w = torch.tensor(2.0, requires_grad=True)
b = torch.tensor(1.0, requires_grad=True)
x = torch.tensor(3.0)

y = w * x + b            # 2·3 + 1 = 7
loss = (y - 5) ** 2      # (7 - 5)² = 4

loss.backward()

print(w.grad)   # tensor(12.)
print(b.grad)   # tensor(4.)