relu_mu = torch.where(is_cross, -0.5*ub*lb/(ub-lb), torch.zeros(lb.size()).to(inputs.device))代码的意思

是根据is_cross的值进行判断，如果为True则返回一个计算后的值，如果为False则返回一个全零的tensor。具体计算方法为：当is_cross为True时，计算出一个值为-0.5*ub*lb/(ub-lb)，否则返回全零的tensor。其中ub和lb分别为上界和下界，inputs.device表示张量所在的设备。

相关问题

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)# 导入数据 train_loader = torch.utils.data.DataLoader(dataset_train, batch_size=BATCH_SIZE, shuffle=True,drop_last=True) test_loader = torch.utils.data.DataLoader(dataset_test, batch_size=BATCH_SIZE, shuffle=False) 帮我用pytorch实现模型在模型训练中使用LDAM损失函数

好的，以下是使用LDAM损失函数训练模型的Pytorch代码：

import torch
import torch.nn as nn
import torch.nn.functional as F
import numpy as np
from torchvision import datasets, transforms
from ldam_loss import LDAMLoss

# 定义模型
class MyModel(nn.Module):
    def __init__(self, num_classes):
        super(MyModel, self).__init__()
        self.num_classes = num_classes
        self.features = nn.Sequential(
            nn.Conv2d(3, 32, kernel_size=3, stride=1, padding=1),
            nn.BatchNorm2d(32),
            nn.ReLU(inplace=True),
            nn.MaxPool2d(kernel_size=2, stride=2),
            nn.Conv2d(32, 64, kernel_size=3, stride=1, padding=1),
            nn.BatchNorm2d(64),
            nn.ReLU(inplace=True),
            nn.MaxPool2d(kernel_size=2, stride=2),
            nn.Conv2d(64, 128, kernel_size=3, stride=1, padding=1),
            nn.BatchNorm2d(128),
            nn.ReLU(inplace=True),
            nn.MaxPool2d(kernel_size=2, stride=2),
        )
        self.classifier = nn.Sequential(
            nn.Linear(128 * 4 * 4, 256),
            nn.ReLU(inplace=True),
            nn.Linear(256, num_classes),
        )

    def forward(self, x):
        x = self.features(x)
        x = x.view(x.size(0), -1)
        x = self.classifier(x)
        return x

# 设置超参数
model_lr = 1e-4
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
use_ema = True
model_ema_decay = 0.9998
start_epoch = 1
seed = 1

# 设置随机种子
def seed_everything(seed):
    torch.manual_seed(seed)
    torch.cuda.manual_seed_all(seed)
    np.random.seed(seed)
seed_everything(seed)

# 定义数据增强
transform = transforms.Compose([
    transforms.Resize(224),
    transforms.RandomHorizontalFlip(),
    transforms.RandomRotation(10),
    transforms.ToTensor(),
    transforms.Normalize(mean=[0.485, 0.456, 0.406],
                         std=[0.229, 0.224, 0.225])
])
transform_test = transforms.Compose([
    transforms.Resize(224),
    transforms.ToTensor(),
    transforms.Normalize(mean=[0.485, 0.456, 0.406],
                         std=[0.229, 0.224, 0.225])
])

# 定义数据集
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)

# 定义数据加载器
train_loader = torch.utils.data.DataLoader(dataset_train, batch_size=BATCH_SIZE, shuffle=True, drop_last=True)
test_loader = torch.utils.data.DataLoader(dataset_test, batch_size=BATCH_SIZE, shuffle=False)

# 定义模型及优化器
model = MyModel(num_classes=classes).to(DEVICE)
optimizer = torch.optim.Adam(model.parameters(), lr=model_lr)

# 使用LDAM损失函数
cls_num_list = [dataset_train.targets.count(i) for i in range(classes)]
criterion = LDAMLoss(cls_num_list=cls_num_list, max_m=0.5, weight=None, s=30)

# 训练模型
for epoch in range(start_epoch, EPOCHS+1):
    model.train()
    for i, (data, target) in enumerate(train_loader):
        data, target = data.to(DEVICE), target.to(DEVICE)
        mixup_data, mixup_target = mixup_fn(data, target)  # 数据增强
        optimizer.zero_grad()
        output = model(mixup_data)
        loss = criterion(output, mixup_target)
        if use_dp:
            loss.backward()
            torch.nn.utils.clip_grad_norm_(model.parameters(), CLIP_GRAD)
        else:
            with amp.scale_loss(loss, optimizer) as scaled_loss:
                scaled_loss.backward()
                torch.nn.utils.clip_grad_norm_(amp.master_params(optimizer), CLIP_GRAD)
        optimizer.step()
    if use_ema:
        ema_model = ModelEMA(model, decay=model_ema_decay)
        ema_model.update(model)
    else:
        ema_model = None
    test_acc = test(model, test_loader, DEVICE)
    if test_acc > Best_ACC:
        Best_ACC = test_acc
        save_checkpoint({
            'epoch': epoch,
            'state_dict': model.state_dict(),
            'optimizer': optimizer.state_dict(),
            'Best_ACC': Best_ACC,
        }, is_best=True)

解释一下这段代码：class FourierUnit(nn.Module): def __init__(self, in_channels, out_channels, groups=1): # bn_layer not used super(FourierUnit, self).__init__() self.groups = groups self.conv_layer = torch.nn.Conv2d(in_channels=in_channels * 2, out_channels=out_channels * 2, kernel_size=1, stride=1, padding=0, groups=self.groups, bias=False) self.bn = torch.nn.BatchNorm2d(out_channels * 2) self.relu = torch.nn.ReLU(inplace=True) self.gamma = nn.Parameter(torch.zeros(1)) self.gnconv = gnconv(out_channels * 2) def forward(self, x): batch, c, h, w = x.size() r_size = x.size() # (batch, c, h, w/2+1, 2) ffted = torch.fft.rfftn(x,s=(h,w),dim=(2,3),norm='ortho') ffted = torch.cat([ffted.real,ffted.imag],dim=1) ffted = self.conv_layer(ffted) # (batch, c*2, h, w/2+1) #ffted = self.gnconv(self.conv_layer(ffted)) ffted = self.relu(self.bn(ffted)) ffted = torch.tensor_split(ffted,2,dim=1) ffted = torch.complex(ffted[0],ffted[1]) output = torch.fft.irfftn(ffted,s=(h,w),dim=(2,3),norm='ortho') output = self.gamma * output + x return output

这段代码定义了一个名为 FourierUnit 的 PyTorch 模块，它实现了一个基于傅里叶变换的卷积层。

在 __init__ 方法中，模块接受三个参数：输入通道数 in_channels、输出通道数 out_channels 和分组数 groups。它首先调用父类的构造函数来初始化模块，然后设置一些属性，包括 groups、卷积层 conv_layer、批归一化层 bn、ReLU 激活函数 relu、可学习的参数 gamma，以及一个 gnconv 函数。

在 forward 方法中，模块接受输入张量 x，它的形状为 (batch, c, h, w)。模块首先计算输入张量的傅里叶变换，然后将实部和虚部拼接在一起，将得到的张量作为输入传递给卷积层 conv_layer。卷积层的输出形状为 (batch, c*2, h, w/2+1)。接着将其经过批归一化层和 ReLU 激活函数，然后将其拆分为实部和虚部，得到复数张量 ffted。最后，模块将 ffted 反傅里叶变换回时域，与输入张量相加得到输出张量 output。

这个模块的作用是在卷积层前添加一个傅里叶变换，以提取输入张量的频域信息，从而增强模型的特征提取能力。