What is the "best LaTeX practices" for writing absolute value symbols? Are there any packages which provide good methods?
Some options include |x|
and \mid x \mid
, but I'm not sure which is best...
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Sign up to join this communityI 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}
\abs
yet. BTW, I like your "always is generally wrong" :-)
– Peter Grill
Jan 31 '12 at 23:57
\dfrac
in this case to make a larger fraction in inline mode. This is not normally recommended in inline mode as it breaks paragraph spacing. I will update the solution to remove that.
– Peter Grill
Feb 1 '12 at 0:16
*
-version for the automatic resizing macro: always using \left
and \right
is wrong, in general.
– egreg
Oct 15 '12 at 17:24
\abs
and \norm
which no one seems to have mentioned: since the |
symbol has special meaning in the makeidx
context, trying to enter terminology using a bare |
within \index{...}
will result in (delayed) errors and a lot of hair pulling for someone not really familiar with that usage. commands like the ones shown here (or even just bare \vert
, \Vert
or \mid
) is a lot safer and worth becoming familiar with.
– barbara beeton
Aug 19 '17 at 3:14
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}
The physics
LaTeX package also implements abs
and norm
:
\documentclass{article}
\usepackage{physics}
\begin{document}
\[ c = \abs{-c} \]
\[ \vu{a} = \frac{\vb{a}}{\norm{\vb{a}}} \]
\end{document}
A simple, LaTeX native way of doing this is by using the \|
delimiter, with the standard \left
and \right
modifiers (source).
For example:
\left\| \sum_{i=1}^{n} x^2 \right\|
gives
|
delimiter (without the preceding backslash) inserts a single vertical bar.
– pietrodn
Aug 11 '17 at 12:06
\|+a\|
, as you can see this is wrong, and thus generally users should not just use |...|
or \|...\|
as they may accidentally come into situations where this is wrong. I'll leave it as an exercise why this happens. Plus in your example the fences does not need to be that tall.
– daleif
Aug 11 '17 at 12:11
\|+a\|
the spacing appears to be wrong, but with \left\|+a\right\|
it appears to be fine.
– pietrodn
Aug 11 '17 at 12:19
\left
and \right
should only be added when actually needed (which is actually not often). My complain to your answer is that it is not good in general, for reasons that are explained in comments to other answers in this thread.
– daleif
Aug 11 '17 at 12:22
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[
%begin equation
\lVert w \rVert
%end equation
\]
\end{document}
For LyX users: maybe I have just overlooked how to do it correctly, but I couldn't find a way of doing this natively.
I thus used a 1x1-Matrix environment and set the kind to determinant. It might just be a hack, but it works fine in my usecase.
If you don't want to use any package, use \mid
.
\vert
doesn't require any package either, and the spacing isn't as awful as with \mid
.
– Phelype Oleinik
Feb 27 '20 at 23:26
\usepackage{amsmath}...\(\lvert x\rvert\)
;\mid
denotes a relation symbol and is wrong for the absolute value. – egreg Jan 31 '12 at 23:45$\usepackage{mathtools}...\DeclarePairedDelimiter{\vert}{\lvert}{\rvert}
as per your answer to a previous question? tex.stackexchange.com/a/42274/9757 – jamaicanworm Jan 31 '12 at 23:47\vert
is not a good choice, as it's already defined. – egreg Jan 31 '12 at 23:50|
symbol? – jamaicanworm Feb 1 '12 at 0:16|
, but in some situations a certain care is needed. For instance\(|{-1}|=1\)
without the braces would come out wrong, while\(\lvert-1\rvert=1\)
surely gives correct output. – egreg Feb 1 '12 at 0:22