# typing a straightline next to a dfrac? [duplicate]

I would like to type

how do I do it?

Thanks!

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## marked as duplicate by Gonzalo Medina, dustin, Werner, Sean Allred, cmhughesSep 2 '13 at 4:07

Provided you've loaded the amsmath and amsfonts packages, you can write something like

$\left. \frac{\mathrm{d}\mathbb{P}^{\beta}} {\mathrm{d}\mathbb{P}} \right|_{\mathcal{F}_t}$


\left and \right allows you to using grouping-like symbols and resize them to match the height of the material bracketed. In this case, you only have | which is not paired with anything else. So we use \left. to fill in for the missing grouping symbol.

Regarding $...$, this is for displayed math expressions. It is currently preferred over $$...$$ as it handles various spacing issues better, among other things.

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I trust you that this works and i will use it but can i ask how exactly does this make the | long? – Lost1 Sep 2 '13 at 0:42
you want the t outside the mathcal – Lost1 Sep 2 '13 at 0:44
also what is [ ]? never used this before – Lost1 Sep 2 '13 at 0:44
thanks a lot, really appreciate it. – Lost1 Sep 2 '13 at 0:49