symbolssyntax
I want to write in math mode that something is compared to something else. It is, I want to say that both quantities have the same order of magnitude. What symbol should I use?
\documentclass{article}
\begin{document}
\[
A \approx B
\]
\end{document}
Or something else?
What you describe seems similar to the nonmonotonic inference relation symbol used in this paper. The main difference being that this a small space between the two characters, which I think actually looks better than having them touch.
\documentclass{article}
\newcommand*{\nc}[2]{#1\mathbin{\left| \sim \vphantom{#1#2} \right.}#2}%
\begin{document}
$\nc{A}{B} \qquad \nc{\frac{A}{C}}{B}$
\end{document}
Update: Here is a version where both the straight and wavy line are re-sized and the two symbols touch:
I have used \scalebox from the \graphicx package to resize the symbols (resize horizontally for the wavy line and vertically for the vertical bar) based on the height of the operands on either side. The \mathrlap is obtained from a TUGboat 22 article entitled a complement to \smash, \llap, and \rlap. I am not an expert in the use of the rlap type command, so perhaps some of the resize code could be simplified. I also used pgf to do the math, and this is probably overkill but I am more familiar with that then doing math in plain TeX.
\documentclass[border=2pt]{standalone}
\usepackage{amsmath}% only needed for \dfrac
\usepackage{graphicx}% needed for \scalebox
\usepackage{pgf}% needed for the math calculations
% http://math.arizona.edu/~aprl/publications/mathclap/
\def\mathrlap{\mathpalette\mathrlapinternal}%
\def\mathrlapinternal#1#2{\rlap{$\mathsurround=0pt#1{#2}$}}%
\makeatletter
\newdimen\@mydimen%
\newdimen\@myHeightOfBar%
\settoheight{\@myHeightOfBar}{$|$}%
\newcommand{\SetScaleFactor}[1]{%
\settoheight{\@mydimen}{#1}%
\pgfmathsetmacro{\scaleFactor}{\@mydimen/\@myHeightOfBar}%
}%
\newcommand*{\Scale}[2][3]{\scalebox{#1}{\ensuremath{#2}}}%
\newcommand*{\nct}[2]{%
\SetScaleFactor{\vphantom{\ensuremath{#1#2}}}% Compute scale to be applied
#1%
\mathrel{\Scale[\scaleFactor]{|\mathrlap{\kern-0.48ex\sim}\hphantom{\kern-0.41ex\sim}}}%
#2%
}%
\begin{document}
$\nct{a}{b} \qquad \nct{\frac{A}{C}}{B} \qquad \nct{\dfrac{A}{C}}{B}$
\end{document}
An enhanced version of this solution that allows you to specify a character to be placed above and below the wavy line is available at the follow-up question: Symbol for skeptical consequence that matches the turnstile package
You could use this little snippet which defines \textify. The control sequence \textify takes another control sequence (for instance \exists) and wraps it into \ensuremath{…}.
I don't think that one needs to go through all the \GlobalLetLtxMacro and \protected\gdef hassle for simple things like \exists, which is only a \mathchar, but this should cover all weird edge cases.
N.B.: The \macro in \textify\macro may not take any mandatory arguments. Optional arguments will output as their default value. If the macro you want to textify needs any arguments a more complicated approach is needed.
\documentclass{article}
\usepackage{letltxmacro}
\newcommand\textify[1]{%
\expandafter\GlobalLetLtxMacro\csname textify@\string#1\endcsname#1%
\protected\gdef#1{\ensuremath{\csname textify@\string#1\endcsname}}%
}
\textify\exists
\textify\forall
\begin{document}
\exists $\exists$
\forall $\forall$
\end{document}
For reference, a non-letltxmacro and non-protected version of \textify would read
\newcommand\textify[1]{%
\global\expandafter\let\csname textify@\string#1\endcsname#1%
\gdef#1{\ensuremath{\csname textify@\string#1\endcsname}}%
}
which of course doesn't require the letltxmacro package.
Best Answer
The list of symbols on Wikipedia suggest to use
\sim(for “poorly approximates”). However one should always keep in mind that there's no world authority for mathematical symbols, so different fields could use different symbols.In order to be as independent as possible from a particular choice, type
and use
\soomin your document. It will be easy to change the symbol by just modifying this definition.Use the command name you prefer, instead of
\soom, of course.