refer to https://zhuanlan.zhihu.com/p/31886934
video https://study.163.com/course/courseLearn.htm?courseId=1003590004&share=1&shareId=1024261853#/learn/video?lessonId=1043875199&courseId=1003590004
SVM 三境界 https://blog.csdn.net/v_july_v/article/details/7624837
