https://blog.csdn.net/qq_40765537/article/details/106865141?utm_medium=distribute.pc_relevant.none-task-blog-baidujs_baidulandingword-6&spm=1001.2101.3001.4242
https://blog.csdn.net/snail9610/article/details/105925426?utm_medium=distribute.pc_relevant.none-task-blog-BlogCommendFromBaidu-1.not_use_machine_learn_pai&depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromBaidu-1.not_use_machine_learn_pai
思考：K折交叉验证，和留一交叉验证的区别，就是K_CV中每组里包含大于等于1个样本？而留一是每组只有一个样本？