x = torch.tensor(2.0)
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
a = torch.relu(h)
loss = (a - y) ** 2

loss.backward()

print(f"loss  = {loss.item()}")     # 9.0
print(f"dL/dw = {w.grad.item()}")   # 12.0
print(f"dL/db = {b.grad.item()}")   # 6.0