# How to resize \Sum and \Prod commands

I'd like to make \sum and \prod symbols slightly smaller than they usually are. There are several related questions, but none of them does exactly what I need. I do not want them to be as small as \scriptsize or smaller; also, I want limits in textstyle and displaystyle to be as they originally are (that is, up and down in math mode; and next to $\sum$ and $\prod$ when inline). I have tried many things, but could not get what I desire. A (rather useless, I admit) MWE would be:

\documentclass{article}
\let\oldsum\sum
\renewcommand{\sum}{\oldsum}

\let\oldprod\prod
\renewcommand{\prod}{\oldprod}

\begin{document}
$$\sum \prod$$
\end{document}


How could I resize sum and prod keeping the limits as they usually are? Thank you all in advance for your time.

• it would be better to choose a different fomt that has a sum more to your liking. asking to change the size of sum is like asking to change the size of a it's possible but will look odd unless you change other characters in the font to match. do you want to make both the inline and the display sum smaller (these are different characters in most font setups)? Mar 30, 2017 at 10:07
• Please tell us more about the use case for wishing to make the summation and product symbols smaller. Also, how much smaller should the symbols be?
– Mico
Mar 30, 2017 at 10:09
• @DavidCarlisle, @Mico : Sorry, I admit the question may not be properly and fully specified. My bad. I only want to change the display sum smaller; I am happy with the size of inline. Also, let's say that I want \prod and \sum in display mode to be of the size of inline \prod and \sum; but keeping in the limits as they usually are in display mode. Shall I edit the question to make these points clear? Mar 30, 2017 at 10:12

Here's a solution compatible with amsmath:

\documentclass{article}
\usepackage{amsmath}
\usepackage{etoolbox}

\makeatletter
\newcommand{\changeoperator}[1]{%
\csletcs{#1@saved}{#1@}%
\csdef{#1@}{\changed@operator{#1}}%
}
\newcommand{\changed@operator}[1]{%
\mathop{%
\mathchoice{\textstyle\csuse{#1@saved}}
{\csuse{#1@saved}}
{\csuse{#1@saved}}
{\csuse{#1@saved}}%
}%
}
\makeatother

\changeoperator{sum}
\changeoperator{prod}

\begin{document}

Display style: $\displaystyle \sum_{k=1}^n a_k+\prod_{k=1}^n b_k$

\bigskip

Text style: $\sum_{k=1}^n a_k+\prod_{k=1}^n b_k$

\bigskip

Script style: $\scriptstyle \sum_{k=1}^n a_k+\prod_{k=1}^n b_k$

\bigskip

Scriptscript style: $\scriptscriptstyle \sum_{k=1}^n a_k+\prod_{k=1}^n b_k$

\end{document}


• I know I should not comment just to say thank you; but thank you. The solution is neat and works as expected. Mar 30, 2017 at 11:35
• @Héctor You can treat similarly also \bigoplus and so on. Mar 30, 2017 at 11:37
• I'll take that into account. So far, I am not using \bigcup, \bigcap and so on in my document; but if I do, I'll keep this in mind! By the way, can I treat capital Greek letters in the same way to get them larger? Should I start another question for this? Mar 30, 2017 at 13:25