Simple bradley terry model in pytorch
Wiki: https://en.wikipedia.org/wiki/Bradley%E2%80%93Terry_model
Example1: https://baike.baidu.com/item/Bradley-Terry%20%E6%A8%A1%E5%9E%8B/24209136
Example2: https://homepage.divms.uiowa.edu/~luke/xls/glim/glim/node8.html