look up again.
You can argue that I just need to save my coefficient in some variable and use that, but my calculation is really complex and I would spend a lot of time to figure out how to rewrite everything in “tensor” form.

Edit: I am hoping that b = 2*a is already saved somewhere in the graph so I can just “evaluate” it again.