# $\LaTeX$ Syntax

The following section describes how to add equations written using $\LaTeX$ to your documentation.

## Escaping Characters in Docstrings

Since some characters used in $\LaTeX$ syntax, such as `$`

and `\`

, are treated differently in docstrings. They need to be escaped using a `\`

character as in the following example:

```
"""
Here's some inline maths: ``\\sqrt[n]{1 + x + x^2 + \\ldots}``.
Here's an equation:
``\\frac{n!}{k!(n - k)!} = \\binom{n}{k}``
This is the binomial coefficient.
"""
func(x) = # ...
```

Note that for equations on the manual pages (in `.md`

files) the escaping is not necessary. So, when moving equations between the manual and docstrings, the escaping `\`

characters have to the appropriately added or removed.

To avoid needing to escape the special characters in docstrings the `raw""`

string macro can be used, combined with `@doc`

:

```
@doc raw"""
Here's some inline maths: ``\sqrt[n]{1 + x + x^2 + \ldots}``.
Here's an equation:
``\frac{n!}{k!(n - k)!} = \binom{n}{k}``
This is the binomial coefficient.
"""
func(x) = # ...
```

A related issue is how to add dollar signs to a docstring. They need to be double-escaped as follows:

```
"""
The cost was \\\$1.
"""
```

## Inline Equations

`Here's some inline maths: ``\sqrt[n]{1 + x + x^2 + \ldots}``.`

which will be displayed as

Here's some inline maths: $\sqrt[n]{1 + x + x^2 + \ldots}$.

Similar to LaTeX, using `$`

and `$$`

to escape inline and display equations also works. However, doing so is deprecated and this functionality may be removed in a future release.

## Display Equations

```
Here's an equation:
```math
\frac{n!}{k!(n - k)!} = \binom{n}{k}
```
This is the binomial coefficient.
---
To write a system of equations, use the `aligned` environment:
```math
\begin{aligned}
\nabla\cdot\mathbf{E} &= 4 \pi \rho \\
\nabla\cdot\mathbf{B} &= 0 \\
\nabla\times\mathbf{E} &= - \frac{1}{c} \frac{\partial\mathbf{B}}{\partial t} \\
\nabla\times\mathbf{B} &= - \frac{1}{c} \left(4 \pi \mathbf{J} + \frac{\partial\mathbf{E}}{\partial t} \right)
\end{aligned}
```
These are Maxwell's equations.
```

which will be displayed as

Here's an equation:

\[\frac{n!}{k!(n - k)!} = \binom{n}{k}\]

This is the binomial coefficient.

To write a system of equations, use the `aligned`

environment:

\[\begin{aligned} \nabla\cdot\mathbf{E} &= 4 \pi \rho \\ \nabla\cdot\mathbf{B} &= 0 \\ \nabla\times\mathbf{E} &= - \frac{1}{c} \frac{\partial\mathbf{B}}{\partial t} \\ \nabla\times\mathbf{B} &= - \frac{1}{c} \left(4 \pi \mathbf{J} + \frac{\partial\mathbf{E}}{\partial t} \right) \end{aligned}\]

These are Maxwell's equations.

## Printing LaTeX from Julia

To pretty-print LaTeX from Julia, overload `Base.show`

for the `MIME"text/latex"`

type. For example:

```
struct LaTeXEquation
content::String
end
function Base.show(io::IO, ::MIME"text/latex", x::LaTeXEquation)
# Wrap in $$ for display math printing
return print(io, "\$\$ " * x.content * " \$\$")
end
LaTeXEquation(raw"""
\left[\begin{array}{c}
x \\
y
\end{array}\right]
""")
```

\[ \left[\begin{array}{c} x \\ y \end{array}\right] \]

## Set math engine and define macros for LaTeX

The `mathengine`

argument to `Documenter.Writers.HTMLWriter.HTML`

allows the math rendering engine to be specified, supporting both MathJax and KaTeX (with the latter being the default).

Furthermore, you can also pass custom configuration to the rendering engine. E.g. to add global LaTeX command definitions, you can set `mathengine`

to:

```
mathengine = Documenter.MathJax(Dict(:TeX => Dict(
:equationNumbers => Dict(:autoNumber => "AMS"),
:Macros => Dict(
:ket => ["|#1\\rangle", 1],
:bra => ["\\langle#1|", 1],
),
)))
```

Or with MathJax v3, the physics package can be loaded:

```
mathengine = MathJax3(Dict(
:loader => Dict("load" => ["[tex]/physics"]),
:tex => Dict(
"inlineMath" => [["\$","\$"], ["\\(","\\)"]],
"tags" => "ams",
"packages" => ["base", "ams", "autoload", "physics"],
),
)),
```

`MathJax2`

, `MathJax3`

and `KaTeX`

are available types for `mathengine`

.