学习曲线和决策边界的绘制
https://blog.csdn.net/qq_36523839/article/details/82556932
https://blog.csdn.net/ChenVast/article/details/79257387
https://blog.csdn.net/geduo_feng/article/details/79547554
https://blog.csdn.net/weixin_39561100/article/details/79464134
颜色填充(fill & fill_between)
https://blog.csdn.net/you_are_my_dream/article/details/53457960