文档:https://wenku.baidu.com/view/55c029ab5122aaea998fcc22bcd126fff7055db6.html
视频:https://www.bilibili.com/video/BV1k7411w7Qr?p=1
正交多项式:https://wenku.baidu.com/view/5828796b03d276a20029bd64783e0912a3167c54.html