Enable Math with your Kramdown or Jekyll blog

To enable Latex math, you need to first enable Mathjax.
This answer gives a solution by adding js.

<script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>

Particular for me, since I am using Jekyll theme Minimal-Mistakes, this doc instructs me to add a line into _config.yaml as such:

head_scripts:
  - http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML

There are two major approach of adding Latex.

1. block
   when there are lines of latex inside $$…$$, or there are blank lines before and after the two $$.
2. inline
   when the two $$ are used inline.

When there happens to be blank lines before and after the two $$, and you happens to want to use the inline version, write \$$…$$.

reference: a post, the doc.