【发布时间】：2021-07-19 05:12:48
【问题描述】：
我正在尝试对 MNIST 数据集进行二进制分类。偶数为 0 级，奇数为 1 级。我正在使用 VGG 的简化版本。 我的神经网络有一个损失和一个保持不变的准确性。 我想说我的模型在将目标转换为二进制目标之前达到了 90% 以上的准确率，所以可能有问题。 这里我把目标改成二进制：
for i in range(10):
idx = (train_set.targets==i)
if (i == 0) or ((i % 2) == 0): train_set.targets[idx] = 0
else: train_set.targets[idx] = 1
for i in range(10):
idx = (test_set.targets==i)
if (i == 0) or ((i % 2) == 0): test_set.targets[idx] = 0
else: test_set.targets[idx] = 1
这是我的网：
class VGG16(nn.Module):
def __init__(self, num_classes):
super(VGG16, self).__init__()
# calculate same padding:
# (w - k + 2*p)/s + 1 = o
# => p = (s(o-1) - w + k)/2
self.block_1 = nn.Sequential(
nn.Conv2d(in_channels=1,
out_channels=64,
kernel_size=(3, 3),
stride=(1, 1),
# (1(32-1)- 32 + 3)/2 = 1
padding=1),
nn.BatchNorm2d(64),
nn.ReLU(),
nn.Conv2d(in_channels=64,
out_channels=64,
kernel_size=(3, 3),
stride=(1, 1),
padding=1),
nn.BatchNorm2d(64),
nn.ReLU(),
nn.MaxPool2d(kernel_size=(2, 2),
stride=(2, 2))
)
self.block_2 = nn.Sequential(
nn.Conv2d(in_channels=64,
out_channels=128,
kernel_size=(3, 3),
stride=(1, 1),
padding=1),
nn.BatchNorm2d(128),
nn.ReLU(),
nn.Conv2d(in_channels=128,
out_channels=128,
kernel_size=(3, 3),
stride=(1, 1),
padding=1),
nn.BatchNorm2d(128),
nn.ReLU(),
nn.MaxPool2d(kernel_size=(2, 2),
stride=(2, 2))
)
self.block_3 = nn.Sequential(
nn.Conv2d(in_channels=128,
out_channels=256,
kernel_size=(3, 3),
stride=(1, 1),
padding=1),
nn.BatchNorm2d(256),
nn.ReLU(),
nn.Conv2d(in_channels=256,
out_channels=256,
kernel_size=(3, 3),
stride=(1, 1),
padding=1),
nn.BatchNorm2d(256),
nn.ReLU(),
nn.Conv2d(in_channels=256,
out_channels=256,
kernel_size=(3, 3),
stride=(1, 1),
padding=1),
nn.BatchNorm2d(256),
nn.ReLU(),
nn.MaxPool2d(kernel_size=(2, 2),
stride=(2, 2))
)
self.block_4 = nn.Sequential(
nn.Conv2d(in_channels=256,
out_channels=512,
kernel_size=(3, 3),
stride=(1, 1),
padding=1),
nn.BatchNorm2d(512),
nn.ReLU(),
nn.Conv2d(in_channels=512,
out_channels=512,
kernel_size=(3, 3),
stride=(1, 1),
padding=1),
nn.BatchNorm2d(512),
nn.ReLU(),
nn.Conv2d(in_channels=512,
out_channels=512,
kernel_size=(3, 3),
stride=(1, 1),
padding=1),
nn.BatchNorm2d(512),
nn.ReLU(),
nn.MaxPool2d(kernel_size=(2, 2),
stride=(2, 2))
)
self.classifier = nn.Sequential(
nn.Linear(2048, 4096),
nn.ReLU(True),
nn.Dropout(p=0.65),
nn.Linear(4096, 4096),
nn.ReLU(True),
nn.Dropout(p=0.65),
nn.Linear(4096, num_classes),
nn.Sigmoid()
)
for m in self.modules():
if isinstance(m, torch.nn.Conv2d) or isinstance(m, torch.nn.Linear):
nn.init.kaiming_uniform_(m.weight, mode='fan_in', nonlinearity='leaky_relu')
# nn.init.xavier_normal_(m.weight)
if m.bias is not None:
m.bias.detach().zero_()
# self.avgpool = nn.AdaptiveAvgPool2d((7, 7))
def forward(self, x):
x = self.block_1(x)
x = self.block_2(x)
x = self.block_3(x)
x = self.block_4(x)
# x = self.avgpool(x)
x = x.view(x.size(0), -1)
x = self.classifier(x)
return x
#logits = self.classifier(x)
#probas = F.softmax(logits, dim=1)
# probas = nn.Softmax(logits)
#return probas
# return logits
# Define an optimizier
import torch.optim as optim
optimizer = optim.SGD(model.parameters(), lr = 0.01)
# Define a loss
criterion = nn.BCELoss()
def train(net, loaders, optimizer, criterion, epochs=20, dev=dev, save_param = False, model_name="valerio"):
try:
net = net.to(dev)
#print(net)
# Initialize history
history_loss = {"train": [], "val": [], "test": []}
history_accuracy = {"train": [], "val": [], "test": []}
# Store the best val accuracy
best_val_accuracy = 0
# Process each epoch
for epoch in range(epochs):
# Initialize epoch variables
sum_loss = {"train": 0, "val": 0, "test": 0}
sum_accuracy = {"train": 0, "val": 0, "test": 0}
# Process each split
for split in ["train", "val", "test"]:
if split == "train":
net.train()
else:
net.eval()
# Process each batch
for (input, labels) in loaders[split]:
# Move to CUDA
input = input.to(dev)
labels = labels.to(dev)
# Reset gradients
optimizer.zero_grad()
# Compute output
pred = net(input)
labels = labels.unsqueeze(1)
labels = labels.float()
loss = criterion(pred, labels)
# Update loss
sum_loss[split] += loss.item()
# Check parameter update
if split == "train":
# Compute gradients
loss.backward()
# Optimize
optimizer.step()
# Compute accuracy
_,pred_labels = pred.max(1)
batch_accuracy = (pred_labels == labels).sum().item()/input.size(0)
# Update accuracy
sum_accuracy[split] += batch_accuracy
# Compute epoch loss/accuracy
epoch_loss = {split: sum_loss[split]/len(loaders[split]) for split in ["train", "val", "test"]}
epoch_accuracy = {split: sum_accuracy[split]/len(loaders[split]) for split in ["train", "val", "test"]}
# Store params at the best validation accuracy
if save_param and epoch_accuracy["val"] > best_val_accuracy:
#torch.save(net.state_dict(), f"{net.__class__.__name__}_best_val.pth")
torch.save(net.state_dict(), f"{model_name}_best_val.pth")
best_val_accuracy = epoch_accuracy["val"]
# Update history
for split in ["train", "val", "test"]:
history_loss[split].append(epoch_loss[split])
history_accuracy[split].append(epoch_accuracy[split])
# Print info
print(f"Epoch {epoch+1}:",
f"TrL={epoch_loss['train']:.4f},",
f"TrA={epoch_accuracy['train']:.4f},",
f"VL={epoch_loss['val']:.4f},",
f"VA={epoch_accuracy['val']:.4f},",
f"TeL={epoch_loss['test']:.4f},",
f"TeA={epoch_accuracy['test']:.4f},")
except KeyboardInterrupt:
print("Interrupted")
finally:
# Plot loss
plt.title("Loss")
for split in ["train", "val", "test"]:
plt.plot(history_loss[split], label=split)
plt.legend()
plt.show()
# Plot accuracy
plt.title("Accuracy")
for split in ["train", "val", "test"]:
plt.plot(history_accuracy[split], label=split)
plt.legend()
plt.show()
从之前的数字识别模型中，我只改变了目标，最后一层分类器从 10 类变为 1 类 + Sigmoid。我也将交叉熵更改为 BCELoss。我做错了什么？
这些是损失和准确率值：
Epoch 1: TrL=49.0955, TrA=31.4211, VL=49.7285, VA=31.7340, TeL=49.2635, TeA=31.3758,
Epoch 2: TrL=49.0992, TrA=31.4235, VL=49.7285, VA=31.7340, TeL=49.2635, TeA=31.3758,
Epoch 3: TrL=49.0899, TrA=31.4176, VL=49.7285, VA=31.7340, TeL=49.2635, TeA=31.3758,
Epoch 4: TrL=49.0936, TrA=31.4199, VL=49.7285, VA=31.7340, TeL=49.2635, TeA=31.3758,
Epoch 5: TrL=49.0936, TrA=31.4199, VL=49.7285, VA=31.7340, TeL=49.2635, TeA=31.3758,
Epoch 6: TrL=49.0825, TrA=31.4128, VL=49.7285, VA=31.7340, TeL=49.2635, TeA=31.3758,
怎么了？怎么可能用 10 个类达到 90% 以上的准确率，而简化版只有 2 个类，我达到 30% 的准确率？
编辑：将批量大小从 64 增加到 128，准确度达到 60% 并保持不变...
【问题讨论】：
标签： neural-network pytorch conv-neural-network mnist image-classification