协方差python实现，这个大佬讲的很详细，终于明白了，感谢，感谢。
https://blog.csdn.net/u012421852/article/details/80487521?utm_medium=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-1.channel_param&depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-1.channel_param
