Absolute Value Symbols
I have been using the code below using \DeclarePairedDelimiter
from the mathtools
package.
Since I don't think I have a case where I don't want this to scale based on the parameter, I make use of Swap definition of starred and non-starred command so that the normal use will automatically scale, and the starred version won't:
If you want it the other way around comment out the code between \makeatother...\makeatletter
.
\documentclass{article}
\usepackage{mathtools}
\DeclarePairedDelimiter\abs{\lvert}{\rvert}%
\DeclarePairedDelimiter\norm{\lVert}{\rVert}%
% Swap the definition of \abs* and \norm*, so that \abs
% and \norm resizes the size of the brackets, and the
% starred version does not.
\makeatletter
\let\oldabs\abs
\def\abs{\@ifstar{\oldabs}{\oldabs*}}
%
\let\oldnorm\norm
\def\norm{\@ifstar{\oldnorm}{\oldnorm*}}
\makeatother
\newcommand*{\Value}{\frac{1}{2}x^2}%
\begin{document}
\[\abs{\Value} \quad \norm{\Value} \qquad\text{non-starred} \]
\[\abs*{\Value} \quad \norm*{\Value} \qquad\text{starred}\qquad\]
\end{document}
Note if you just use |
you get mathord spacing, which is different from the spacing you'd get from paired mathopen/mathclose delimiters or from \left/\right
even if \left/\right
doesn't stretch the symbol. Personally I prefer the left/right spacing from mathinner here (even if @egreg says I'm generally wrong:-)
\documentclass{amsart}
\begin{document}
$ \log|x||y|b $
$ \log\left|x\right|\left|y\right|b $
$ \log\mathopen|x\mathclose|\mathopen|y\mathclose|b $
\end{document}
One can also use commath
package.
\documentclass{article}
\usepackage{commath}
\begin{document}
\[ \norm{a \vec{u}} = \abs{a} \, \norm{\vec{v}} \]
\end{document}