PyTorch 卷积神经网络简介
Convents 就是从头开始构建 CNN 模型。网络架构将包含以下步骤的组合:
- Conv2d
- MaxPool2d
- 整流线性单元
- View
- 线性层
训练模型
训练模型与图像分类问题的过程相同。以下代码片段完成了在提供的数据集上训练模型的过程:
def fit(epoch,model,data_loader,phase = 'training',volatile = False): if phase == 'training': model.train() if phase == 'training': model.train() if phase == 'validation': model.eval() volatile=True running_loss = 0.0 running_correct = 0 for batch_idx , (data,target) in enumerate(data_loader): if is_cuda: data,target = data.cuda(),target.cuda() data , target = Variable(data,volatile),Variable(target) if phase == 'training': optimizer.zero_grad() output = model(data) loss = F.nll_loss(output,target) running_loss + = F.nll_loss(output,target,size_average = False).data[0] preds = output.data.max(dim = 1,keepdim = True)[1] running_correct + = preds.eq(target.data.view_as(preds)).cpu().sum() if phase == 'training': loss.backward() optimizer.step() loss = running_loss/len(data_loader.dataset) accuracy = 100. * running_correct/len(data_loader.dataset) print(f'{phase} loss is {loss:{5}.{2}} and {phase} accuracy is {running_correct}/{len(data_loader.dataset)}{accuracy:{return loss,accuracy}})
该方法包括用于训练和验证的不同逻辑。使用不同模式的主要原因有两个:
-
在训练模式下,dropout 会删除一定百分比的值,这在验证或测试阶段不应该发生。
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对于训练模式,我们计算梯度并更改模型的参数值,但在测试或验证阶段不需要反向传播。