*Post by jfh**Post by b***@free.fr**Post by jfh*The NIST Handbook of Mathematical Functions equation 2.3.18 uses res with t=a underneath it to indicate the residue of a function of t at the point t=a,

but the following example puts it after res. What am I doing wrong?

\documentclass{article}

\usepackage{amsmath,amssymb}

\DeclareMathOperator{\res}{res}

\begin{document}

\begin{gather}

\res\limits_{t=a}\left[\frac{1}{t-a}\right]=1.

\end{gather}

\end{document}

Use in your preamble

\DeclareMathOperator*{\res]{res}

(with a star), the simply type

\res_{t=a}\left[\frac{1}{t-a}\right]=1.

(\limits is not necessary).

That worked perfectly! But I am still surprised that \limits fails for

user-defined operators. Maybe that's why AMS invented \DeclareMathOperator*

as well as \DeclareMathOperator

This is actually an intentional obstruction included by the authors

of \DeclareMathOperator: it defines \res to look ahead for \limits

and remove it if it finds one. It only does this once, so you

can write

\res\limits\limits

to get what you want.

The * version is more flexible in that you can follow your command

with either \limits or \nolimits or \displaylimits to select the

behavior you want.

In fact, you can globally change the behavior of commands defined

with \DeclareMathOperator*:

After \nonamelimits they behave as if followed by \nolimits and

after \namelimits they behave as if followed by \displaylimits.

You could also write

\makeatletter

\let\nmlimits@ \limits

\makeatother

to have them all behave as if followed by \limits.

Cheers,

Dan

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