Write LaTeX Equations in Jekyll Using MathJax & Kramdown


What is MathJax

MathJax is a javascript library that uses the TeX algorithms and fonts to display math formulas on HTML pages. It allows for very fine-grained configuration, is widely used and works on all modern browsers.

This engine marks up math formulas with HTML <script type="math/tex"> tags that MathJax understands. The only other thing to do is to include the MathJax library itself on the HTML page.

Choose Markdown converter

Kramdown, a fast, pure-Ruby Markdown-superset converter, has built-in support for block and span-level mathematics written in \(\LaTeX\). What’s more, for Jekyll sites hosted on GitHub Pages, only the kramdown engine is supported.

If you are using other Markdown converter, like redcarpet, you need to change to markdown: kramdown in your _config.yml file.

Note that kramdown does not ship with the MathJax library and that therefore the “default” template does not include a link to it! we need to add a link to MathJax to our page.

Implement MathJax with Jekyll

MathJax provides varies kinds of plugins for different websites and frameworks, like WordPress. Check MathJax In Use and Using MathJax in popular web platforms to learn more.

To get MathJax support, add the lines to your theme layouts:

<!-- Mathjax Support -->
<script type="text/javascript" async

either just before the </head> tag in your theme file, or at the end of the file if it contains no </head>.

As for my site, you can find the above lines in /_includes/head.html.

Note that this will enable MathJax for your current theme/template only. If you change themes or update your theme, you will have to repeat these steps.

Math syntax in Kramdown

Note that this syntax feature is not part of the original Markdown syntax.

The default math delimiters are $$...$$ and \[...\] for displayed mathematics, and \(...\) for in-line mathematics.

Note in particular that the $...$ in-line delimiters are not used by default. Since dollar signs appear too often in non-mathematical settings.

The following kramdown fragment:

  & \phi(x,y) = \phi \left(\sum_{i=1}^n x_ie_i, \sum_{j=1}^n y_je_j \right)
  = \sum_{i=1}^n \sum_{j=1}^n x_i y_j \phi(e_i, e_j) = \\
  & (x_1, \ldots, x_n) \left( \begin{array}{ccc}
      \phi(e_1, e_1) & \cdots & \phi(e_1, e_n) \\
      \vdots & \ddots & \vdots \\
      \phi(e_n, e_1) & \cdots & \phi(e_n, e_n)
    \end{array} \right)
  \left( \begin{array}{c}
      y_1 \\
      \vdots \\
    \end{array} \right)

will render as

\[\begin{align*} & \phi(x,y) = \phi \left(\sum_{i=1}^n x_ie_i, \sum_{j=1}^n y_je_j \right) = \sum_{i=1}^n \sum_{j=1}^n x_i y_j \phi(e_i, e_j) = \\ & (x_1, \ldots, x_n) \left( \begin{array}{ccc} \phi(e_1, e_1) & \cdots & \phi(e_1, e_n) \\ \vdots & \ddots & \vdots \\ \phi(e_n, e_1) & \cdots & \phi(e_n, e_n) \end{array} \right) \left( \begin{array}{c} y_1 \\ \vdots \\ y_n \end{array} \right) \end{align*}\]

Note that LaTeX code that uses the pipe symbol | in inline math statements may lead to a line being recognized as a table line. This problem can be avoided by using the \vert command instead of |

If you have a paragraph that looks like a math block but should actually be a paragraph with just an inline math statement, you need to escape the first dollar sign:

The following is a math block:$$ 5 + 5 $$

But next comes a paragraph with an inline math statement:\$$ 5 + 5 $$

will render as

The following is a math block:\(5 + 5\)

But next comes a paragraph with an inline math statement:$$ 5 + 5 $$

If you don’t even want the inline math statement, escape the first two dollar signs:

$$ 5 + 5 $$

Further reading