1.可用环境

torch==1.7.1+cu110
torchvision==0.8.2+cu110

2.错误环境遇到的问题

（1）情况一

torch==1.7.0+cu110
torchvision==0.8.0

训练yolov5时，训练就会开始报错：

return torch.ops.torchvision.nms(boxes, scores, iou_threshold)
RuntimeError: Could not run 'torchvision::nms' with arguments from the 'CUDA' backend. 'torchvision::nms' is only available for these backends: [CPU, BackendSelect, Named, AutogradOther, AutogradCPU, AutogradCUDA, AutogradXLA, Tracer, Autocast, Batched, VmapMode].

torchvision版本不对。 所以升级了torchvision的版本。进入到情况二。

（2）情况二

torch==1.7.0+cu110
torchvision==0.8.1

训练第一个epoch时，不出错，但是测试第一个epoch的时候，会报错：

"Couldn't load custom C++ ops. This can happen if your PyTorch and "
RuntimeError: Couldn't load custom C++ ops. This can happen if your PyTorch and torchvision versions are incompatible, or if you had errors while compiling torchvision from source. For further information on the compatible versions, check https://github.com/pytorch/vision#installation for the compatibility matrix. Please check your PyTorch version with torch.__version__ and your torchvision version with torchvision.__version__ and verify if they are compatible, and if not please reinstall torchvision so that it matches your PyTorch install.

torch版本不对。这个时候就要torch与torchvision对应的一起升级。

3.针对以上分析

找到了正确的环境：

torch==1.7.1+cu110
torchvision==0.8.2+cu110

安装：

pip install torch==1.7.1+cu110 -f https://download.pytorch.org/whl/torch_stable.html
pip install torchvision==0.8.2+cu110 -f https://download.pytorch.org/whl/torch_stable.html