Formatting capital letters in math mode

Question

This is perhaps a simple question, but I would like to print a capital I in my LaTeX document (beamer specifically) inside a $...$ construct. I would like my I to appear more substantial by having the horizontal lines at top and bottom, however this is not what I am getting.

Any suggestions?

Answer 1

Math fonts in beamer are set in serif by default. To change this, see How to get beamer math to look like article math (use the mathserif class option). On a case-by-case basis, you could use $...\mathrm{I}...$ to obtain a serif-style I:

\documentclass{beamer}% http://ctan.org/pkg/beamer
\begin{document}
\begin{frame}
  I \quad $I$ \quad $\mathrm{I}$ \quad $\textrm{I}$
\end{frame}
\end{document}

Of course, if you're using this "I" on a more frequent and contextual-specific basis, consider using a macro like

\newcommand{\upshapeI}[1]{\textrm{\upshape I}}

The above suggestions follows the principles in Consistent typography.