[Tex/LaTex] How to place text as subscript under mathematical operator in equation

math-modemath-operators

I would like to put some text in math mode below a mathematical operator (or a symbol), similar to \substack in \sum, as the red text below the \max operator in the following image

How to do this?

Best Answer

You should place the expression in the subscript, as shown below. Most LaTeX books explain this. E.g.

\documentclass{article}

\begin{document}
\begin{itemize}
    \item \textbf{Display mode}:
        \[\max_{1 \leq i \leq N}\]
    \item \textbf{Inline mode}: version without \verb!\limits! would look like \(\max_{1 \leq i \leq N}\), version with \verb!\limits! would look like\(\max\limits_{1 \leq i \leq N}\) inside a text.
\end{itemize}
\end{document}

Note how \limits command force the subscript under operator in inline mode (if you think you need \limits, think again — maybe the defaults look better after all! cf. this answer here on TeX.se).

If you find that the subscripted expression is too long and introduces excessive whitespace, you could use \smashoperator macro from the mathtools package, as in this post.

Related Solutions

[Tex/LaTex] How to create the own math operator with limits

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.

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}

[Tex/LaTex] Large Blackboard bold R operator with text underneath

This does the job nicely I think (thanks karlkoeller for suggesting improvements):

enter image description here

\documentclass[a4paper]{article}

\pagestyle{empty}

\usepackage{amsmath,amsfonts,relsize,graphicx,dsfont}

\makeatletter
\newcommand*\smallR{\mathds{R}} % <-- this is your symbol
\newcommand*\yo@bigR[2]{\text{#2\raisebox{-#1ex}{$\smallR$}}}
\DeclareRobustCommand*\bigR{\mathop{\mathchoice
  {\yo@bigR{0.5}{\larger\larger\larger\larger}} % displaystyle
  {\yo@bigR{0.4}{\larger\larger}} % textstyle
  {\yo@bigR{0.3}{\larger\larger}} % scriptstyle
  {\text{\scalebox{1.4}{\raisebox{-0.3ex}{$\smallR$}}}} % scriptscriptstyle
  }\displaylimits}
\makeatother

\begin{document}
\begin{equation*}
\begin{bmatrix} x \\ y \\ z \end{bmatrix}_{\substack{\text{some text}\\\text{other text}}}
= 
\sum_x\bigR_{\text{sys1}\rightarrow\text{sys2}}
\begin{bmatrix} X \\ Y \\ Z \end{bmatrix}_{\substack{\text{more text}\\\text{also text}}}
\end{equation*}

\centering

\section{In section title $\sum_x\bigR_{\text{sys1}\rightarrow\text{sys2}}$}

Textstyle: \qquad $\sum_x\bigR_{\text{sys1}\rightarrow\text{sys2}}$

Scriptstyle: \qquad $\scriptstyle
\sum_x\bigR_{\text{sys1}\rightarrow\text{sys2}}$

Scriptscriptstyle: \quad $\scriptscriptstyle
\sum_x\bigR_{\text{sys1}\rightarrow\text{sys2}}$

\end{document}

It would somehow work by just using:

\newcommand\bigR{\mathop{\text{\LARGE\raisebox{-0.5ex}{$\mathds{R}$}}}\limits}

The rest of the mess above is to make it work in any environment and possibly in any font size.

Best Answer

Related Solutions

[Tex/LaTex] How to create the own math operator with limits

[Tex/LaTex] Large Blackboard bold R operator with text underneath

Related Question