Hi, I have a problem as follow

v_a = Variable(Tensor([1,2,3]),requires_grad=True)
t_a = v_a.data
t_b = t_a * 2
v_b = Variable(t_b, requires_grad=True)
loss = Crit(v_b, target)
loss.backward()

please let me know, How can I get the grad of v_a
I try to exec a code like this, but failed to calculate the grad of v_a
Note: t_b = t_a * 2 just a example, the real operation is complex,  and variable can’t achieve.