Everyone seems to ask about this and the usual solution seems to be to use \lvert and \rvert with the amsmath package, but that doesn't work for me either.
example:
f_{3,2} = \left(\sqrt{13}-2-\lvert \frac{\sqrt{13}}{6}+2-2\sqrt{7}\left(1+\delta V\right)\rvert\right)/4
Here's what I get
I want the absolute value bars to scale taller in accordance with the content.
What am I doing wrong?
You can scale then with \left\lvert and \right\rvert, just as with parentheses.
f_{3,2} = \left(\sqrt{13} - 2 - \left\lvert \frac{\sqrt{13}}{6} + 2
- 2\sqrt{7}\left(1 + \delta V\right) \right\rvert \right)/4
If you load the mathtools package, you can use a \DeclarePairedDelimiter command which simplifies scaling delimiters: writing \DeclarePairedDelimiter{\abs}{\lvert}{\rvert} defines two commands: \abs, which delimits its argument with \lvert and \rvert, and \abs*, which does the same, but scaling it automatically.
Here's what this would look like for your code.
% in preamble
\usepackage{mathtools}
\DeclarePairedDelimiter{\paren}{(}{)}
\DeclarePairedDelimiter{\abs}{\lvert}{\rvert}
% document
f_{3,2} = \paren*{\sqrt{13} - 2 - \abs*{\frac{\sqrt{13}}{6} + 2
- 2\sqrt{7}\paren*{1 + \delta V}}}/4
\DeclarePairedDelimiter to make \abs{} (i think it is even an example in the manual). It gives you a simpler interface to use.
\lvert and \rvert indicate "spacing as a left delimiter" and "spacing as a right delimiter," respectively. I agree it's counterintuitive, but there are times where I want the correct spacing, but to not scale the delimiters, such as $\abs{A_j}$ in text mode (if the delimiters scaled with the subscript, it would make the line too tall). So it's nice to have both options.
Nov 11, 2015 at 19:43
|-1| vs \lvert -1\rvert then you will see the significance