62

How can I make a big summation sign? 

‎\begin{align}‎
‎\cos x‎ ‎=‎ ‎‎\sum\limits‎_‎{n=0}^{‎\‎‎infty‎} ‎\frac{(ix)^{2n‎}}{(2n)!}‎‎
\end{align}‎

this is the code which I'm using for summation

CarLaTeX
  • 62,716
Prelude
  • 4,242
  • 5
    Isn't that big enough? By the way, you don't need \limits in an align; and you don't need it elsewhere, either. – egreg Jul 11 '11 at 14:06
  • And you don't need \dfrac in an align, \frac is OK. – Leo Liu Jul 11 '11 at 14:13
  • I agree with @egreg: using a consistent size of \sum could be better than varying the size manually depending on the following expression. Additional fine-tuning can be ok, however I would compare such equation design in good books before. – Stefan Kottwitz Jul 11 '11 at 15:08
  • thank you very much , that's right but I'm typing my article just in the way my professor asked me ! – Prelude Jul 11 '11 at 15:16

3 Answers3

69

You can use the command \mathlarger of the relsize package. It increases the size and it can be nested. For example:

\documentclass{article}
\usepackage{amsmath}
\usepackage{relsize}
\begin{document}
\begin{equation}‎
‎‎\cos x‎ ‎=‎ \mathlarger{\mathlarger{‎‎\sum}}_{n=0}^{\infty}\frac{(ix)^2n}{(2n)!}‎‎
\end{equation}‎
\end{document}

equation with bigger sum symbol

.....

Smokeman
  • 3
Stefan Kottwitz
  • 231,401
  • 4
    this command cannot be used inside align environment. Is it true ? for me nothing happened when I used this. – creative Mar 25 '16 at 08:14
  • 1
    Works fine inside the align. – aiag Feb 11 '17 at 23:49
  • @aiag I experience the same problem as Hirak. Using pdfTeX 3.14159265-2.6-1.40.17 (TeX Live 2016/TeX Live for SUSE Linux). – el_tenedor Dec 11 '18 at 07:57
  • 1
    Just to add to the accepted answer, you should load the exscale package in order for relsize to scale maths symbols beyond the standard sizes. – Stefan Jul 24 '21 at 07:01
36

Well, there's always a graphicx solution.

\nsum[<optional>]

The command \nsum resizes the \sum symbol by the factor 1.4 (fits OP's fraction). It does take an optional argument to give another factor.

I admit that the \raisebox factor calculation is a bit sketchy as it uses the text style \sum symbol for the calculation but for cmr it's a good fit and I'm too lazy to take a closer look at the needed dimension calculation.

\resum{<arg>}

Another more dynamic approach would be to take the dimensions of the \sum's terms and resize the \sum sign so that it fits their vertical dimensions. To only specify the therms once the \resum also defines (overwrites) \s so that one can use

\resum{<what to sum>}_{foo}^{bar} \s

(I also tried to use \resizebox that takes the dimension instead of a factor, but I couldn't quite work out how to use \resizebox and \resizebox*.)

The second screenshot (produced by the lua-visual-debug package shows why \resum is in my eyes unstable and shouldn't be used. (But I don't think that a bigger \sum sign is even needed, anyway)

Code

\documentclass{article}
\usepackage{amsmath}
%\usepackage{lua-visual-debug} requires LuaTeX (used only for demonstration purposes)
\usepackage{graphicx}
\usepackage{calc}
\newlength{\depthofsumsign}
\setlength{\depthofsumsign}{\depthof{$\sum$}}
\newlength{\totalheightofsumsign}
\newlength{\heightanddepthofargument}

\newcommand{\nsum}[1][1.4]{% only for \displaystyle
    \mathop{%
        \raisebox
            {-#1\depthofsumsign+1\depthofsumsign}
            {\scalebox
                {#1}
                {$\displaystyle\sum$}%
            }
    }
}
\newcommand{\resum}[1]{%
    \def\s{#1}
    \mathop{
        \mathpalette\resumaux{#1}
    }
}

\newcommand{\resumaux}[2]{% internally
    \sbox0{$#1#2$}
    \sbox1{$#1\sum$}
    \setlength{\heightanddepthofargument}{\wd0+\dp0}
    \setlength{\totalheightofsumsign}{\wd1+\dp1}
    \def\quot{\DivideLengths{\heightanddepthofargument}{\totalheightofsumsign}}
    \nsum[\quot]%
}

% http://tex.stackexchange.com/a/6424/16595
\makeatletter
\newcommand*{\DivideLengths}[2]{%
  \strip@pt\dimexpr\number\numexpr\number\dimexpr#1\relax*65536/\number\dimexpr#2\relax\relax sp\relax
}
\makeatother

\begin{document}
\begin{equation}
  \cos x = \nsum_{n=0}^\infty \frac{(ix)^2n}{(2n)!}
\end{equation}
\begin{equation}
  \rlap{\rule[.57ex]{.55\linewidth}{.1pt}}\rlap{\rule{.55\linewidth}{.1pt}}
  \sum_{n=1}^\infty \nsum_{1.4} \nsum[2]_2 \nsum[2.5]_{2.5} \nsum[3]_{n=1}^\infty \nsum[3]_{\displaystyle n=1}^{\displaystyle \infty}
\end{equation}
\begin{equation}
     \cos x = \resum{\frac{(ix)^2n}{(2n)!}}_{n=0}^\infty \s \quad \resum{\frac{1}{2}}_{n=0}^\infty\s \quad \resum{\frac{\strut 1}{\strut 2}}_{n=0}^\infty\s 
\end{equation}‎
\end{document}

Output

Main output

A closer look at how \resum does (not) work

a closer look

Qrrbrbirlbel
  • 119,821
13

If you're willing to use the Mathtime Professional II font package, you could use its \xl\sum, \XL\sum, \XXL\sum etc commands to get larger summation symbols.

enter image description here

\documentclass{article}
\usepackage{newtxtext}
\usepackage[lite]{mtpro2}
\begin{document}
The summation symbols below are generated by \texttt{\string\sum} as well as by \texttt{\string\xl\string\sum}, \texttt{\string\XL\string\sum}, and  \texttt{\string\XXL\string\sum} of the \texttt{mtpro2} package. (There is also \texttt{\string\XXXL\string\sum}, but it's not shown here.)
\[
     \sum_{i=1}^N \frac{1}{2^{-i}} \qquad 
  \xl\sum_{i=1}^N \frac{1}{2^{-i}} \qquad 
  \XL\sum_{i=1}^N \frac{1}{2^{-i}} \qquad 
 \XXL\sum_{i=1}^N \frac{1}{2^{-i}}
\]
\end{document}

Two additional comments. (i) The mtpro2 font package isn't free of charge, although it's not exactly expensive either; actually, all that's needed to produce the large summation symbols is the lite subset of the package, which is free of charge. (ii) The mtpro2 math font package uses a "Times Roman" font style; this may or may not be to your liking.

Mico
  • 506,678