Objectorientedprogramming in pytorch

[km_proton]

could you please answer this question

Use of .backward()

what is the use of backward i cannot understand x=torch.tensor(3.,requires_grad=True) w=torch.tensor(2.,requires_grad=True) b=torch.tensor(4.,requires_grad=True) y=w*x+b y.backward() x.grad w.grad b.grad could you please explain use of .backward class also use of .grad