Add Multiple Arguments To Command With Comma

Question

Is there any way to define a command like:

\newcommand{\mysum}[2]{\sum\limits_{#1}^{#2}}

where the two arguments are separated by a comma instead of brackets?

So for example, I'd like to have:

\documentclass[12pt, letterpaper]{article}
\usepackage{amsmath}
%yet to be defined command%
\begin{document}
The sum given by $a=\mysum{n=1, \infty}$
\end{document}

Return the same thing as:

\documentclass[12pt, letterpaper]{article}
\usepackage{amsmath}
\begin{document}
The sum given by $a=\sum\limits_{n=1}^{\infty}$
\end{document}

E.g. https://tex.stackexchange.com/questions/378252/renewcommand-with-comma-separated-arguments — Joseph Wright, Mar 10 '24 at 22:09
Hello! excuse me, but what would be the advantage of using comma rather brakets? — Darío, Mar 10 '24 at 23:16
@Dario just faster. Less characters and no need to hit shift key. — EDS, Mar 11 '24 at 01:42

score 3 · Accepted Answer · answered Mar 12 '24 at 03:41

expl3's \clist_item:nn might be your friend:

\documentclass[12pt, letterpaper]{article}
\usepackage{amsmath}
\ExplSyntaxOn
\cs_new:Npn \mysum #1 {\sum\limits\sb{\clist_item:nn{#1}{1}}\sp{\clist_item:nn{#1}{2}}} 
\ExplSyntaxOff
\begin{document}
The sum given by $a=\mysum{n=1, \infty}$
The sum given by $a=\sum\limits_{n=1}^{\infty}$
\end{document}

score 2 · Answer 2 · answered Mar 12 '24 at 12:05

I'd not add \limits unconditionally and use a *-variant if you need it.

\documentclass{article}
\usepackage{amsmath}
\NewDocumentCommand{\mysum}{s >{\SplitArgument{1}{,}}m}{%
  \sum
  \IfBooleanT{#1}{\limits}%
  \mysumaux#2%
}
\NewDocumentCommand{\mysumaux}{mm}{_{#1}\IfValueT{#2}{^{#2}}}
\begin{document}
$\mysum{n=1,\infty}$ is good.
$\mysum*{n=1,\infty}$ is bad.
[
\mysum{n=1,\infty}\qquad \mysum{n\ge0}
]
\end{document}

You see that a single item in the argument is correctly treated as a subscript.

Add Multiple Arguments To Command With Comma

2 Answers2