以下是ResNet18模型的具体代码实现,使用PyTorch框架:
import torch import torch.nn as nn class BasicBlock(nn.Module): expansion = 1 def __init__(self, in_channels, out_channels, stride=1, downsample=None): super(BasicBlock, self).__init__() self.conv1 = nn.Conv2d(in_channels, out_channels, kernel_size=3, stride=stride, padding=1, bias=False) self.bn1 = nn.BatchNorm2d(out_channels) self.relu = nn.ReLU(inplace=True) self.conv2 = nn.Conv2d(out_channels, out_channels, kernel_size=3, padding=1, bias=False) self.bn2 = nn.BatchNorm2d(out_channels) self.downsample = downsample def forward(self, x): identity = x out = self.conv1(x) out = self.bn1(out) out = self.relu(out) out = self.conv2(out) out = self.bn2(out) if self.downsample is not None: identity = self.downsample(x) out += identity out = self.relu(out) return out class <em>ResNet</em>18(nn.Module): def __init__(self, block, layers, num_classes=1000): super(<em>ResNet</em>18, self).__init__() self.in_channels = 64 self.conv1 = nn.Conv2d(3, 64, kernel_size=7, stride=2, padding=3, bias=False) self.bn1 = nn.BatchNorm2d(64) self.relu = nn.ReLU(inplace=True) self.maxpool = nn.MaxPool2d(kernel_size=3, stride=2, padding=1) self.layer1 = self.make_layer(block, 64, layers[0]) self.layer2 = self.make_layer(block, 128, layers[1], stride=2) self.layer3 = self.make_layer(block, 256, layers[2], stride=2) self.layer4 = self.make_layer(block, 512, layers[3], stride=2) self.avgpool = nn.AdaptiveAvgPool2d((1, 1)) self.fc = nn.Linear(512 * block.expansion, num_classes) def make_layer(self, block, out_channels, blocks, stride=1): downsample = None if stride != 1 or self.in_channels != out_channels * block.expansion: downsample = nn.Sequential( nn.Conv2d(self.in_channels, out_channels * block.expansion, kernel_size=1, stride=stride, bias=False), nn.BatchNorm2d(out_channels * block.expansion) ) layers = [] layers.append(block(self.in_channels, out_channels, stride, downsample)) self.in_channels = out_channels * block.expansion for _ in range(1, blocks): layers.append(block(self.in_channels, out_channels)) return nn.Sequential(*layers) def forward(self, x): x = self.conv1(x) x = self.bn1(x) x = self.relu(x) x = self.maxpool(x) x = self.layer1(x) x = self.layer2(x) x = self.layer3(x) x = self.layer4(x) x = self.avgpool(x) x = torch.flatten(x, 1) x = self.fc(x) return x def <em>resnet</em>18(num_classes=1000): return <em>ResNet</em>18(BasicBlock, [2, 2, 2, 2], num_classes=num_classes)
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其中,BasicBlock定义了ResNet18中的基本块,<em>ResNet</em>18定义了ResNet18模型,最后的<em>resnet</em>18函数用于创建ResNet18模型,可以根据需要传入类别数目。

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