Tips for LaTeX specific to mathematical typesetting. See also Chris Cheung’s list.

## Spacing and line breaking

Weird in maths.
The breqn package position paper explains many of the issues.
NB: the solutions that actually work in the javascript-backed LaTeX maths are `multline`

(nb only one `i`

) and `split`

environments, so in practice I use those to ensure cross-compatibility of copy-pasta.

## Opt-in equation numbering: `\numberthis`

The latex macro `\numberthis`

is satisfying.
Thanks Russell Tsuchida for showing it to me.
It allows me to number *only* needed lines in multi-line equations.
The macro goes like this:

`\newcommand\numberthis{\addtocounter{equation}{1}\tag{\theequation}}`

A minimal example in context:

```
\documentclass{article}
\usepackage{amsmath}
\newcommand\numberthis{\addtocounter{equation}{1}\tag{\theequation}}
\begin{document}
\begin{align*}
a &=b \\
&=c \numberthis \label{eqn}
\end{align*}
Equation \eqref{eqn} shows that $a=c$.
\begin{equation}
d = e
\end{equation}
\end{document}
```

## Math size

I forget this all the time. Explained by overleaf, Math font size ordering is

```
\displaystyle % Size for equations in display mode
\textstyle % Size for equations in text mode
\scriptstyle % Size for first sub/superscripts
\scriptscriptstyle % Size for subsequent sub/superscripts
```

## Arrays

There is an `array`

environment which is good for typesetting equations, but it is too verbose for typesetting arrays of other things like numbers.

Use `amsmath`

matrix for that, e.g.

```
\begin{pmatrix}
1 & 2 & 3\\
a & b & c
\end{pmatrix}
```

## Underbraces

If we want a brace underneath part of an equation, `amsmath`

provides `underbrace`

.

```
\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\begin{document}
\[
\underbrace{u'-P(x)u^2-Q(x)u-R(x)}_{\text{=0, since~$u$ is a particular solution.}}
\]
\end{document}
```

## Defining new operators

Without Limits i.e. limits on the side, \({\mathop{\mathrm{arg\,max}}\nolimits}_{x\to\infty} x\). Plain style (works everywhere including old MathJax):

`\newcommand{\sech}{\mathop{\mathrm{sech}}\nolimits}`

`amsmath`

style (works in AMSMath environments):

`\DeclareMathOperator{\sech}{sech}`

If we want limits underneath (Does not seem to display correctly on this blog so we will have to use our imaginations)

Vanilla:

`\newcommand{\sech}{\mathop{\mathrm sech}\limits}`

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