How do I define a math mode formula with a caret ^ in LaTex?

Question

This question has two parts. First, is there a way to define a macro only for math mode?

Second, how do I specifically get the following definition to work correctly?

\def\fi{f^{-1}}

One additional point is that I'm trying to create this definition within a local scope rather than global scope, but I'm not sure that's relevant.

Answer 1

  \def\fi{f^{-1}}

Don't even think of redefining \fi \fi is the TeX primitive (if backwards) that terminates every conditional construct. If you redefine this then more or less every construct in LaTeX will break.

  \def\finv{f^{-1}}

would define \finv to produce f^-1 which is what I assume you want rather than a literal ^ in the printed output?

Answer 2

1. You can use \ifmmode, e.g. \def\fim{\ifmmode f^{-1}\fi}

2. Do not redefine \fi unless you are a wizard. It is used in all \if.. constructions. Define \fim instead.

Answer 3

For starters \fi is a TeX primitive and it declares the end of an if statement. To answer your question you can use the amsmath package with:

\def\finv{\ensuremath{f^{-1}}}

This ensures you are in math mode every time. Yet a variant of this using the fixltx2e and xspace packages you can create the same command by using \TextOrMath{<text mode>}{<math mode>}:

\newcommand{\finv}{\TextOrMath{$f^{-1}$\xspace}{f^{-1}}}