2. 尝试不同的激活函数，哪个效果最好？

activations = [
    nn.ReLU(),
    nn.LeakyReLU(), nn.PReLU(), nn.RReLU(), nn.ReLU6(),
    nn.ELU(), nn.SELU(), nn.GELU(),
    nn.Tanh(), nn.Tanhshrink(),
    nn.Sigmoid(),
    nn.Softmax(), nn.Softmin(),
]

for activation in activations:
    net = nn.Sequential(nn.Flatten(),
                        nn.Linear(784, 256),
                        activation, # nn.ReLU(),
                        nn.Linear(256, 10))

    def init_weights(m):
        if type(m) == nn.Linear:
            nn.init.normal_(m.weight, std=0.01)

    net.apply(init_weights);

    batch_size, lr, num_epochs = 256, 0.1, 10
    loss = nn.CrossEntropyLoss(reduction='none')
    trainer = torch.optim.SGD(net.parameters(), lr=lr)

    train_iter, test_iter = d2l.load_data_fashion_mnist(batch_size)
    try:
        d2l.train_ch3(net, train_iter, test_iter, loss, num_epochs, trainer)
    except Exception as ex:
        print(ex)