https: gnuplot

https://blog.csdn.net/xinming_365/article/details/11083126
https://baijiahao.baidu.com/s?id=1721462807761589396&wfr=spider&for=pc
https://www.cnblogs.com/zhangjing327/p/3524106.html
https://zhuanlan.zhihu.com/p/32237846
https://blog.csdn.net/timchen525/article/details/75331121
https://blog.csdn.net/weixin_38468077/article/details/101069365?spm=1001.2101.3001.6650.4&utm_medium=distribute.pc_relevant.none-task-blog-2%7Edefault%7ECTRLIST%7ERate-4.pc_relevant_default&depth_1-utm_source=distribute.pc_relevant.none-task-blog-2%7Edefault%7ECTRLIST%7ERate-4.pc_relevant_default&utm_relevant_index=9
https://blog.csdn.net/liyuanbhu/article/details/8502383
https://blog.csdn.net/qq_33523925/article/details/87936254
https://www.cnblogs.com/jhcelue/p/6897249.html

 splot x**+y**2