链式传播题

我们定义Q=3a3−b2, 则可以计算出 ∂Q∂a=9a2 且 ∂Q∂b=−2b, 然后我们将a，b的值带入就可以计算出对应的梯度值。 import torch x = torch.tensor(3, dtype=torch.float32, requires_grad=True) y = torch.tensor(4, dtype=torch.float32, requires_grad=True) b = torch.tensor(5, dtype=torch.float32, requires_grad=True) z = x*y + b "Z = xy" print(z) z.backward() print(z.requires_grad, x.grad, y.grad, b.grad) from matplotlib import pyplot as plt import torch data_x = [1, 2, 3] data_y = [2, 4, 6] loss_list = list() a_list = list() alpha = 0.01  def forward(x):    return a * x def lossFunction(x, y):    y_pred = forward(x)    loss = (y_pred - y) ** 2    return loss if __name__ == '__main__':    a = torch.Tensor([7.0])    a.requires_grad = True    for epoch in range(1000):    # for a in np.arange(0, 4, 0.1):        sum_loss = 0        for i in range(3):            sum_loss += lossFunction(data_x[i], data_y[i])            l = lossFunction(data_x[i],data_y[i])            l.backward()            a.data = a.data - alpha*a.grad            a.grad = None            a_list.append(a.data)            # a = gradient(a, data_x[i], data_y[i])        loss_list.append(sum_loss / 3)    print(a_list)    plt.subplot(211)    plt.plot(a_list)    plt.subplot(212)    plt.plot(loss_list)    plt.show()