Declare math operator

Question

I'm trying to create a command with which to write

\declaremathoperator{ABC}

to get

\def\ABC{\operatorname{ABC}}

I tried to implement it like

\def\declaremathoperator#1
{ \def\csname #1\endcsname{\operatorname{#1}} }

but it doesn't work: Use of \csname doesn't match its definition.

It seems to me that the solution, if it exists, should be based on writing \#1, but at the same time so that TeX first makes a substitution of #1, and only then would begin to consider \ as the beginning of the command name.

score 4 · Accepted Answer · answered Feb 12 '22 at 10:37

4

Your gain with respect to

\DeclareMathOperator{\ABC}{ABC}

is very little. And the proposed definition is very dangerous. If it worked, you'd be able to say

\declaremathoperator{span}

and destroy your documents. You can do

\newcommand{\newmathoperator}[1]{%
  \expandafter\DeclareMathOperator\csname #1\endcsname{#1}%
}
\newmathoperator{ABC}
\newmathoperator{span}% <--- would give error

which would warn you in case the proposed command already has a definition. The \expandafter is necessary so \DeclareMathOperator sees the control sequence you want to define, rather than \csname.

answered Feb 12 '22 at 10:37

egreg

1,121,712

Is there even a way to define a command inside another command, provided that the name of the new command is given by a string? – Alexey Ismagilov Feb 12 '22 at 11:51
@AlexeyIsmagilov The same idea applies. – egreg Feb 12 '22 at 12:55

Declare math operator

1 Answers1