Pythorch损失值不改变

Question

我根据本文编写了一个模块：http://www.wildml.com/2015/12/implementing-a-cnn-for-text-classification-in-tensorflow/

其思想是将输入传递到多个流中，然后合并到一起并连接到FC层。我将源代码分成3个自定义模块：TextClassifyCnnNet>；FlatCnnLayer>；FilterLayer

过滤层：

class FilterLayer(nn.Module):
    def __init__(self, filter_size, embedding_size, sequence_length, out_channels=128):
        super(FilterLayer, self).__init__()

        self.model = nn.Sequential(
            nn.Conv2d(1, out_channels, (filter_size, embedding_size)),
            nn.ReLU(inplace=True),
            nn.MaxPool2d((sequence_length - filter_size + 1, 1), stride=1)
        )

        for m in self.modules():
            if isinstance(m, nn.Conv2d):
                n = m.kernel_size[0] * m.kernel_size[1] * m.out_channels
                m.weight.data.normal_(0, math.sqrt(2. / n))

    def forward(self, x):
        return self.model(x)

扁平图层：

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textClassifyCnnet（主模块）：

class TextClassifyCnnNet(nn.Module):
    def __init__(self, embedding_size, sequence_length, num_classes, filter_sizes=[3, 4, 5], out_channels=128):
        super(TextClassifyCnnNet, self).__init__()

        self.flat_layer = FlatCnnLayer(embedding_size, sequence_length, filter_sizes=filter_sizes,
                                       out_channels=out_channels)

        self.model = nn.Sequential(
            self.flat_layer,
            nn.Linear(out_channels * len(filter_sizes), num_classes)
        )

    def forward(self, x):
        x = self.model(x)

        return x


def fit(net, data, save_path):
    if torch.cuda.is_available():
        net = net.cuda()

    for param in list(net.parameters()):
        print(type(param.data), param.size())

    optimizer = optim.Adam(net.parameters(), lr=0.01, weight_decay=0.1)

    X_train, X_test = data['X_train'], data['X_test']
    Y_train, Y_test = data['Y_train'], data['Y_test']

    X_valid, Y_valid = data['X_valid'], data['Y_valid']

    n_batch = len(X_train) // batch_size

    for epoch in range(1, n_epochs + 1):  # loop over the dataset multiple times
        net.train()
        start = 0
        end = batch_size

        for batch_idx in range(1, n_batch + 1):
            # get the inputs
            x, y = X_train[start:end], Y_train[start:end]
            start = end
            end = start + batch_size

            # zero the parameter gradients
            optimizer.zero_grad()

            # forward + backward + optimize
            predicts = _get_predict(net, x)
            loss = _get_loss(predicts, y)
            loss.backward()
            optimizer.step()

            if batch_idx % display_step == 0:
                print('Train Epoch: {} [{}/{} ({:.0f}%)]\tLoss: {:.6f}'.format(
                    epoch, batch_idx * len(x), len(X_train), 100. * batch_idx / (n_batch + 1), loss.data[0]))

        # print statistics
        if epoch % display_step == 0 or epoch == 1:
            net.eval()
            valid_predicts = _get_predict(net, X_valid)
            valid_loss = _get_loss(valid_predicts, Y_valid)
            valid_accuracy = _get_accuracy(valid_predicts, Y_valid)
            print('\r[%d] loss: %.3f - accuracy: %.2f' % (epoch, valid_loss.data[0], valid_accuracy * 100))

    print('\rFinished Training\n')

    net.eval()

    test_predicts = _get_predict(net, X_test)
    test_loss = _get_loss(test_predicts, Y_test).data[0]
    test_accuracy = _get_accuracy(test_predicts, Y_test)
    print('Test loss: %.3f - Test accuracy: %.2f' % (test_loss, test_accuracy * 100))

    torch.save(net.flat_layer.state_dict(), save_path)


def _get_accuracy(predicts, labels):
    predicts = torch.max(predicts, 1)[1].data[0]
    return np.mean(predicts == labels)


def _get_predict(net, x):
    # wrap them in Variable
    inputs = torch.from_numpy(x).float()
    # convert to cuda tensors if cuda flag is true
    if torch.cuda.is_available:
        inputs = inputs.cuda()
    inputs = Variable(inputs)
    return net(inputs)


def _get_loss(predicts, labels):
    labels = torch.from_numpy(labels).long()
    # convert to cuda tensors if cuda flag is true
    if torch.cuda.is_available:
        labels = labels.cuda()
    labels = Variable(labels)
    return F.cross_entropy(predicts, labels)

似乎每个历元的参数都会稍微更新一点，整个过程的精度都保持不变。虽然在Tensorflow中使用相同的实现和相同的参数，但它可以正确运行。在

我是新来的Pythorch，所以可能我的指示有问题，请帮我找出原因。谢谢您！在

注：我尝试使用F.nll_loss+F.log_softmax而不是F.cross_entropy。理论上，它应该返回相同的结果，但实际上打印出另一个结果（但它仍然是错误的损失值）

Answer 1

我已经看到在您的原始代码中，weight_decayterm被设置为0.1。weight_decay用于正则化网络参数。这个术语可能太强了，所以正则化太多了。{cd1>尝试减少^的值。在

用于计算机视觉任务中的卷积神经网络。weight_decay项通常设置为5e-4或{}。我不熟悉文本分类。这些值可能会对你开箱即用，或者你必须通过反复试验来调整它。在

如果对你有用，请告诉我。在

Answer 2

我意识到Adam优化器中的L2_丢失使loss值保持不变（我还没有在其他优化器中尝试过）。当我删除L2_丢失时，它会起作用：

# optimizer = optim.Adam(net.parameters(), lr=0.01, weight_decay=0.1)
optimizer = optim.Adam(model.parameters(), lr=0.001)

===更新（请参阅上面的答案了解更多详细信息！）===

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