R Markdown similar feature to “newcommand” in LaTe

问题:

Does R Markdown have a similar construct to LaTex's "newcommand"? I would like to be able to define things like \var to be \mathrm{Var} to avoid the extra typing in math mode. If not, what do people do to reduce repetition in typesetting equations in markdown?

回答1:

Use \newcommand{\var}{\mathrm{Var}} exactly like you would in LaTeX:

---
title: "Untitled"
author: "An Author"
date: "January 15, 2017"
output: html_document
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

\newcommand{\var}{\mathrm{Var}}

## R Markdown

This is an R Markdown document. $\var+2$ Markdown is a simple formatting syntax for 
authoring HTML, PDF, and MS Word documents. For more details on using R Markdown 
see <http://rmarkdown.rstudio.com>.

Note that in order for it to be processed correctly in the output, you'll have to use $...$.

回答2:

I had issues with the above solution when outputting as a beamer presentation, particularly when using the equation mode ($$.$$ rather than $.$). Putting the new commands in a separate file fixed the issue for me.

---
title: Title
author: Author
date: "8/22/2018"
output:
  beamer_presentation:
    includes:
      in_header: preamble.tex
---

Where preamble.tex contains your user defined command(s)

\newcommand{\var}{\mathrm{Var}}

Then you can use the command both inline ($\var$) and in equation mode ($$\var$$)

You can also put other stuff in preamble.tex like frame numbering, etc.

回答3:

To get around the requirement of \DeclareMathOperator needing to be in the preamble, use \operatorname:

\newcommand{\Var}{\operatorname{Var}}

$\Var(X)$

(\operatorname handles spacing better than \mathrm)

To use \newcommand properly in HTML output, your LaTeX should be in-line with single $ or in double $$. This applies to environments like \begin{align*} too.

---
title: "Test"
author: "qwr"
date: "January 22, 2019"
output: html_document
---

\newcommand{\Var}{\operatorname{Var}}

$\Var(X)$

$$
\begin{align*}
\Var[Y] &= x \\
&= 3
\end{align*}
$$