I want to define \ext to behave exactly like \lim.
I tried \newcommand{\ext}{{\mathrm{ext}}\,} but that doesn't behave exactly like \lim.
[Tex/LaTex] How to define a math operator behaving like \lim or \sum with limits
math-modemath-operators
Related Solutions
I would try with sideset from the amsmath package:
\begin{equation}
\sideset{}{_i}\bigoplus_{j=1}^{d}
\end{equation}
We can scale the symbol to the height plus depth of the summation and then vertically center it with respect to the formula axis.
\documentclass{article}
\usepackage{amsmath}
\usepackage{graphicx}
\makeatletter
\DeclareRobustCommand\bigop[1]{%
\mathop{\vphantom{\sum}\mathpalette\bigop@{#1}}\slimits@
}
\newcommand{\bigop@}[2]{%
\vcenter{%
\sbox\z@{$#1\sum$}%
\hbox{\resizebox{\ifx#1\displaystyle.9\fi\dimexpr\ht\z@+\dp\z@}{!}{$\m@th#2$}}%
}%
}
\makeatother
\newcommand{\bigstar}{\DOTSB\bigop{\star}}
\newcommand{\bigA}{\DOTSB\bigop{\mathrm{A}}}
\begin{document}
\[
\sum_{i=1}^n\bigA_{i=1}^n x_i\dots\bigstar_{i=1}^n x_i
\qquad
\textstyle
\sum\bigA\bigstar_{i=1}^n x_i
\qquad
\scriptstyle
\sum\bigA\bigstar_{i=1}^n x_i
\qquad
\scriptscriptstyle
\sum\bigA\bigstar_{i=1}^n x_i
\]
\end{document}
A simpler but not not scalable version (it won't work in
\newcommand{\opA}{\mathop{\vphantom{\sum}\mathchoice
{\vcenter{\hbox{\huge A}}}
{\vcenter{\hbox{\Large A}}}{\mathrm{A}}{\mathrm{A}}}\displaylimits}
In this way the "A" will be as large as the \sum symbol.
An enhanced version, where one can specify a correction factor for the big symbol in display style, as different symbols seem to require different factors.
\documentclass{article}
\usepackage{amsmath}
\usepackage{graphicx}
\makeatletter
\DeclareRobustCommand\bigop[2][1]{%
\mathop{\vphantom{\sum}\mathpalette\bigop@{{#1}{#2}}}\slimits@
}
\newcommand{\bigop@}[2]{\bigop@@#1#2}
\newcommand{\bigop@@}[3]{%
\vcenter{%
\sbox\z@{$#1\sum$}%
\hbox{\resizebox{\ifx#1\displaystyle#2\fi\dimexpr\ht\z@+\dp\z@}{!}{$\m@th#3$}}%
}%
}
\makeatother
\newcommand{\bigstar}{\DOTSB\bigop{\star}}
\newcommand{\bigA}{\DOTSB\bigop[0.92]{\mathrm{A}}}
\newcommand{\bigDelta}{\DOTSB\bigop[1.05]{\Delta}}
\begin{document}
\[
\sum_{i=1}^n\bigA_{i=1}^n\bigDelta_{i=1}^n x_i\dots\bigstar_{i=1}^n x_i
\]
\begin{center}
$\textstyle
\sum \bigA \bigstar \bigDelta_{i=1}^n x_i
\qquad
\scriptstyle
\sum \bigA \bigstar \bigDelta_{i=1}^n x_i
\qquad
\scriptscriptstyle
\sum \bigA \bigstar \bigDelta_{i=1}^n x_i
$
\end{center}
\end{document}
Best Answer
If you use
amsmath, which is recommendable for math texts in any way, a similar definition to\limissince
amsmath, specificallyamsopn.sty, defines: