Math symbol question: Vertical bar for ''evaluated at ...''

Question

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.

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.

Answer 1

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:

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

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.

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.

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 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.

Answer 2

I don't know how you would get this in LyX. However, if you're comfortable with writing things in mathmode by hand, I would write this as

T(s) = \frac{1}{H(\hat S)} \bigg\rvert_{\hat S = \epsilon^{1/n} \frac{s}{\omega_P}}

The relevant bit is the \bigg\rvert, which you can substitute with \Big\rvert or \Bigg\rvert to get a smaller or larger vertical stroke. If you would like to resize the vertical stroke automatically depending on what occurs to the left of it, I would recommend

T(s) = \left. \frac{1}{H(\hat S)} \right\rvert_{\hat S = \epsilon^{1/n} \frac{s}{\omega_P}}

where \left. puts an invisible left-bracket-like symbol on the left, whose right-side partner is the vertical stroke given by \right|. These pairs work equally for other braces/brackets.

Answer 3

Do not use | directly. Instead I suggest you use \rvert, which is provided by the amsmath package to address the overloading of the | symbol. See section 4.14.2 of the amsmath documentation.

Answer 4

Try the following:

\begin{equation}
  \left.\frac{\frac{1}{x}}{\frac{5}{1+\frac{x}{7}}}\right\vert_{-5}^{17}
\end{equation}

Answer 5

You could also try using \Bigg|_{f(x)=y} this would get you the vertical line at any scale you like!

Answer 6

When using Lyx, I found it very useful (and fast) to create a shortcut for the command math-delim . |. It creates a variable sized container with nothing on the left side and the \vert on the right side, so this works perfectly for me.

So: Tools > Preferences > Editing > Shortcuts... New... Function: math-delim . | (with the blank space bethween the dot and the vertical line) and choose your preferred keys for the shortcut.

Answer 7

How to stretch a vertical bar to be tall:

To stretch a vertical bar to be tall, such as to plug in values into a definite integral's antiderivative, add an invisible vertical bar on the left with \left., and a visible vertical bar on the right with \right|. Ex: \left.{\left[\cfrac{x}{\cfrac{a+b}{c}}\right]}\right|_{\;0}^{\;4} is

Note that the \; here is a wider space to space the numbers to the right of the vertical bar.

I just added this info. to this community wiki question here as well: Mathematics Stack Exchange: MathJax basic tutorial and quick reference