Using latex \newcommand with revealjs output

[martintburgess]

Thanks for all your work on quarto - it's awesome.

I am following the example here for including equations in a quarto document using the revealjs format.

When I knit the following .qmd file the first slide has no output but the second slide has the desired output. Is there a recommended way to add latex code/equations to revealjs presents? Happy to be pointed to other examples - haven't found any.

---
title: "mre"
format: 
  revealjs:
    self-contained-math: true
---

## With newcommand, no output

```{=tex}
\newcommand\muy{\mathrm{mu\_y}}
\begin{equation}
\muy
\end{equation}

Without newcommand, output generated

\begin{equation}
\mathrm{mu\_y}
\end{equation}

[mcanouil]

Reveal.js is HTML, thus it raw tex is ignored.
Equations are a bit different because they are the only LaTeX commands processed with JavaScript: webtex, gladtex, mathml, mathjax or katex¹.
To note, some of those tools have an extension mechanism that you can use, see #1620 (reply in thread) which uses a MathJax extension.

If you really want to use LaTeX, choose beamer, not Reveal.js: https://quarto.org/docs/presentations/beamer.html

Footnotes

1. https://quarto.org/docs/reference/formats/html.html#format-options ↩

[cderv]

@martintburgess

HTML math in revealjs will use MathJax. In MathJax, if support exist for a TeX command, then you can use it. It happens that \newcommand is one of them (http://docs.mathjax.org/en/latest/input/tex/extensions/newcommand.html)

However, you need to use Math environment, with $$

---
title: "mre"
format: 
  revealjs:
    self-contained-math: true
---

$$
\newcommand\muy{\mathrm{mu\_y}}
\begin{equation}
\muy
\end{equation}
$$

By using only Raw latex with ```{=tex} you are explicitly telling Pandoc that the content is raw LaTeX and should be ignored in HTML output then. HTML writer does an exception for raw LaTeX that start with a math environment, but in your case that is not the case as \newcommand is before. If you put it inside, MathJax should now how to handle it.

Example

---
title: "mre"
format: 
  revealjs:
    self-contained-math: true
---

```{=tex}
\begin{equation}
\newcommand\muy{\mathrm{mu\_y}}
\muy
\end{equation}
```

But this would work too

---
title: "mre"
format: 
  revealjs:
    self-contained-math: true
---

\begin{equation}
\newcommand\muy{\mathrm{mu\_y}}
\muy
\end{equation}

In Markdown using the $$ syntax is easier, also because some IDE (like RStudio visual editor) will help for preview I think.

Overall, Mathjax processing adds a layer that needs to be understood when some specific customization are desired.

Hope it helps understand

[cscheid]

Note that (as I learned yesterday from another quarto user), \newcommand does work. You just need to adjust your syntax:

---
format: revealjs
---

\newcommand\muy{\mu_y}

We use $\muy$ (@eq-muy) to denote the mean of the $y$ parameter:

$$\muy$$ {#eq-muy}

Specifically, I think the issue you're seeing (on top of raw latex not being emitted in html formats) is that in quarto, we typically don't use \begin{equation}, we use display math ($$) and regular crossreferences ({#eq-muy}).

If you're careful to use \newcommand outside math mode, then the markdown should be portable across formats. This way, you get the following slides by default:

while

$ quarto render test-muy.qmd --to pdf

generates this PDF output:

while

[cderv]

Wow cool ! Thanks @cscheid !
This is a Pandoc feature right ?

Or maybe just Mathjax in fact. Definition in one math block will be available to another block ? 🤔 That would explain.
Anyway, so cool! 🤯

[cscheid]

It's Pandoc - if you look at the generated HTML, it doesn't even have \newcommand. Pandoc is actually doing the macro replacement. Pretty incredible.

[cscheid]

(and thank you @eeholmes for that lesson!)

[cderv]

Wow indeed. Pretty incredible for sure ! And it seems it is there in Pandoc since a long time. Always happy to find unknown gems like that! 😄

[martintburgess]

Amazing, thank you to everyone who responded so quickly - I now how 4 different ways this will work (seems like my way was the only way that didn't 😅). But more importantly - I've learnt a tonne.