Redefining Commands Using DeclareRobustCommand

Question

I am trying to create the following commands. I want to replace \exp by a command that takes an input and outputs \exp(#1). Trying to copy something that I was shown before, I tried the following

\let\EXP\relax
\DeclareRobustCommand{\EXP}{\exp}
\rewnewcommand{\exp}[1]{\EXP(#1)}

However, upon compiling, I get a TeX capacity exceeded, sorry error. If I don't redefine exp, but call it something like expm, then there are no issues. I'd prefer to redefine it though. How can I get around this?

Answer 1

You shouldn't do this: I see no advantage in typing \exp{3} over \exp(3), unless you want to do something more, that is, adding the possibility of sizing the parentheses.

This can be done with mathtools.

\documentclass{article}
\usepackage{mathtools}

\DeclarePairedDelimiter{\paren}{(}{)}
\let\originalexp\exp

\renewcommand\exp{\originalexp\paren}

\begin{document}

\begin{equation*}
\exp{x}\quad\exp[\big]{x}\quad\exp*{\frac{\pi}{2}}
\end{equation*}

\end{document}

However, I'd avoid this and rather define \expp:

\documentclass{article}
\usepackage{mathtools}

\DeclarePairedDelimiter{\paren}{(}{)}
\newcommand\expp{\exp\paren}

\begin{document}

\begin{equation*}
\expp{x}\quad\expp[\big]{x}\quad\expp*{\frac{\pi}{2}}
\end{equation*}

\end{document}

What's going wrong with your definition?

Upon calling \exp{1}, TeX will do \EXP(1), which becomes \exp(()1) which becomes \EXP(()1), which becomes \exp(()()(1)…