Defining LaTeX commands for HTML and PDF rendering

[dmbates]

First let me again express my thanks for quarto and the skill and dedication of its developers. It has made my life a lot easier.

In working on a book at the repository https://github.com/JuliaMixedModels/EmbraceUncertainty I have been able to create HTML output but have problems with PDF related to LaTeX macros. An attempt to render the first chapter (intro.qmd) to PDF ends with

running xelatex - 1
  This is XeTeX, Version 3.141592653-2.6-0.999994 (TeX Live 2022) (preloaded format=xelatex)
   restricted \write18 enabled.
  entering extended mode
  
updating tlmgr

updating existing packages

compilation failed- error
Undefined control sequence.
l.362 represented by the random variable \(\mcY
                                               \). (We use upper-case 

At the beginning of intro.qmd \mcY is defined as

\newcommand\mcY{{\mathcal{Y}}}

and rendering to HTML is quite happy with that definition.

I can't decide why the HTML rendering picks up this definition but the PDF doesn't. (I am using TinyTeX installed through quarto tools.)

If someone could point me in the right direction I am happy to do more debugging myself or create an MWE (you don't want to mess around with installing Julia and Julia packages and Jupyter, etc., just to debug this.) It's about time that I did more exploration of saving intermediates, freezing Jupyter results, etc. I just don't quite know where to start.

[cscheid]

What I think is happening here is that latex doesn't like \newcommand in math mode, while MathJax probably accommodates that (for obvious reasons.)

You can see roughly what's going on by this minimal example:

---
title: Test
---

::: {.hidden}
$$
\newcommand\mcy{{\mathcal{y}}}
$$
:::

Will this work? $\mcy = 3$.

Now, let's try to render this to a latex document (not a pdf document):

$ quarto render newcommand-test.qmd --to latex

Note that the output here is now a latex file, which helps with debugging error messages:

pandoc
  to: latex
  output-file: newcommand-test.tex
  standalone: true
  pdf-engine: xelatex
  variables:
    graphics: true
    tables: true
  default-image-extension: pdf

metadata
  documentclass: scrartcl
  classoption:
    - DIV=11
    - numbers=noendperiod
  papersize: letter
  header-includes:
    - '\KOMAoption{captions}{tableheading}'
  block-headings: true
  title: Test

Output created: newcommand-test.tex

Now look at the end of this file:

$ tail newcommand-test.tex

\[
\newcommand\mcy{{\mathcal{y}}}
\]

Will this work? \(\mcy = 3\).

\end{document}

So one way to make this work is to use our format-specific hiding code:

---
title: Test
---

::: {.content-hidden unless-format="html"}
$$
\newcommand\mcy{{\mathcal{y}}}
$$
:::

::: {.content-hidden unless-format="pdf"}
```{=latex}
\newcommand\mcy{{\mathcal{y}}}
```
:::

Will this work? $\mcy = 3$.

This will generate the content you're expecting.

[dmbates]

Thank you, @cscheid . I will try that out and report back.

[dmbates]

Worked fine. Thank you.

[eeholmes]

This worked fine for me to both PDF and html. I am also using TinyTex. Note since the command is latex not math, I don't have it defined in a math environment.

---
title: Test
format:
  pdf: 
    documentclass: scrartcl
  html: default
---

\newcommand\mcy{{\mathcal{y}}}

Will this work? $\mcy = 3$.

[cscheid]

Whoa, I didn't know this actually works! @eeholmes: That's excellent, thank you! (And I help write quarto :))

I'm going to investigate how this works and report here for those interested.

The reason this is interesting is that this syntax should not work right away in HTML formats, because MathJax (the JS library we use to typeset latex equations) in principle only looks at code inside $. And, in fact, the HTML being processed by MathJax does not have the \newcommand line at all (!)

<main class="content" id="quarto-document-content">

<header id="title-block-header" class="quarto-title-block default">
  <div class="quarto-title"><h1 class="title">Test</h1></div>
  <div class="quarto-title-meta"></div>
</header>

<p>Will this work? <span class="math inline">\({\mathcal{y}}= 3\)</span>.</p>

</main>

So it must be that either our own postprocessors or Pandoc are interpreting the \newcommand line and actually substituting it in the markdown, ahead of HTML generation. Slick!

[eeholmes]

I think Pandoc is doing it. I have written in LaTeX for years with Sweave then RMarkdown. I just write LaTeX as normal and let Pandoc do its thing. I literally make no changes to my '*.tex' files except to remove the header and \begin{document} \end{document} parts. Everything else just works.

I don't know when HTML output started "just working". After PDF, but I don't recall when.

Lol. It must have been fixed after 2015, because in 2015, I was still fighting Pandoc and Mathjax when outputting to html and pdf. https://stackoverflow.com/questions/33226675/how-to-get-bm-to-work-in-an-r-markdown-to-html-file/43595791#43595791

[kjohnsen]

This doesn't work when you have arguments in your macro, unfortunately, e.g.

 \newcommand\mini #1{ \underset{#1} {\text{minimize}} }

This worked in the hidden math div for HTML though. I guess I need to do the hidden div+hidden code block strategy to get this to work in both HTML and LaTeX?

[evangorstein]

@kjohnsen , If you change what you wrote slightly to

\newcommand{\mini}[1]{ \underset{#1} {\text{minimize}} }

you can later write
$mini{x}$

and it renders properly in both pdf and HTML for me.
I think Pandoc makes this work for both pdf and HTML--check out https://pandoc.org/MANUAL.html#latex-macros