PyTorch里的requires_grad、volatile及no_grad
https://www.jianshu.com/p/ba203f4bcf4b
PyTorch简明笔记[2]-Tensor的自动求导(AoutoGrad) 【对于backward讲的挺好】
https://www.jianshu.com/p/a105858567df
扩展autograd
https://blog.youkuaiyun.com/tsq292978891/article/details/79364140