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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 2

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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, 2010 at 9:27
  • 1 vote up for the elegant solution.
    – yCalleecharan
    Sep 16, 2010 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, 2010 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, 2010 at 9:41
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    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, 2013 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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