我使用mxnet训练VQA模型,输入是(6244,)
矢量,输出是单个标签
在我的时代,损失永远不会改变,但准确性在小范围内振荡,前5个时期
Epoch 1. Loss: 2.7262569132562255, Train_acc 0.06867348986554285
Epoch 2. Loss: 2.7262569132562255, Train_acc 0.06955649207304837
Epoch 3. Loss: 2.7262569132562255, Train_acc 0.06853301224162152
Epoch 4. Loss: 2.7262569132562255, Train_acc 0.06799116997792494
Epoch 5. Loss: 2.7262569132562255, Train_acc 0.06887417218543046
这是一个多类分类问题,每个答案标签代表一个类,所以我使用softmax作为最后一层和交叉熵来评估损失,它们的代码如下
那么为什么损失永远不会改变?......我只是直接从cross_entropy
得到
trainer = gluon.Trainer(net.collect_params(), 'sgd', {'learning_rate': 0.01})
loss = gluon.loss.SoftmaxCrossEntropyLoss()
epochs = 10
moving_loss = 0.
best_eva = 0
for e in range(epochs):
for i, batch in enumerate(data_train):
data1 = batch.data[0].as_in_context(ctx)
data2 = batch.data[1].as_in_context(ctx)
data = [data1, data2]
label = batch.label[0].as_in_context(ctx)
with autograd.record():
output = net(data)
cross_entropy = loss(output, label)
cross_entropy.backward()
trainer.step(data[0].shape[0])
moving_loss = np.mean(cross_entropy.asnumpy()[0])
train_accuracy = evaluate_accuracy(data_train, net)
print("Epoch %s. Loss: %s, Train_acc %s" % (e, moving_loss, train_accuracy))
评估功能如下
def evaluate_accuracy(data_iterator, net, ctx=mx.cpu()):
numerator = 0.
denominator = 0.
metric = mx.metric.Accuracy()
data_iterator.reset()
for i, batch in enumerate(data_iterator):
with autograd.record():
data1 = batch.data[0].as_in_context(ctx)
data2 = batch.data[1].as_in_context(ctx)
data = [data1, data2]
label = batch.label[0].as_in_context(ctx)
output = net(data)
metric.update([label], [output])
return metric.get()[1]
问题在mxnet讨论论坛here上提出并回答。在计算精度时,无需使用autograd.record
示波器记录计算图。尝试改为:
def evaluate_accuracy(data_iterator, net, ctx=mx.cpu()):
metric = mx.metric.Accuracy()
data_iterator.reset()
for i, batch in enumerate(data_iterator):
data1 = batch.data[0].as_in_context(ctx)
data2 = batch.data[1].as_in_context(ctx)
data = [data1, data2]
label = batch.label[0].as_in_context(ctx)
output = net(data)
metric.update([label], [output])
return metric.get()[1]