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Jack Douglas
We've got MathJax (sort of) working on Code Golf, but I hadn't quite anticipated what a huge and complex library it is.

We can stick with it, but if something simpler like KaTeX would suit just as well or very nearly as well, we should probably use that instead. I have no idea whether it would though, but presumably you do!

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* Update 26 Jan 2020: we have swapped out MathJax for KaTeX
* Update 28 Jan 2020: upgrading the KaTeX library to the latest release has fixed some of the issues [pointed out by](/codegolf?q=621#a691) @Bubbler
I had a look at KaTeX and I'm convinced that it is *plenty* powerful for our needs. The improved rendering speed is nice too.
Bubbler
I tried out some math expressions from my own SE posts. It looks like ~~some of the features are not correctly working,~~ and some are visually not pleasing to read.

* ~~\begin{gathered} ... \end{gathered} isn't working~~ (using aligned instead makes all lines aligned to the right.)

$$\begin{gathered} \text{byte count before zilde} + \text{byte count of single zilde} \times \text{length of zilde chain} \\ = 52 + 3 \times (72x^{12} + 101x^{11} + 108x^{10} + 108x^9 + 111x^8 + \\ 44x^7 + 32x^6 + 87x^5 + 111x^4 + 114x^3 + 108x^2 + 100x + 33) \end{gathered}$$

\begin{aligned} \text{byte count before zilde} + \text{byte count of single zilde} \times \text{length of zilde chain} \\ = 52 + 3 \times (72x^{12} + 101x^{11} + 108x^{10} + 108x^9 + 111x^8 + \\ 44x^7 + 32x^6 + 87x^5 + 111x^4 + 114x^3 + 108x^2 + 100x + 33) \end{aligned}

* Using lots of fractions/binomials inside a container (cases or matrix) makes them look cramped. **Edit:** Changed \tfrac and \tbinom to plain \frac and \binom. Looks like they're now correctly rendered small inside containers, but the cramped issue is still there.

\begin{aligned} X & = \text{uniform random value in } (0,1) \\ Y & = \begin{cases} X + \frac12, \quad X < \frac12 \\ X - \frac12, \quad X \geq \frac12 \end{cases} \\ Z & = \frac32 - (X + Y) \end{aligned}

$$\begin{bmatrix} \binom{1}{1} & \binom{1}{2} & \cdots & \binom{1}{n+m} \\ \binom{2}{1} & \binom{2}{2} & \cdots & \binom{2}{n+m} \\ \vdots & \vdots & \ddots & \vdots \\ \binom{n+m}{1} & \binom{n+m}{2} & \cdots & \binom{n+m}{n+m} \end{bmatrix} \begin{bmatrix} a_1 \\ a_2 \\ \vdots \\ a_{n+m} \end{bmatrix} = \begin{bmatrix} \binom{1}{n} \binom{1}{m} \\ \binom{2}{n} \binom{2}{m} \\ \vdots \\ \binom{n+m}{n} \binom{n+m}{m} \end{bmatrix} \Leftrightarrow Ba = v$$

**Edit:** The KaTeX [Commen Issues](https://katex.org/docs/issues.html) page says:

> When displaying fractions one above another in these vertical layouts there may not be enough space between rows for people who are used to MathJax's rendering.

Their recommended solution is:

> The distance between rows can be adjusted by using \\[0.1em] instead of the standard line separator distance.

The math below uses \\[0.2em] instead to emphasise the difference:

$$\begin{bmatrix} \binom{1}{1} & \binom{1}{2} & \cdots & \binom{1}{n+m} \\[0.2em] \binom{2}{1} & \binom{2}{2} & \cdots & \binom{2}{n+m} \\[0.2em] \vdots & \vdots & \ddots & \vdots \\[0.2em] \binom{n+m}{1} & \binom{n+m}{2} & \cdots & \binom{n+m}{n+m} \end{bmatrix} \begin{bmatrix} a_1 \\ a_2 \\ \vdots \\ a_{n+m} \end{bmatrix} = \begin{bmatrix} \binom{1}{n} \binom{1}{m} \\[0.2em] \binom{2}{n} \binom{2}{m} \\[0.2em] \vdots \\ \binom{n+m}{n} \binom{n+m}{m} \end{bmatrix} \Leftrightarrow Ba = v$$

* ~~\implies symbol isn't working.~~

$$M = \begin{pmatrix} a & b \\ c & d \end{pmatrix} \implies S^{-1}M = \begin{pmatrix} c & d \\ -a & -b \end{pmatrix}, T^{-1}M = \begin{pmatrix} a-c & b-d \\ c & d \end{pmatrix}$$

$$M = \begin{pmatrix} a & b \\ c & d \end{pmatrix} \Rightarrow S^{-1}M = \begin{pmatrix} c & d \\ -a & -b \end{pmatrix}, T^{-1}M = \begin{pmatrix} a-c & b-d \\ c & d \end{pmatrix}$$

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