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Math Equations

Settings

next/_config.yml
# Math Formulas Render Support
math:
# Default (false) will load mathjax / katex script on demand.
# That is it only render those page which has `mathjax: true` in front-matter.
# If you set it to true, it will load mathjax / katex srcipt EVERY PAGE.
every_page: false

mathjax:
enable: true
# Available values: none | ams | all
tags: none

katex:
enable: false
# See: https://github.com/KaTeX/KaTeX/tree/master/contrib/copy-tex
copy_tex: false

The every_page option controls whether to render Math Equations every page.

  • false → Equations will be processed on demand. It will only render those posts which have mathjax: true in their front-matter.
  • true → Equations will be processed on every page. Even if they not exists on one or another page.

Examples with every_page: false option

  • This post will render the Math Equations

    ---
    title: Will Render Math
    mathjax: true
    ---
  • This post will NOT render the Math Equations

    ---
    title: Not Render Math
    mathjax: false
    ---
  • This post will NOT render the Math Equations either

    ---
    title: Not Render Math Either
    ---

The mathjax and katex options are used to set the rendering engine. Please read the detailed document below.

Render Engines

For now, NexT provides two rendering engines for displaying Math Equations: MathJax and KaTeX.

  • MathJax is a JavaScript display engine for mathematics that works in all browsers. It is highly modular on input and output. Use MathML, TeX, and ASCIImath as input and produce HTML+CSS, SVG, or MathML as output.
  • KaTeX is a faster math rendering engine compared to MathJax 3. And it could survive without JavaScript. But, for now KaTeX supports less features than MathJax. Here is a list of TeX functions supported by KaTeX.

Firstly, you need to choose a rendering engine and turn on enable for it in theme config file. Then you need to install the corresponding Hexo Renderer to fully support the display of Math Equations - Only turn on enable may not let you see the displayed equations correctly.

Renderer Choosing

If you use MathJax to render Math Equations, you can choose one of the Markdown renderers below:

  • hexo-renderer-pandoc

hexo-renderer-pandoc is recommended because it can handle mathematical formulas in markdown documents perfectly.

If you are using other renderers, such as hexo-renderer-marked, you need to be aware of the conflict between LaTeX and Markdown syntax. For example, an underscore (_) may be interpreted as the start of italic text in Markdown, or subscripted mark in TeX. To avoid syntax errors, please use escape characters (\_) instead:

-$\epsilon_0$
+$\epsilon\_0$
-\begin{eqnarray*}
+\begin{eqnarray\*}
-\\
+\\\\

Installation

  1. Firstly, set mathjax as rendering engine in theme config file.

    next/_config.yml
    math:
    ...
    mathjax:
    enable: true
  2. Then you need to uninstall the original renderer hexo-renderer-marked, and install hexo-renderer-pandoc:

    $ npm un hexo-renderer-marked
    $ npm i hexo-renderer-pandoc
  3. pandoc is required for hexo-renderer-pandoc, here's how to install pandoc.

Plugins

All extensions of MathJax are loaded automatically. For example, mhchem is a tool for writing beautiful chemical equations easily. It implements the \ce and \pu chemical equation macros of the LaTeX mhchem package. More information: MathJax/mhchem Manual.

Renderer Choosing

If you use KaTeX to render Math Equations, you can choose one of the Markdown renderers below:

  • hexo-renderer-markdown-it-plus
  • hexo-renderer-markdown-it

Installation

  1. Firstly, set katex as rendering engine in theme config file.

    next/_config.yml
    math:
    ...
    katex:
    enable: true
  2. Then you need to uninstall the original renderer hexo-renderer-marked and install one of the renderer plugins:

$ npm un hexo-renderer-marked
$ npm i hexo-renderer-markdown-it-plus
$ npm un hexo-renderer-marked
$ npm i hexo-renderer-markdown-it

If you use hexo-renderer-markdown-it, you also need to install markdown-it-katex:

$ npm i markdown-it-katex

And then in site config file you need to add markdown-it-katex as a plugin for hexo-renderer-markdown-it:

hexo/_config.yml
# config of hexo-renderer-markdown-it
markdown:
render:
html: true
xhtmlOut: false
breaks: true
linkify: true
typographer: true
quotes: '“”‘’'
plugins:
- markdown-it-katex

Plugins

Copy-tex extension for KaTeX modifes the copy/paste behavior in any browser supporting the Clipboard API so that, when selecting and copying whole KaTeX-rendered elements, the text content of the resulting clipboard renders KaTeX elements as their LaTeX source surrounded by specified delimiters. More information: Copy-tex extension.

next/_config.yml
math:
...
katex:
# See: https://github.com/KaTeX/KaTeX/tree/master/contrib/copy-tex
copy_tex: true

Known Issues

  1. Firstly, please check Common Issues of KaTeX.
  2. Displayed Math (i.e. $$...$$) needs to started with new clear line.
    In other words: you must not have any characters (except of whitespaces) before the opening $$ and after the ending $$ (comment #32).
  3. Don't support Unicode (comment #32).
  4. Inline Math (..$...$) must not have white spaces after the opening $ and before the ending $ (comment #32).
  5. If you use math in Heading (i.e. ## Heading).
    Then in corresponding TOC item it will show the related LaTeX code 3 times (comment #32).
  6. If you use math in your post's title, it will not be rendered (comment #32).

After setting up the math rendering engine or installing / uninstalling the Markdown renderer, please execute hexo clean. Run standard Hexo generate, deploy process or start the server to test whether the plugin is working properly:

$ hexo clean && hexo g -d
# or hexo clean && hexo s

Except for the required renderer, any other Hexo math plugins are unnecessary and there is no need to manually import any JS or CSS files. If you have installed plugins such as hexo-math or hexo-katex, they may conflict with the built-in rendering engine of NexT.

Examples

The following examples are rendered by mathjax engine.

Numbering and Referring Equations in MathJax

In NexT v6.3.0, we have added feature to automatic equation numbering with opportunity to make reference to that equations.

To enable this feature, you need to set mathjax.tags to ams in theme config file.

math:
mathjax:
enable: true
# Available values: none | ams | all
tags: ams

And to make the automatic equation numbering work, you have to wrap your LaTeX equations in equation environment. Using the plain old style (i.e., wrap an equation with two dollar signs in each side) will not work. How to refer to an equation? Just give a \label{} tag and then in your later text, use \ref{} or \eqref{} to refer it. Using \eqref{} is preferred since if you use \ref{}, there are no parentheses around the equation number. Below are some of the common scenarios for equation numbering.

Simple Equations

For simple equations, use the following form to give a tag,

$$\begin{equation} \label{eq1}
e=mc^2
\end{equation}$$

$$\begin{equation} \label{eq1}
e=mc^2
\end{equation}$$

Then, you can refer to this equation in your text easily by using something like:

The famous matter-energy equation $\eqref{eq1}$ proposed by Einstein...

The famous matter-energy equation $\eqref{eq1}$ proposed by Einstein...

Multi-line Equations

For multi-line equations, inside the equation environment, you can use the aligned environment to split it into multiple lines:

$$\begin{equation} \label{eq2}
\begin{aligned}
a &= b + c \\
&= d + e + f + g \\
&= h + i
\end{aligned}
\end{equation}$$

$$\begin{equation} \label{eq2}
\begin{aligned}
a &= b + c \\
&= d + e + f + g \\
&= h + i
\end{aligned}
\end{equation}$$

Equation $\eqref{eq2}$ is a multi-line equation.

Equation $\eqref{eq2}$ is a multi-line equation.

Multiple Aligned Equations

We can use align environment to align multiple equations. Each of these equations will get its own numbers.

$$\begin{align}
a &= b + c \label{eq3} \\
x &= yz \label{eq4} \\
l &= m - n \label{eq5}
\end{align}$$

$$\begin{align}
a &= b + c \label{eq3} \\
x &= yz \label{eq4} \\
l &= m - n \label{eq5}
\end{align}$$

There are three aligned equations: equation $\eqref{eq3}$, equation $\eqref{eq4}$ and equation $\eqref{eq5}$.

There are three aligned equations: equation $\eqref{eq3}$, equation $\eqref{eq4}$ and equation $\eqref{eq5}$.

Since align in and of itself is a complete equation environment (read here about the difference between aligned and align in LaTeX). You do not need to wrap it with equation environment.

Exclude Equations from Numbering

In the align environment, if you do not want to number one or some equations, just use \nonumber right behind these equations. Like the following:

$$\begin{align}
-4 + 5x &= 2 + y \nonumber \\
w + 2 &= -1 + w \\
ab &= cb
\end{align}$$

$$\begin{align}
-4 + 5x &= 2 + y \nonumber \\
w + 2 &= -1 + w \\
ab &= cb
\end{align}$$

Use \tag to Tag Equations

Sometimes, you want to use more «exotic» style to refer your equation. You can use \tag{} to achieve this. For example:

$$x+1\over\sqrt{1-x^2} \tag{i}\label{eq_tag}$$

$$x+1\over\sqrt{1-x^2} \tag{i}\label{eq_tag}$$

Equation $\eqref{eq_tag}$ use `\tag{}` instead of automatic numbering.

Equation $\eqref{eq_tag}$ use \tag{} instead of automatic numbering.