How can I specify a long list of math operators?

Question

The preambles of my LaTeX documents often include many many lines of \DeclareMathOperator instructions, e.g.

\DeclareMathOperator{\Rep}{Rep}
\DeclareMathOperator{\Tet}{Tet}
\DeclareMathOperator{\Maps}{Maps}
\DeclareMathOperator{\Diff}{Diff}

Is there a nice way to map some macro over a list, so I could do this more concisely, and with less copying and pasting when I add a new math operator?

Answer 1

Updated solution using the features of etoolbox which has essentially implemented the “\MapCommand” and named it \forcsvlist

\documentclass{article}
\usepackage{amsmath}
\usepackage{etoolbox}

\newcommand{\DeclareMyOperator}[1]{%
  \expandafter\DeclareMathOperator\csname #1\endcsname{#1}
}
\newcommand{\DeclareMathOperators}{\forcsvlist{\DeclareMyOperator}}

\DeclareMathOperators{Rep,Tet,Maps,Diff}

\begin{document}
Operators: $\Rep, \Tet, \Maps, \Diff$
\end{document}

“For historical reasons”, I leave my original answer bellow.

---

Combining the previous answers from Grigory and Andrew I was able to come up with the following somewhat cleaner implementation which also exposes a nice user interface.

\documentclass{article}
\usepackage{amsmath}

\makeatletter
\def\ops@declare#1{%
  \expandafter\DeclareMathOperator\csname #1\endcsname{#1}
}
\def\ops@scan#1,{%
  \ifx#1\relax
    \let\ops@next\relax
  \else
    \ops@declare{#1}\let\ops@next\ops@scan
  \fi\ops@next
}
\newcommand{\DeclareMathOperators}[1]{\ops@scan#1,\relax,}
\makeatother

\DeclareMathOperators{Rep,Tet,Maps,Diff}

\begin{document}
Operators: $\Rep, \Tet, \Maps, \Diff$
\end{document}

Answer 2

There are several ways to do it using different programming facilities of different packages. Here's what it looks like using the LaTeX2e kernel command \@for to map over a comma-separated list:

\makeatletter
\newcommand\MakeMathOperators[1]{%
  \@for\@ii:=#1\do{%
    \expandafter\DeclareMathOperator\@ii
  }%
}
\makeatother
\MakeMathOperators{
  \rep  {Rep}  ,
  \tet  {Tet}  ,
  \maps {Maps}
}

Answer 3

Combining the previous answers with the ones to the related question about scanning over a list of somethings I came up with the following solution, using etoolbox version 2.0 (2010-08-21) or later.

\newcommand{\define}[4]{\expandafter#1\csname#3#4\endcsname{#2{#4}}}
\forcsvlist{\define{\DeclareMathOperator}{}{}}{Rep, Tet, Maps, Diff}
\forcsvlist{\define{\newcommand}{\mathcal}{c}}{A,B,C,D,E,F,G,H,I,J,K}

The last line defines \cA as \mathcal{A} for all letters in the list.

If one wants a different list separator, e.g. ;, one can use \DeclareListParser*{\formylist}{;} and then replace \forcvslist with \formylist.

Answer 4

I'd probably do this differently if I were coding it today (as I've learnt a lot more about TeX in the last decade), but here's something like how I did it for my thesis:

\documentclass{article}

\usepackage{amsmath}

\makeatletter
\def\my@shift#1:#2.{#1}
\def\my@trunc#1:#2.{#2}
\def\my@void{}\relax

\newcommand{\Mops}[1]{%
 \def\my@test{}\relax
 \def\my@list{#1:}\relax
 \loop\ifx\my@test\my@void\relax
 \edef\my@elt{\expandafter\my@shift\my@list.}\relax
 \edef\my@list{\expandafter\my@trunc\my@list.}\relax
 \expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\DeclareMathOperator\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter{\expandafter\expandafter\expandafter\csname \expandafter\my@elt\expandafter\endcsname\expandafter}\expandafter{\my@elt}
 \ifx\my@list\my@void
 \def\my@test{t}
 \fi
 \repeat}

\makeatother

\Mops{Det:Diff:Rep}

\begin{document}
\(\Det \Diff \Rep\)
\end{document}

The test in the loop could probably be cleaned up, and that is a rather horrendous number of \expandafters! But it works.

Answer 5

Here's a solution from Kevin Walker's LaTeX preambles:

% tricky way to iterate macros over a list
\def\semicolon{;}
\def\applytolist#1{
    \expandafter\def\csname multi#1\endcsname##1{
        \def\multiack{##1}\ifx\multiack\semicolon
            \def\next{\relax}
        \else
            \csname #1\endcsname{##1}
            \def\next{\csname multi#1\endcsname}
        \fi
        \next}
    \csname multi#1\endcsname}

% \DeclareMathOperator{\pr}{pr} etc.
\def\declaremathop#1{\expandafter\DeclareMathOperator\csname #1\endcsname{#1}}

\applytolist{declaremathop}{pr}{im}{gl}{ev}{coinv}{tr}{rot}{Eq}{obj}{mor}{ob}{Rep}{Tet}{cat}{Maps}{Diff}{Homeo}{sign}{supp}{Nbd}{res}{rad};

Answer 6

Put the whole list of unabbreviated \DeclareMathOperator macros in a file myoperators.sty, somewhere in your latex path (I suggest ~/tex/). Then add \usepackage{myoperators} at the top of any .tex file that uses those operators.

Do this for any macro you use more than once.

Answer 7

Not quite what you're looking for, but I'd probably write the quick hack:

\newcommand{\OP}[1]{\DeclareMathOperator{#1}}
\OP{Rep}
\OP{Tet}

and so forth. Moreover if I were to use these a lot, I'd just write them once and include them anywhere.

Answer 8

E.g.

\def\deflist#1{\ifx#1\stop\let\next=\kill\else\let\next=\parse\fi\next{#1}}  
\def\kill#1{\relax}
\def\parse#1#2{\newcommand{#1}{\operatorname{#2}}\deflist}

\deflist
\holim{holim}
\hocolim{hocolim}
\stop

works (although I can't recommend using such tricks).