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

h = w * x + b          # -4.0
a = torch.relu(h)      #  0.0
loss = (a - y) ** 2    # (0 - 2)² = 4.0
loss.backward()

print(w.grad.item())   # 0.0
print(b.grad.item())   # 0.0