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sometimes when writing mathematical expression with partial derivatives, one needs to write a vertical bar afterwards and write the value at the which the partial derivatives are being computed as subscripts. See for example the bottom post here:

http://www.physicsforums.com/showthread.php?t=63809

However, the \mid symbol doesn't produce a tall bar that corresponds to the size of the partial derivatives term. Is there a way to have a taller bar?

PS: Some other posts here mention \middle| but this doesn't compile on my computer.

Thanks in advance....

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2 Answers

up vote 7 down vote accepted

Try

\left.\frac{\partial f}{\partial x}\right|_{x_0}

Or if you have \usepackage{amsmath}, you can use \rvert instead of the |. In fact, this is probably the better way to go.

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Thanks it works fine. I was using \rvert earlier also. My problem is that I used a custom partial derivative formulation from: tug.org/TUGboat/Articles/tb18-1/tb54becc.pdf .This was causing problems with the size of the vertical bar following the partial derivatives. –  yCalleecharan Sep 16 '10 at 9:27
    
1 vote up for the elegant solution. –  yCalleecharan Sep 16 '10 at 9:33
    
You can also use \biggr (or one of the other similar macros). As a side note, anyone (including the ISO) who thinks that e should be typeset upright should probably just be ignored (modulo hard publishers' requirements). =) –  TH. Sep 16 '10 at 9:38
    
\rvert and | are equivalent in this case because the class is ignored when a mathchar is used as a delimiter. –  Philipp Sep 16 '10 at 9:41
1  
Note that \left.\frac{\partial f}{\partial x}\right|_{x_0} causes there to be an extra \nulldelimiterspace of blank space to the left of the fraction. (By default, \nulldelimiterspace is 1.2pt.) Depending on what's around this expression, it's either a good idea or not worth the trouble to remove that extra space. –  MSC Mar 15 '13 at 19:37
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\middle should work in any current system. But it needs accompaigning \left+\right. Like braces in \left/right it will adapt its size to the size of the content:

\documentclass[a4paper,10pt]{article}

\begin{document}
$\left\{a\middle|a\right.$ 
$\left\{\int \middle|\int\right.$
$\int\mid \int$
\end{document}
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Yes it works fine. Thanks for explaining how to use it. –  yCalleecharan Sep 16 '10 at 9:29
    
\middle requires e-TeX, but as you say, any current system... –  TH. Sep 16 '10 at 9:31
    
Yes it's ok with my TeXLive. 1 vote up for the explanation. –  yCalleecharan Sep 16 '10 at 9:32
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