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I would like to use a small image in an equation, where a symbol like \alpha might otherwise be. Is there a nice way to do this?

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I have never tried \includegraphics in math mode, but I would expect it to work. Are you saying it doesn't? Or is it that you have some difficulty with vertical alignment (which I imagine could become problematic)? –  Harald Hanche-Olsen Feb 14 '11 at 16:33
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3 Answers

up vote 14 down vote accepted

It won't scale nicely with font size, but a simple approach is straightforward. The image should have a tight bounding box, which you can achieve with tools like pdfcrop.

\newcommand{\mysymbol}{\mathord{\includegraphics[height=1.6ex]{symbol}}}

\mathord is suitable for ordinary symbols, since you indicated that it would be used similarly as \alpha.

With the suggestions from the comments, I wrote a better solution.

\newcommand{\myfancysymbol}{
 {\mathchoice
  {\includegraphics[height=1.6ex]{symbol}}
  {\includegraphics[height=1.6ex]{symbol}}
  {\includegraphics[height=1.2ex]{symbol}}
  {\includegraphics[height=0.9ex]{symbol}}
 }
}

The symbol scales like a capital X for subscript and subsubscripts.

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Use height=1em, then the picture can be auto scaled. –  Leo Liu Feb 14 '11 at 16:42
    
@Leo Liu: It should, but it didn't work in my tests: $ \mysymbol_{\mysymbol_{\mysymbol}} $ gives 3x the same size with 1em or similar. –  Martin Scharrer Feb 14 '11 at 16:57
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@Martin: Use \mathchoice then. I used this trick in my own document years ago. –  Leo Liu Feb 14 '11 at 17:01
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I would suggest 1.6ex instead, which is about the height of an uppercase X. The 1em is actually the width of an uppercase M. –  Martin Scharrer Feb 14 '11 at 17:01
1  
I have incorporated all your comments to an improved solution. –  Mikael Öhman Feb 14 '11 at 17:15
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Yes, you can. There is nearly no difference between a image and a symbol. Just define a command for convenience. You can also use PSTricks or TikZ to draw such a symbol.

However, you may need to redefine the depth of the box, and refine the spacing using \mathbin etc.

A full example (suppose a logo.pdf exists):

\documentclass{article}
\usepackage{graphicx}
\def\xlogo#1{\includegraphics[width=#1em]{logo}}
\def\logo{{% mathord
  \mathchoice
    {\xlogo1}%
    {\xlogo1}%
    {\xlogo\defaultscriptratio}%
    {\xlogo\defaultscriptscriptratio}}}
\begin{document}
$\logo_{\logo_{\logo_\logo}}$
\end{document}
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It seems I'm too obstinate to use ex. :) –  Leo Liu Feb 14 '11 at 17:30
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Mikael and Leo both gave good answers so I won't repeat that information.

If you need the image centered with respect to binary operators, fractions, and the like, then you can use \vcenter{...} to perform that vertical centering.

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