One of the rewards of switching my website to [Jekyll](http://jekyllrb.com/) is the ability to support **MathJax**, which means I can write LaTeX-like equations that get nicely displayed in a web browser, like this one \$\sqrt{\frac{n!}{k!(n-k)!}} \$ or this one \$x^2 + y^2 = r^2 \$. ### What's MathJax? If you check MathJax website [(www.mathjax.org)](http://www.mathjax.org/) you'll see that it *is an open source JavaScript display engine for mathematics that works in all browsers*. ### How to implement MathJax with Jekyll I followed the instructions described by Dason Kurkiewicz for [using Jekyll and Mathjax](http://dasonk.github.io/blog/2012/10/09/Using-Jekyll-and-Mathjax/). Here are some important details. I had to modify the Ruby library for Markdown in my _config.yml file. Now I'm using redcarpet so the corresponding line in the configuration file is: markdown: redcarpet To load the MathJax javascript, I added the following lines in my layout post.html (located in my folder _layouts) {% highlight r %} {% endhighlight %} Of course you can choose a different file location in your jekyll layouts. Note that by default, the **tex2jax** preprocessor defines the LaTeX math delimiters, which are \$...\$ for in-line math, and \$...\$ for displayed equations. It also defines the TeX delimiters $$...$$ for displayed equations, but it does not define $...$ as in-line math delimiters. To enable in-line math delimiter with $...$, please use the following configuration: {% highlight r %} {% endhighlight %} ### A Couple of Examples Here's a short list of examples. To know more about the details behind MathJax, you can always checked the provided documentation available at [http://docs.mathjax.org/en/latest/](http://docs.mathjax.org/en/latest/) Let's try a first example. Here's a dummy equation: $$a^2 + b^2 = c^2$$ How do you write such expression? Very simple: using **double dollar** signs {% highlight r %} $$a^2 + b^2 = c^2$$ {% endhighlight %} To display inline math use \$... \$ like this \$sin(x^2) \$ which gets rendered as \$sin(x^2) \$ Here's another example using type \mathsf {% highlight r %} $$\mathsf{Data = PCs} \times \mathsf{Loadings}$$ {% endhighlight %} which gets displayed as $$\mathsf{Data = PCs} \times \mathsf{Loadings}$$ Or even better: {% highlight r %} \$\mathbf{X} = \mathbf{Z} \mathbf{P^\mathsf{T}} \$ {% endhighlight %} is displayed as \$\mathbf{X} = \mathbf{Z} \mathbf{P^\mathsf{T}} \$ If you want to use subscripts like this \$\mathbf{X}\_{n,p} \$ you need to scape the underscores with a backslash like so  \mathbf{X}\_{n,p} : {% highlight r %} $$\mathbf{X}\_{n,p} = \mathbf{A}\_{n,k} \mathbf{B}\_{k,p}$$ {% endhighlight %} will be displayed as \$\mathbf{X}\_{n,p} = \mathbf{A}\_{n,k} \mathbf{B}\_{k,p} \$