# making a big summation sign

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

-
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 ! – Negin Jul 11 '11 at 15:16

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}
$$‎ ‎‎\cos x‎ ‎=‎ \mathlarger{\mathlarger{‎‎\sum}}_{n=0}^{\infty‎}\frac{(ix)^2n}{(2n)!}‎‎$$‎
\end{document}


-
thank you Stefan that was very useful – Negin Jul 11 '11 at 15:18
this command cannot be used inside align environment. Is it true ? for me nothing happened when I used this. – Hirak Mar 25 at 8:14

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


## Output

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

-

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.

\documentclass{article}
\usepackage{times,mtpro2}
\begin{document}
The summation symbols below are generated by
\texttt{\textbackslash sum} and by
\texttt{\textbackslash xl\textbackslash sum},
\texttt{\textbackslash XL\textbackslash sum}, and
\texttt{\textbackslash XXL\textbackslash sum} of the
\textbackslash{mtpro2} package. There is also
\texttt{\textbackslash XXXL\textbackslash sum},
but it's not shown here.
$\sum_{i=1}^T \frac{1}{2^{-i}} \qquad \xl\sum_{i=1}^T \frac{1}{2^{-i}} \qquad \XL\sum_{i=1}^T \frac{1}{2^{-i}} \qquad \XXL\sum_{i=1}^T \frac{1}{2^{-i}}$
\end{document}


Do note, though, that (i) these fonts aren't free (though not exactly expensive either) and (ii) they are in the "Times Roman" font style, which may or may not be to your liking.

-