[Tex/LaTex] Math symbol question: Vertical bar for ”evaluated at …”


How do I insert the line "|" after the equation in LaTeX (see image below)?
I'm using LyX so if you can point me to the symbol of that line is also OK.

enter image description here

I don't know if this line has a proper name so the title of this question may be very vague. If you could provide me a name, I'll edit this question's title.

Best Answer

You could just type the symbol (|) directly. This won't scale, to get it larger you could use the same technique as Niel de Beaudrap. In the LyX GUI this is done via the Insert Delimiter button on the math toolbar: button for "insert delimiter" in LyX

Set the left delimiter to None, and the right to |. Uncheck Keep matched, and let the Size be set to Variable:

delimiter options in LyX

In LyX this looks like as below (left). The dotted vertical line indicates an invisible delimiter (as \left. in Niels example). Result in PDF on the right.

LyX view of fraction with delimiters PDF output of the previous image

Edit in response to Marcs answer:

To use \rvert I think you have to use ERTs. If you don't have any other math constructs that use amsmath, you may have to make LyX use this package manually: Document --> Settings --> Math options. Uncheck Use AMS math package automatically, and check Use AMS math package.

enabling amsmath in LyX

In your equation, add an ERT (Ctrl + L) and type \biggr\rvert. That is, the first backslash may appear automatically, in which case don't type it.

\biggr\rvert in LyX

\biggr is one of several commands for manually scaling a delimiter, rather than the automatic provided by \left \right. Other sizes are \bigr, \Bigr and \Biggr, with the latter being the largest. For left delimiters, replace r with l. (See section 4.14.1 Delimiter sizes in amsmaths manual.)

Should you want to use \left\right, you need to add an ERT with \left. before the fraction (or whatever it is) and have \right\rvert in the one after.

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