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When I want to show evaluation of limits of an integral, I would type
\int_1^2 x\; dx=\frac{x^2}{2}|_1^2=4-\frac{1}{2}=\frac{7}{2}
How do I get the vertical bar showing the limits big enough? I have found \bigg and \Big but I would like it to autosize like \left. It seems harder because there isn't a left side to figure out what is inside. I tried \left<SPACE> and \right \mid, but didn't find success.
Use \left. and \right|
The left/right just has to be matched, but the symbols need not be the same.
\[ \int^{2}_{1} x\;dx = \left. \frac{x^{2}}{2}\right|^{2}_{1} = 4 - \frac{1}{2} = \frac{7}{2} \]
\left must be followed by either a delimiter, or a period that indicates that no delimiter is being used; same with \right.
Jun 15, 2011 at 4:17
I usually either use manual sizing with some space attached (this can be done with, in increasing order of size, \big, \Big, \bigg, and \Bigg. See below, in the order given, next to the fraction:
\[ \frac{x^2}{2}\big|;\qquad \frac{x^2}{2}\Big|;\qquad \frac{x^2}{2}\bigg|;\qquad \frac{x^2}{2}\Bigg|; \]
To get better spacing, you can use \bigr or \bigm (or suitably sized). \bigl is used for left delimiters such as (, \bigr for right delimiters such as ), \bigm for notation occurring "in the middle" such as \vert (which one it is determines the spacing on left and right); this uses \bigr, etc:
\[ \frac{x^2}{2}\bigr|;\qquad \frac{x^2}{2}\Bigr|;\qquad \frac{x^2}{2}\biggr|;\qquad \frac{x^2}{2}\Biggr|; \]
and this uses \bigm, etc:
\[ \frac{x^2}{2}\bigm|;\qquad \frac{x^2}{2}\Bigm|;\qquad \frac{x^2}{2}\biggm|;\qquad \frac{x^2}{2}\Biggm|; \]
(note the difference in spacing).
Alternatively, you can use the auto-sizing of \left and \right. Each one should be followed by a delimiter of some kind, or by a period; a period means that no delimiter is placed; every \left must come with a \right, and vice-versa, but the sizing is very precise; if you want an oversized bar, you either need to add some vertical phantom or strut to make \LaTeX think your expression is "taller" and/or "deeper". Below I use \left.\frac{x^2}{2}\right|, preceded by \Bigr and followed by \Biggr for comparison:
\[ \frac{x^2}{2}\Bigr|;\qquad \left.\frac{x^2}{2}\right|; \qquad \frac{x^2}{2}\Biggr|; \]
For a bigger one, you can add a "tall" vertical phantom with successive exponents or some other construct; e.g.,
\[ \left.\frac{x^2\vphantom{2^{2^{2^2}}}}{2}\right|; \]
\vphantom creates a width-less box with the height of whatever you type; essentially, it creates the vertical space that would be needed to fit what you are typing but doesn't type it. \hphantom creates a height-less box with the width of whatever it is you type, leaving the blank horizontal space that would be needed to type it but without typing it.
Jun 15, 2011 at 4:42
\makebox, but this is a quick and dirty way of getting the job done.
Jun 15, 2011 at 17:10
I think \bigg\vert works:
\[ \int_1^2 x\ dx=\frac{x^2}{2}\bigg\vert_1^2=4-\frac{1}{2}=\frac{7}{2}.\]
\left. <stuff> \right|to autosize a delimiter to the size of <stuff>, e.g. $$\left.\frac{x^2}{2}\right|_1^2$$ However, this should probably go on the TeX.SE site.