def train(train_features, test_features, train_labels, test_labels, num_epochs=400): loss = nn.MSELoss(reduction='none') input_shape = train_features.shape[-1] # 不设置偏置，因为我们已经在多项式中实现了它 net = nn.Sequential(nn.Linear(input_shape, 1, bias=False)) batch_size = min(10, train_labels.shape[0]) train_iter = d2l.load_array((train_features, train_labels.reshape(-1,1)), batch_size) test_iter = d2l.load_array((test_features, test_labels.reshape(-1,1)), batch_size, is_train=False) trainer = torch.optim.SGD(net.parameters(), lr=0.01) animator = d2l.Animator(xlabel='epoch', ylabel='loss', yscale='log', xlim=[1, num_epochs], ylim=[1e-3, 1e2], legend=['train', 'test']) for epoch in range(num_epochs): d2l.train_epoch_ch3(net, train_iter, loss, trainer) if epoch == 0 or (epoch + 1) % 20 == 0: animator.add(epoch + 1, (evaluate_loss(net, train_iter, loss), evaluate_loss(net, test_iter, loss))) print('weight:', net[0].weight.data.numpy())

这是一个用于训练线性回归模型的函数，包含五个参数：

- train_features: 训练数据的特征，类型为numpy.ndarray
- test_features: 测试数据的特征，类型为numpy.ndarray
- train_labels: 训练数据的标签，类型为numpy.ndarray
- test_labels: 测试数据的标签，类型为numpy.ndarray
- num_epochs: 训练轮数，默认为400

该函数的主要实现逻辑如下：

1. 定义损失函数为均方误差(MSE)损失函数
2. 定义线性回归模型，其中偏置项(bias)被设置为False，因为已经在多项式中实现了它
3. 设置batch_size为10或者训练集样本数中的最小值，定义训练集和测试集的数据迭代器
4. 定义优化器为随机梯度下降(SGD)优化器，学习率为0.01
5. 定义一个绘图工具，用于绘制损失函数的变化曲线
6. 循环训练num_epochs轮，每轮训练中使用d2l.train_epoch_ch3函数进行训练，该函数实现了一个标准的训练过程，包括向前传播、计算损失、反向传播、更新参数等步骤
7. 在每20轮训练后，记录并绘制训练集和测试集的损失值
8. 输出训练后的权重

训练完成后，可以通过该函数返回的net对象来进行预测。

相关问题

def train(model, train_features, train_labels, test_features, test_labels, num_epochs, learning_rate, weight_decay, batch_size): 帮我加个注释

# 定义训练函数，接收模型、训练特征、训练标签、测试特征、测试标签、训练轮数、学习率、权重衰减和批大小等参数
def train(model, train_features, train_labels, test_features, test_labels,
num_epochs, learning_rate, weight_decay, batch_size):
# 定义损失函数和优化器
criterion = nn.CrossEntropyLoss()
optimizer = optim.Adam(model.parameters(), lr=learning_rate, weight_decay=weight_decay)
# 定义训练和测试数据集
train_dataset = TensorDataset(train_features, train_labels)
test_dataset = TensorDataset(test_features, test_labels)
# 定义训练和测试数据集的加载器
train_loader = DataLoader(train_dataset, batch_size=batch_size, shuffle=True)
test_loader = DataLoader(test_dataset, batch_size=batch_size, shuffle=False)
# 开始训练模型
for epoch in range(num_epochs):
# 训练模式
model.train()
train_loss = 0.0
train_acc = 0.0
for features, labels in train_loader:
# 将特征和标签放入设备中
features = features.to(device)
labels = labels.to(device)
# 清空优化器的梯度
optimizer.zero_grad()
# 前向传播
outputs = model(features)
# 计算损失
loss = criterion(outputs, labels)
# 反向传播
loss.backward()
optimizer.step()
# 计算训练损失
train_loss += loss.item() * features.size(0)
# 计算训练准确率
_, preds = torch.max(outputs, 1)
train_acc += torch.sum(preds == labels.data)
# 计算平均训练损失和准确率
train_loss = train_loss / len(train_features)
train_acc = train_acc / len(train_features)
# 测试模式
model.eval()
test_loss = 0.0
test_acc = 0.0
with torch.no_grad():
for features, labels in test_loader:
# 将特征和标签放入设备中
features = features.to(device)
labels = labels.to(device)
# 前向传播
outputs = model(features)
# 计算损失
loss = criterion(outputs, labels)
# 计算测试损失
test_loss += loss.item() * features.size(0)
# 计算测试准确率
_, preds = torch.max(outputs, 1)
test_acc += torch.sum(preds == labels.data)
# 计算平均测试损失和准确率
test_loss = test_loss / len(test_features)
test_acc = test_acc / len(test_features)
# 输出训练和测试结果
print('Epoch [{}/{}], Train Loss: {:.4f}, Train Acc: {:.4f}, Test Loss: {:.4f}, Test Acc: {:.4f}'
.format(epoch+1, num_epochs, train_loss, train_acc, test_loss, test_acc))
# 返回训练好的模型
return model

LDAM损失函数pytorch代码如下：class LDAMLoss(nn.Module): def init(self, cls_num_list, max_m=0.5, weight=None, s=30): super(LDAMLoss, self).init() m_list = 1.0 / np.sqrt(np.sqrt(cls_num_list)) m_list = m_list * (max_m / np.max(m_list)) m_list = torch.cuda.FloatTensor(m_list) self.m_list = m_list assert s > 0 self.s = s if weight is not None: weight = torch.FloatTensor(weight).cuda() self.weight = weight self.cls_num_list = cls_num_list def forward(self, x, target): index = torch.zeros_like(x, dtype=torch.uint8) index_float = index.type(torch.cuda.FloatTensor) batch_m = torch.matmul(self.m_list[None, :], index_float.transpose(1,0)) # 0,1 batch_m = batch_m.view((16, 1)) # size=(batch_size, 1) (-1,1) x_m = x - batch_m output = torch.where(index, x_m, x) if self.weight is not None: output = output * self.weight[None, :] target = torch.flatten(target) # 将 target 转换成 1D Tensor logit = output * self.s return F.cross_entropy(logit, target, weight=self.weight) 模型部分参数如下：# 设置全局参数 model_lr = 1e-5 BATCH_SIZE = 16 EPOCHS = 50 DEVICE = torch.device('cuda:0' if torch.cuda.is_available() else 'cpu') use_amp = True use_dp = True classes = 7 resume = None CLIP_GRAD = 5.0 Best_ACC = 0 #记录最高得分 use_ema=True model_ema_decay=0.9998 start_epoch=1 seed=1 seed_everything(seed) # 数据增强 mixup mixup_fn = Mixup( mixup_alpha=0.8, cutmix_alpha=1.0, cutmix_minmax=None, prob=0.1, switch_prob=0.5, mode='batch', label_smoothing=0.1, num_classes=classes) # 读取数据集 dataset_train = datasets.ImageFolder('/home/adminis/hpy/ConvNextV2_Demo/RAF-DB/RAF/train', transform=transform) dataset_test = datasets.ImageFolder("/home/adminis/hpy/ConvNextV2_Demo/RAF-DB/RAF/valid", transform=transform_test) 帮我用pytorch实现模型在模型训练中使用LDAM损失函数

好的，下面是使用LDAM损失函数训练模型的代码：

import torch.optim as optim
from torch.optim.lr_scheduler import CosineAnnealingLR
from torch.utils.data import DataLoader

# 定义LDAM损失函数
class LDAMLoss(nn.Module):
    def __init__(self, cls_num_list, max_m=0.5, weight=None, s=30):
        super(LDAMLoss, self).__init__()
        m_list = 1.0 / np.sqrt(np.sqrt(cls_num_list))
        m_list = m_list * (max_m / np.max(m_list))
        m_list = torch.cuda.FloatTensor(m_list)
        self.m_list = m_list
        assert s > 0
        self.s = s
        if weight is not None:
            weight = torch.FloatTensor(weight).cuda()
        self.weight = weight
        self.cls_num_list = cls_num_list

    def forward(self, x, target):
        index = torch.zeros_like(x, dtype=torch.uint8)
        index_float = index.type(torch.cuda.FloatTensor)
        batch_m = torch.matmul(self.m_list[None, :], index_float.transpose(1,0)) # 0,1
        batch_m = batch_m.view((x.size(0), 1)) # size=(batch_size, 1)
        x_m = x - batch_m
        output = torch.where(index, x_m, x)
        if self.weight is not None:
            output = output * self.weight[None, :]
        target = torch.flatten(target) # 将 target 转换成 1D Tensor
        logit = output * self.s
        return F.cross_entropy(logit, target, weight=self.weight)

# 定义模型
model = models.resnet18(pretrained=True)
num_ftrs = model.fc.in_features
model.fc = nn.Linear(num_ftrs, classes)
model.to(DEVICE)

# 定义优化器和学习率调整器
optimizer = optim.Adam(model.parameters(), lr=model_lr)
scheduler = CosineAnnealingLR(optimizer, T_max=EPOCHS, eta_min=1e-6)

# 定义LDAM损失函数
cls_num_list = [len(dataset_train[dataset_train.targets == t]) for t in range(classes)]
criterion = LDAMLoss(cls_num_list)

# 定义数据加载器
train_loader = DataLoader(dataset_train, batch_size=BATCH_SIZE, shuffle=True, num_workers=4, pin_memory=True)
test_loader = DataLoader(dataset_test, batch_size=BATCH_SIZE, shuffle=False, num_workers=4, pin_memory=True)

# 训练模型
best_acc = 0.0
for epoch in range(start_epoch, EPOCHS + 1):
    model.train()
    train_loss = 0.0
    train_corrects = 0
    for inputs, labels in train_loader:
        inputs, labels = inputs.to(DEVICE), labels.to(DEVICE)
        if use_dp:
            inputs, labels = dp(inputs, labels)
        if use_amp:
            with amp.autocast():
                inputs, labels = mixup_fn(inputs, labels)
                outputs = model(inputs)
                loss = criterion(outputs, labels)
            scaler.scale(loss).backward()
            scaler.unscale_(optimizer)
            torch.nn.utils.clip_grad_norm_(model.parameters(), CLIP_GRAD)
            scaler.step(optimizer)
            scaler.update()
        else:
            inputs, labels_a, labels_b, lam = mixup_fn(inputs, labels)
            outputs = model(inputs)
            loss = mixup_criterion(criterion, outputs, labels_a, labels_b, lam)
            loss.backward()
            torch.nn.utils.clip_grad_norm_(model.parameters(), CLIP_GRAD)
            optimizer.step()
            optimizer.zero_grad()
        train_loss += loss.item() * inputs.size(0)
        _, preds = torch.max(outputs, 1)
        train_corrects += torch.sum(preds == labels.data)
    train_loss /= len(dataset_train)
    train_acc = train_corrects.double() / len(dataset_train)

    model.eval()
    test_loss = 0.0
    test_corrects = 0
    with torch.no_grad():
        for inputs, labels in test_loader:
            inputs, labels = inputs.to(DEVICE), labels.to(DEVICE)
            outputs = model(inputs)
            loss = criterion(outputs, labels)
            test_loss += loss.item() * inputs.size(0)
            _, preds = torch.max(outputs, 1)
            test_corrects += torch.sum(preds == labels.data)
    test_loss /= len(dataset_test)
    test_acc = test_corrects.double() / len(dataset_test)

    # 更新最佳模型
    if test_acc > best_acc:
        if use_ema:
            ema_model.load_state_dict(model.state_dict())
        best_acc = test_acc

    # 更新学习率
    scheduler.step()

    # 打印训练结果
    print('Epoch [{}/{}], Train Loss: {:.4f}, Train Acc: {:.4f}, Test Loss: {:.4f}, Test Acc: {:.4f}'.format(
        epoch, EPOCHS, train_loss, train_acc, test_loss, test_acc))