1. Personal website of Teacher Huang Zhenghua of Wuhan University
[Introduction] There are pdf downloads related to matrix theory, probability theory, advanced mathematics, linear algebra, discrete mathematics, and Latex tutorials.
http://aff.whu.edu.cn/huangzh/
2. Baidu Library-Linear Algebra
[Introduction] The summary is concise and clear, suitable for students who have just completed the online substitute course for examination review.
https://wenku.baidu.com/view/33ce6834a32d7375a41780f7.html
If there is a website that can be as easy to use as mathtype+word, so that you can view and summarize the principles of mathematics in real time. (The preliminary idea can be done like this: the user interface is used for imaging with Mathtype word, and the underlying implementation uses makedown or Latex)