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while reading a book on maths lately, I have seen a small integral delimiter such that, in what follows:

\begin{equation}
\sum_i^j A_{ij}\int\limits_{-\infty}^{+\infty} \cos x dx 
\end{equation}

the sum and integral would be of the same height. Are you aware of something like that? Thank you

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Are you fine with using smaller symbols for both the sum and the integral? Or you really want an integral as big as the usual sum? –  Juan A. Navarro Oct 7 '10 at 14:38
    
yes, I want an integral sign as big as the usual sum –  pluton Oct 7 '10 at 15:09
    
The size of the summation sign might differ depending on your math font. Do you mean the computer modern \sum? –  Caramdir Oct 8 '10 at 20:17
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4 Answers 4

up vote 2 down vote accepted

With an up-to-date texlive-2010, if you use Asana Math font with unicode-math package (requires XeTeX or LuaTeX), you will get an integral that as high as the summation symbol:

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{Asana-Math.otf}

\begin{document}

\begin{equation}
\sum_i^j A_{ij}\int\limits_{-\infty}^{+\infty} \cos x dx 
\end{equation}

\end{document}
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ok thanks, I'll try to give it a try soon. –  pluton Oct 10 '10 at 14:00
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\int is a "variable-sized symbol", so that it comes in two sizes: one for in-line formulas and one for display-formulas. The same is true for \sum; it just so happens that the text-style integral is almost the same height as the display-style sum symbol (in Lamport's LaTeX User's Guide and Reference Manual, both are about 4 mm tall, the display-style sum style a bit more, while the text-style sum symbol is only about 3 mm tall; the display-style integral, by contrast, is a bit more than 7 mm tall). So all you want is the integral sign to be displayed in text-mode, but only the integral sign (so the sum symbol is not changed in size).

One way to accomplish this is to define a macro \smallint as \def\smallint{\begingroup\textstyle \int\endgroup}. Upon testing it, it shows just a shade smaller than a displaystyle summation (if you put limits on the integral but not on the summation, they look about the same); if you have limits on the sum and the integral, then both done in \textstyle looks better, but then you need to use the \limits command after \sum so that the limits occur above and below the sigma, instead of right after. Thus, if you have limits on the summation, I would suggest

\begin{equation}
\sum_{i}^j A_{ij}\begingroup\int\endgroup_{-\infty}^{+\infty}\cos x\,dx
\end{equation}

or

\begin{equation}
\mathop{\textstyle\sum}\limits_i^j 
   A_{ij}\begingroup\textstyle\int\endgroup_{-\infty}^{+\infty}\cos x\,dx
\end{equation}

(or using a macro for the small integral sign). (Note by the way the thin space before the dx in the integral).

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1  
This isn't quite right. You need to use \begingroup\textstyle\int\endgroup and not {\textstyle\int}. It is less obvious with \sum. –  TH. Oct 8 '10 at 20:57
    
I'm not sure what the difference is; I thought \begingroup and \endgroup just amount to the same thing as localizing things by the use of curly brackets. –  Arturo Magidin Oct 8 '10 at 21:00
    
PS How do you get the multiline display to show in the page? –  Arturo Magidin Oct 8 '10 at 21:01
1  
In many cases they are the same, but not always. In math mode, braces introduce a new subformula whereas \begingroup ... \endgroup is just a new group. If you compare the outputs of the two, the difference should be clear. The lower limit for the integral is too far to the right if you use {...}. Of course, you may want them to line up vertically even though there is extra space. In that case, braces work nicely. –  TH. Oct 8 '10 at 21:03
    
Ah; thanks. I also see now how to get the multiline display. –  Arturo Magidin Oct 8 '10 at 21:03
show 2 more comments
\begin{equation}
\textstyle \sum_i^j A_{ij}\int\limits_{-\infty}^{+\infty} \cos x dx 
\end{equation}
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thanks, that could be something like this. But I was also thinking on a specific font offering this small integral delimiter. –  pluton Oct 7 '10 at 12:33
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I'm not in front of a tex installation at the moment, but I think you're looking for

\smallint 
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Thanks but I think it is too small. –  pluton Oct 7 '10 at 15:10
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