# Contributing an article

If you’re writing an article for this blog, please follow these guidelines.

One of the rewards of switching my website to Jekyll 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) 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.

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 `page.html`

(located in my folder `_layouts`

)

Of course you can choose a different file location in your jekyll layouts.

### 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/

I’m assuming you are familiar with LaTeX. However, you should know that MathJax does not
have the exactly same behavior as LaTeX. 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. Fortunately,
you can change these predefined specifications if you want to do so.

Let’s try a first example. Here’s a dummy equation:

How do you write such expression? Very simple: using **double dollar** signs

To display inline math use `\\( ... \\)`

like this `\\( sin(x^2) \\)`

which gets
rendered as \( sin(x^2) \)

Here’s another example using type `\mathsf`

which gets displayed as

Or even better:

is displayed as

\[ \mathbf{X} = \mathbf{Z} \mathbf{P^\mathsf{T}} \]

## Important notes

### 1. Subscripts

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}`

:

will be displayed as

\[ \mathbf{X}_{n,p} = \mathbf{A}_{n,k} \mathbf{B}_{k,p} \]

### 2. vertical line

If you want to use vertical line `|`

, you also need to scape the underscores with a blackslash like so `\|`

will be displayed as

\[ ||A|| \]