# How to get a vertical bar which is longer than \mid ?

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:

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.

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.

• 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
• 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

\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}

• 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
• see also my question: tex.stackexchange.com/questions/222222/… – mystery Jan 8 '15 at 6:59