我无法确定我是否错误地计算了损失，但是 我的training_loss没有收敛；我正在使用Pytorch网站上的蚂蚁和蜜蜂数据集：
https://pytorch.org/tutorials/beginner/transfer_learning_tutorial.html（只需向下滚动一点）
root_dir = "main_dir"
image_transforms = transforms.Compose([
transforms.Resize((224,224)),
transforms.ToTensor(),
transforms.Normalize(
mean=[0.485, 0.456, 0.406],
std=[0.229, 0.224, 0.225]
)])
# First we create train_data and val_data
train = ImageFolder(root = os.path.join(root_dir, 'train'),
transform=image_transforms)
#valid data
valid = ImageFolder(root = os.path.join(root_dir, 'val'),
transform=image_transforms)
train_dataloader = DataLoader(train, batch_size=4,
shuffle=True)
valid_dataloader = DataLoader(valid, batch_size=4,
shuffle=True)
optimizer = optim.SGD(model.parameters(), lr=0.0001, momentum=0.9)
criterion = nn.CrossEntropyLoss() #loss function we want to use
def train_model(optimizer, criterion, model, epochs, train_loader, valid_loader):
for epoch in range(epochs):
print('Epoch {}/{}'.format(epoch, epochs - 1))
print('-' * 10)
train_loss = 0.0
model.train()
for inputs, labels in train_loader:
inputs = inputs.to(device)
labels = labels.to(device)
#allow backprop
with torch.set_grad_enabled(True):
optimizer.zero_grad()
outputs = model(inputs)
loss = criterion(outputs, labels) #uses softmax -> cross entropy
loss.backward() # calculate the gradients
optimizer.step() # apply gradients to parameters
# statistics
train_loss += loss.item() * inputs.size(0) # total loss instead of average loss
print('total training loss {:.3f}'.format(train_loss))
print('training_loss per sample {:.5f}'.format(train_loss/len(train_loader.dataset)))
model.eval()
valid_corrects = 0.0
total_valid_loss = 0.0
for inputs, labels in valid_loader:
inputs = inputs.to(device)
labels = labels.to(device)
#disallow backprop
with torch.set_grad_enabled(False):
outputs = model(inputs)
loss = criterion(outputs, labels)
_, preds = torch.max(F.softmax(outputs), dim = 1) #values and indicies
total_valid_loss += loss.item() * inputs.size(0) # total loss instead of average loss
valid_corrects += torch.sum(preds == labels.data)
valid_loss_per_sample = total_valid_loss/len(valid_loader.dataset)
accuracy = valid_corrects.item()/len(valid_loader.dataset)
print('total valid loss {:.3f}'.format(total_valid_loss))
print('valid_loss per sample {:.3f}'.format(valid_loss_per_sample))
print('total accuracy {:.3f}'.format(accuracy))
if __name__ == "__main__":
epochs = 25
train_model(optimizer, criterion, model, epochs, train_dataloader, valid_dataloader)
这是我的亏损经历了24个纪元的样子（如您所见） 它似乎没有收敛。我试图改变学习率，但这似乎并没有太大帮助）
Epoch 5/24
----------
total training loss 35.477
training_loss per sample 0.14540
total valid loss 46.130
valid_loss per sample 0.302
total accuracy 0.850
Epoch 6/24
----------
total training loss 57.476
training_loss per sample 0.23556
total valid loss 55.434
valid_loss per sample 0.362
total accuracy 0.837
Epoch 7/24
----------
total training loss 66.397
training_loss per sample 0.27212
total valid loss 41.781
valid_loss per sample 0.273
total accuracy 0.869
Epoch 8/24
----------
total training loss 61.362
training_loss per sample 0.25148
total valid loss 45.502
Epoch 21/24
----------
total training loss 47.409
training_loss per sample 0.19430
total valid loss 50.288
valid_loss per sample 0.329
total accuracy 0.837
Epoch 22/24
----------
total training loss 35.873
training_loss per sample 0.14702
total valid loss 49.597
valid_loss per sample 0.324
total accuracy 0.863
Epoch 23/24
----------
total training loss 30.655
training_loss per sample 0.12563
total valid loss 44.393
valid_loss per sample 0.290
total accuracy 0.869
Epoch 24/24
----------
total training loss 54.373
training_loss per sample 0.22284
total valid loss 60.207
valid_loss per sample 0.394
total accuracy 0.850