[Tex/LaTex] Absolute Value Symbols

math-modesymbols

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…

Best Answer

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:

enter image description here

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}

Related Solutions

[Tex/LaTex] Too long/short pipe (absolute value) in math mode with certain letters

I was able to use my scalerel package to hopefully give you what you want (scalerel was just sent to CTAN today, so until it propagates, you can find the style listing at How to horizontally merge two symbols?).

Using that package's features, my first cut was to create a command \myabs, which places abs bars around anything. It will stretch the size of the bars exactly to the argument. The downside of this first attempt is that you may have preferred the bars to extend a bit above and below the object being surrounded (addressed later in this answer). Here's the code for the first approach:

\documentclass{article}
\usepackage{scalerel}
\usepackage{mathtools}

\begin{document}
% [METHOD USED IN ORIGINAL QUESTION CODE HERE, REMOVED FROM THIS LISTING]
\newcommand\myabs[1]{%
  \setbox1\hbox{$#1$}%
  \stretchrel{\lvert}{\usebox1}\stretchrel*{\lvert}{\usebox1}%
}

\[ \myabs{\vec{k}}~~\myabs{\vec{x}}~~\myabs{\vec{A}}~~\myabs{\vec{q}} \]

\end{document}

and here's the output, as compared to your original

enter image description here

However, to answer ralfix's request to extend the vertical line a bit above and below the surrounding object, I just used the \addvbuffer routine from the verbatimbox package, setting the top and bottom add-on to 2pt:

\documentclass{article}
\usepackage{scalerel}
\usepackage{mathtools}
\usepackage{verbatimbox}

\setlength\boxtopsep{2pt}
\setlength\boxbottomsep{2pt}
\newcommand\myabs[1]{%
  \setbox1\hbox{$#1$}%
  \setbox2\hbox{\addvbuffer{\usebox1}}%
  \stretchrel{\lvert}{\usebox2}\stretchrel*{\lvert}{\usebox2}%
}

\begin{document}
\[ \myabs{\vec{k}}~~\myabs{\vec{x}}~~\myabs{\vec{A}}~~\myabs{\vec{q}} \]
\end{document}

enter image description here

But egreg commented that the height of the abs bar should not change with the argument. If that is the preferred embodiment of abs, then scalerel can fix that too:

\documentclass{article}
\usepackage{scalerel}

\def\lvert{|}
\begin{document}
METHOD 2: FIXED EXTENT
\newsavebox\mybox
\savebox{\mybox}{$\stretchrel*{|}{\rule[-.6ex]{0ex}{3ex}}$}
\def\myabs#1{\usebox\mybox#1\usebox\mybox}

\[ \myabs{\vec{k}}~~\myabs{\vec{x}}~~\myabs{\vec{A}}~~\myabs{\vec{q}} \]
\end{document}

enter image description here

[Tex/LaTex] absolute value in numerator of fraction

Make sure the \abs macro is defined.

\documentclass{article}
\usepackage{mathtools}           % for '\DeclarePairedDelimiter' macro
\DeclarePairedDelimiter{\abs}{\lvert}{\rvert} % define '\abs' macro
\begin{document}
$\frac{\abs{\lambda_f}}{8\pi^2}$\quad $\dfrac{\abs{\lambda_f}}{8\pi^2}$
\end{document}

Best Answer

Related Solutions

[Tex/LaTex] Too long/short pipe (absolute value) in math mode with certain letters

[Tex/LaTex] absolute value in numerator of fraction

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