44

How can i write my own math operator with limits? I want it to look like: \sum\limits_{e=1}^{m} but with a capital A (if possible bigger than the normal text) instead of the sum. Thanks for the help!

|improve this question

migrated from stackoverflow.com Jul 18 '11 at 20:57

This question came from our site for professional and enthusiast programmers.

34

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}

enter image description here

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.

enter image description here

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}

enter image description here

|improve this answer
  • I'd like to do the same but using \star. What are the 4 sizes used in the choice? I'd like to use \LARGE\star. Is there different sizes for display or inline math? – Sigur May 11 '15 at 13:48
  • @Sigur I added the code for the big star; I used just 90 percent of the size of a summation symbol, because the star has large overshoot. – egreg May 11 '15 at 15:21
  • thanks so much. Amazing and beautiful. Since I like to use \textstyle size in displayed mode (the \sum in displaystyle is too big in my opinion) should I use \vphantom{\textstyle\sum}? – Sigur May 11 '15 at 15:32
  • @Sigur Just use \mathop{\textstyle\bigstar} – egreg May 11 '15 at 15:37
  • sorry. Use it where? In the text body? If I well understood, you made a box with the same height as the one produced by \sum. But every time I use \sum in display mode I use \textstyle and \limits o make the summation smaller. I'd like to define the star symbol in such a way that I don't need to use \textstyle inside display mode. Simply \[ \bigstar_{i=1}^n\] with the same size as \[ \textstyle \bigstar\limits_{i=1}^n\]. – Sigur May 11 '15 at 15:43
32

Use the \DeclareMathOperator* command provided by the amsmath package. Example:

\documentclass{article}
\usepackage{amsmath}
\DeclareMathOperator*{\Aop}{A}
\begin{document}
\[ \Aop^a_b \]
\end{document}
|improve this answer
  • 1
    Where is the difference between \DeclareMathOperator* and \DeclareMathOperator? – Martin Thoma Jan 9 '16 at 21:53
  • 7
    @moose \DeclareMathOperator* will use limits so subscript/superscript will go directly below and above the symbol, while \DeclareMathOperator will not use limits and so subscript/superscript will go below right and above right. – Bakuriu Jan 30 '16 at 9:25
9
\documentclass{article}
\usepackage{amsmath}
\def\Aop{\operatornamewithlimits{%
  \mathchoice{\vcenter{\hbox{\huge A}}}
             {\vcenter{\hbox{\Large A}}}
             {\mathrm{A}}
             {\mathrm{A}}}}
\begin{document}

\[ \Aop^a_b \sum_a^b \]

$ \Aop^a_b \sum_a^b $

\end{document}

enter image description here

|improve this answer
8

Use \mathop to turn A into a "math operator", and then use \limits to do sum-style limits:

 $$\mathop{A}\limits_{e=1}^{m}$$

Do you really want A, or do you want \bigwedge?

|improve this answer
5

egreg's answer is fine but works poorly for existing mathematical symbols. I recommend the following:

\newcommand{\operator}[1]{\mathop{\vphantom{\sum}\mathchoice
{\vcenter{\hbox{\huge $#1$}}}
{\vcenter{\hbox{\Large $#1$}}}{#1}{#1}}\displaylimits}

To define an operator 'A', you can now type

\newcommand{\opA}{\operator{\mathrm{A}}}

But you can also define an operator Theta:

\newcommand{\opTheta}{\operator{\Theta}}

Just remember that in the argument you pass to \operator, you are in math mode.

|improve this answer

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy