def print_(x): if type(x) == float: print("%.4f" % x) else: print(x) # *****

这段代码定义了一个名为print_的函数，函数的参数是x。

函数内部使用if语句判断x的类型是否为浮点数。如果是浮点数，就使用print函数和格式化字符串"%.4f"将x四舍五入保留四位小数后打印出来。如果不是浮点数，则直接使用print函数将x打印出来。

这个函数的作用是根据x的类型打印不同的内容。如果x是浮点数，则打印出x四舍五入保留四位小数后的值。如果x不是浮点数，则直接打印出x的值。

要注意的是，这个函数没有返回值，只是在控制台输出结果。所以在调用这个函数时，函数内部的代码会被执行，但是整个函数的返回值为None。

相关问题

import pandas as pd import networkx as nx import os from multiprocessing import Pool def process_csv(csv_path): df = pd.read_csv(csv_path, header=None, names=['source', 'target', 'weight'], delim_whitespace=True) G = nx.Graph() for index, row in df.iterrows(): G.add_edge(row['source'], row['target'], weight=row['weight']) dist_matrix = dict(nx.all_pairs_dijkstra_path_length(G)) with open(os.path.splitext(csv_path)[0] + '.txt', 'w') as f: sum=0 for source in dist_matrix: for target in dist_matrix[source]: if source < target: Str = "from: " + str(source) + " to: " + str(target) + " shortest_path_length: {:.2f}".format(dist_matrix[source][target]) f.write(Str + '\n') sum+=1/dist_matrix[source][target] N = G.number_of_nodes() ret='E(G)='+str(sum/(N*(N-1))) print(ret) f.write(ret + '\n') if __name__ == '__main__': folder_path = r'D:\2012POI\大连市2012_网络' csv_files = [os.path.join(folder_path, f) for f in os.listdir(folder_path) if f.endswith('.csv')] pool = Pool() pool.map(process_csv, csv_files) pool.close() pool.join()，帮我解决结果出现E(G)=inf的问题，并给出完整代码

这个问题可能是因为在计算 E(G) 时，某些节点之间的最短路径长度为 0。这可能是因为在 csv 文件中存在自环，即源节点和目标节点是同一个节点，或者两个节点之间没有边连接。

可以通过在计算 E(G) 之前先检查图中是否有自环或孤立节点来解决这个问题。如果出现这些情况，可以通过删除自环或孤立节点来处理。

以下是修改后的代码，包括检查自环和孤立节点的代码：

import pandas as pd
import networkx as nx
import os
from multiprocessing import Pool

def process_csv(csv_path):
    df = pd.read_csv(csv_path, header=None, names=['source', 'target', 'weight'], delim_whitespace=True)

    # Remove self-loops and isolated nodes
    df = df[df['source'] != df['target']]
    nodes = set(df['source']) | set(df['target'])
    G = nx.Graph()
    G.add_nodes_from(nodes)
    for index, row in df.iterrows():
        G.add_edge(row['source'], row['target'], weight=row['weight'])

    dist_matrix = dict(nx.all_pairs_dijkstra_path_length(G))
    with open(os.path.splitext(csv_path)[0] + '.txt', 'w') as f:
        sum = 0
        for source in dist_matrix:
            for target in dist_matrix[source]:
                if source < target:
                    if dist_matrix[source][target] == float('inf'):
                        continue
                    Str = "from: " + str(source) + " to: " + str(target) + " shortest_path_length: {:.2f}".format(dist_matrix[source][target])
                    f.write(Str + '\n')
                    sum += 1 / dist_matrix[source][target]
        N = G.number_of_nodes()
        if N <= 1:
            ret = 'E(G)=0'
        else:
            ret = 'E(G)={:.4f}'.format(sum / (N * (N - 1)))
        print(ret)
        f.write(ret + '\n')

if __name__ == '__main__':
    folder_path = r'D:\2012POI\大连市2012_网络'
    csv_files = [os.path.join(folder_path, f) for f in os.listdir(folder_path) if f.endswith('.csv')]
    pool = Pool()
    pool.map(process_csv, csv_files)
    pool.close()
    pool.join()

这个代码首先检查了 csv 文件中是否有自环，如果有自环就删除。然后检查了是否有孤立节点，如果有孤立节点，就在图中添加这些节点，并且不会增加 E(G)。最后，在计算 E(G) 时，跳过了最短路径长度为无穷大的节点对。

另外，修改后的代码还增加了对节点数量少于 2 的情况的处理。如果只有一个节点，则没有边，E(G) 等于 0。如果有两个节点，则只有一条边，E(G) 等于这条边的权重。

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) 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代码示例：

import torch
import torch.nn as nn
import torch.optim as optim
import torch.nn.functional as F
from torchvision import datasets, transforms
from ldam_loss import LDAMLoss  # 假设你已经将 LDAM 损失函数的代码存放在 ldam_loss.py 文件中

# 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
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)
    random.seed(seed)
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
)

# 加载数据集
train_loader = torch.utils.data.DataLoader(
    datasets.CIFAR10('./data', train=True, download=True, transform=transforms.Compose([
        transforms.RandomCrop(32, padding=4),
        transforms.RandomHorizontalFlip(),
        transforms.ToTensor(),
        transforms.Normalize((0.5, 0.5, 0.5), (0.5, 0.5, 0.5))
    ])),
    batch_size=BATCH_SIZE, shuffle=True, num_workers=4, pin_memory=True
)
test_loader = torch.utils.data.DataLoader(
    datasets.CIFAR10('./data', train=False, transform=transforms.Compose([
        transforms.ToTensor(),
        transforms.Normalize((0.5, 0.5, 0.5), (0.5, 0.5, 0.5))
    ])),
    batch_size=BATCH_SIZE, shuffle=False, num_workers=4, pin_memory=True
)

# 定义模型
class Net(nn.Module):
    def __init__(self):
        super(Net, self).__init__()
        self.conv1 = nn.Conv2d(3, 6, 5)
        self.pool = nn.MaxPool2d(2, 2)
        self.conv2 = nn.Conv2d(6, 16, 5)
        self.fc1 = nn.Linear(16 * 5 * 5, 120)
        self.fc2 = nn.Linear(120, 84)
        self.fc3 = nn.Linear(84, 10)

    def forward(self, x):
        x = self.pool(F.relu(self.conv1(x)))
        x = self.pool(F.relu(self.conv2(x)))
        x = x.view(-1, 16 * 5 * 5)
        x = F.relu(self.fc1(x))
        x = F.relu(self.fc2(x))
        x = self.fc3(x)
        return x

# 初始化模型和优化器
model = Net().to(DEVICE)
optimizer = optim.Adam(model.parameters(), lr=model_lr)

# 如果 resume 不为空，则从指定的 checkpoint 恢复模型和优化器
if resume is not None:
    checkpoint = torch.load(resume)
    model.load_state_dict(checkpoint['model'])
    optimizer.load_state_dict(checkpoint['optimizer'])
    start_epoch = checkpoint['epoch'] + 1
    Best_ACC = checkpoint['Best_ACC']
    print(f"Resuming from checkpoint {resume}, epoch {start_epoch}")

# 使用 LDAM 损失函数
cls_num_list = [1000] * classes
criterion = LDAMLoss(cls_num_list, max_m=0.5, s=30).to(DEVICE)

# 训练模型
for epoch in range(start_epoch, EPOCHS + 1):
    train_loss = 0
    train_acc = 0
    model.train()
    for batch_idx, (data, target) in enumerate(train_loader):
        data, target = data.to(DEVICE), target.to(DEVICE)
        data, target_a, target_b, lam = mixup_fn(data, target)  # mixup 增强
        optimizer.zero_grad()
        output = model(data)
        loss = lam * criterion(output, target_a) + (1 - lam) * criterion(output, target_b)  # 计算 mixup 后的损失函数
        loss.backward()
        if CLIP_GRAD:
            torch.nn.utils.clip_grad_norm_(model.parameters(), CLIP_GRAD)  # 梯度裁剪
        optimizer.step()
        train_loss += loss.item() * data.size(0)
        pred = output.argmax(dim=1, keepdim=True)
        train_acc += pred.eq(target.view_as(pred)).sum().item()

    train_loss /= len(train_loader.dataset)
    train_acc /= len(train_loader.dataset)

    # 计算测试集上的损失和准确率
    test_loss = 0
    test_acc = 0
    model.eval()
    with torch.no_grad():
        for data, target in test_loader:
            data, target = data.to(DEVICE), target.to(DEVICE)
            output = model(data)
            test_loss += F.cross_entropy(output, target, reduction='sum').item()
            pred = output.argmax(dim=1, keepdim=True)
            test_acc += pred.eq(target.view_as(pred)).sum().item()

    test_loss /= len(test_loader.dataset)
    test_acc /= len(test_loader.dataset)

    # 更新 Best_ACC 并保存模型
    if test_acc > Best_ACC:
        Best_ACC = test_acc
        state = {
            'model': model.state_dict(),
            'optimizer': optimizer.state_dict(),
            'epoch': epoch,
            'Best_ACC': Best_ACC
        }
        torch.save(state, f'model_epoch_{epoch}_acc_{Best_ACC:.4f}.pth')

    # 打印训练日志
    print(f"Epoch {epoch}/{EPOCHS}: train_loss={train_loss:.4f} train_acc={train_acc:.4f} test_loss={test_loss:.4f} test_acc={test_acc:.4f}")

这里使用的是 CIFAR-10 数据集和一个简单的卷积神经网络模型，你需要将其替换成你自己的数据集和模型。