# Text across several summation symbols

I have a question on how to have the following in an equation.

\documentclass[12pt]{article}

\begin{document}

$$P(X)=\sum_{X\in A}\cdots \sum$$

\end{document}


Use \underset from amsmath.

\documentclass[12pt]{article}
\usepackage{amsmath}

\begin{document}

$$P(X)=\underset{X\in A}{\sum \cdots \sum}$$

\end{document}


If this is a common occurrence in your document, you might consider creating it as a new operator with limits, which is discussed in How to create my own math operator with limits? and in percusse's answer to your question here.

Here is one way via declaring an operator

\documentclass[12pt]{article}
\DeclareMathOperator*{\manysum}{\sum\cdots\sum}

\begin{document}

$$P(X)=\manysum_{X\in A}(x_{ijklm})$$
Also inline $$P(X)=\manysum_{X\in A}(x_{ijklm})$$.
\end{document}


\documentclass[12pt]{article}
\usepackage{amsmath}

\makeatletter
\newcommand{\Multi@Sum}[1]{%
\ifcase#1\relax\or
\or
\sum\sum\or
\sum\sum\sum\else
\sum\dots\sum
\fi
}
\newcommand\ssum{\DOTSB\mathop{\Multi@Sum{2}}\slimits@}
\newcommand\sssum{\DOTSB\mathop{\Multi@Sum{3}}\slimits@}
\newcommand\sdotssum{\DOTSB\mathop{\Multi@Sum{-1}}\slimits@}
\makeatother

\begin{document}

$$\sum_{x\in A}\quad \ssum_{x\in A}\quad \sssum_{x\in A}\quad \sdotssum_{x\in A}$$

\end{document}


This will respect the option nosumlimit or sumlimit (default) given to amsmath.

You may want to change the \sum\dots\sum line to

\sum\!\cdots\!\sum


getting, for \sdotssum_{x\in A} the output