一文理解Ranking Loss/Margin Loss/Triplet Loss
https://zhuanlan.zhihu.com/p/158853633
https://gombru.github.io/2019/04/03/ranking_loss/
排序学习(learning to rank)中的ranknet pytorch简单实现
https://www.cnblogs.com/little-horse/p/10468311.html
