[texhax] Infinity symbol output too small

[Heiko Oberdiek]

On Sun, Dec 30, 2012 at 01:53:14PM +0000, Dr A K Hannaby wrote:

> In amsmath book, why does the \infty (infinity) symbol display so small in
> math mode in comparison to other maths characters , say, x, y or a greek
> letter such as \beta (Beta)?
> 
> Is there a way of scaling the \infty only?

It could be scaled using \scalebox of package graphics(/graphicx). The
following example implements a scaled version \Infty that is scaled with
factor \InftyScale. The redefinition takes into account:
* Math styles (via \mathpalette), resizing of the symbol according to
  the current math style (subscript, ...)
* The horizontal mathematical axis is kept (by resizing the symbol on
  the baseline).
* The short form `^\Infty' can be used (by adding curly braces).

Since the line width is also scaled, the boldness increases by the
same factor using this scaling method.

\documentclass[12pt]{article}
\usepackage{graphicx}

\makeatletter
\newcommand*{\Infty}{%
  {\mathpalette\Infty at aux{}}%
}
\newcommand*{\Infty at scale}{1.2}% adjust to your needs
\newdimen\Infty at dim
\newcommand*{\Infty at aux}[2]{%
  \settoheight{\Infty at dim}{$#1\vcenter{}$}%
  \raisebox{\Infty at dim}{%
    \scalebox{\Infty at scale}{%
      \raisebox{-\Infty at dim}{$\m at th#1\infty$}%
    }%
  }%
}
\makeatother

\begin{document}
% Testing
\[ a + \infty = \frac{a_\infty}{+\infty^{-\infty}} \]
\tracingmacros=1
\[ a + \Infty = \frac{a_\Infty}{+\Infty^{-\Infty}} \]
\[ - \infty \Infty - \]
\end{document}

Yours sincerely
  Heiko Oberdiek