[Tex/LaTex] A short hyphen in a math formula

Question

In a LyX math formula, I want to write something like "r-number". However, the usual dash looks too long (like a minus sign). I am looking for a short, possibly upper hyphen. I couldn't find it in the lists of symbols in the bottom toolbar, and I also don't know how to search for symbols online If you can give me a tip, how to find a symbol that I need, this will be very useful.

Answer 1

Here are three suggestions. The first is my own, and the second and third are adapted from (http://www.logic.at/staff/salzer/etc/mhyphen/). Note that the first and second both output "math italic" text, but the third outputs "upright" text.

\documentclass{article}
\begin{document}
\newcommand\rnumber{\mathop{\mbox{$r$-$\mathit{number}$}}}
\[
\rnumber(5) = 120
\]
\end{document} 

\documentclass{article}
\usepackage{amsmath}
\mathchardef\mhyphen="2D % Define a "math hyphen"
\begin{document}
\newcommand\rnumber{\mathop{r\mhyphen number}}
\[
\rnumber(5) = 120
\]
\end{document} 

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\newcommand\rnumber{\operatorname{r-number}}
\[
\rnumber(5) = 120
\]
\end{document} 

LyX users should put the definitions (\usepackage, \newcommand, \mathchardef, etc.) in Document -> Settings -> LaTeX Preamble, and the usage (e.g. \rnumber(5) = 120) inside math-mode (Ctrl+M).