# use of limits after a non-math operator

I would like to write the following:

$\mu_{s,r} = \mbox{mean}_ {i \in N}(X_{i,s,r})$


but where the {i \in N} is underneath the word "mean". I tried \limit but it doesn't work unless it's a math operator. I understand this can ruin the look but I am making slides and want to see how it appears.

Thanks!

\documentclass{standalone}
\usepackage{amsmath}
\begin{document}
$\underset{i \in N}{\operatorname{mean}}$
\end{document}


As egreg pointed out in the comments the following works too

\documentclass{article}
\usepackage{amsmath}
\begin{document}
$\operatorname*{mean}\limits_{n \in N}$
$\operatorname*{mean}_{n \in N}$
\end{document}


In a display style math environment you don't need to write \limits.

• Throws an error. I think what you meant though was: $\underset{\operatorname{i \in N}}{\mbox{mean}}$ which works. – user1357015 May 22 '13 at 16:28
• @user1357015 It works now on my pc – Dominic Michaelis May 22 '13 at 16:32
• What about $\operatorname*{mean}\limits_{i\in N}$? The \limits wouldn't be necessary in display math mode. – egreg May 22 '13 at 16:32
• @egreg it works too (not surprising after you said it) i gonna add it to my answer – Dominic Michaelis May 22 '13 at 16:35
• Revision fixed it! Many thanks :-). – user1357015 May 22 '13 at 16:36

If you're using beamer you already load amsmath. However, in general, this works:

\documentclass{article}
\usepackage{amsmath}

\DeclareMathOperator*{\mean}{mean}

\begin{document}
\section{Long version}

In line: $\mu_{s,r} = \operatorname*{mean}\limits_{i\in N}(X_{i,s,r})$

Displayed:
$\mu_{s,r} = \operatorname*{mean}\limits_{i\in N}(X_{i,s,r})$

\section{Short version}

In line: $\mu_{s,r} = \mean\limits_{i\in N}(X_{i,s,r})$

Displayed:
$\mu_{s,r} = \mean\limits_{i\in N}(X_{i,s,r})$

\end{document}


Of course you'll use only one of the methods. For a "one shot" operator, \operatorname* is easier. For several usages of the operator, the \DeclareMathOperator* way is better.

The difference between \operatorname and \operatorname* (reflected in usage of \DeclareMathOperator and \DeclareMathOperator*) is that the latter defines an operator that in displays takes limits above and below, like \sum or \max, and in inline formulas respects the presence of \limits.