geometrysymbols
I need a way of encoding the geometry line symbol. $\overline{AB}$ gives me the line segment symbol and $\overrightarrow{AB}$ gives me the ray symbol, I need a way to get a bar over the letters that has arrows on both ends. $\overrightleftarrow{AB}$ does not work.
Thanks!
Most mathematical symbols allow negation via the \not prefix. For example, consider the look of
f(x)\not=\frac{-b\pm\sqrt{b^2-4ac}}{2a}\not\to\mathcal{A}
There is also centernot which looks similar to \not= in the above case, yet different (perhaps not-so-good) from \not\to.
Alternatively, Scott Pakin's Comprehensive Symbol List has a vast amount of mathematical symbols and their associated fonts/package inclusions.
Basically you have to just do it by eye, as you have done. TeX has no information about the line widths (or the shape of the glyph at all). Even if you look in to the type1 or metafont sources of the font and find out the original design widths, you can not ensure at small sizes that you get exactly the same width using a rule, as the lines in the font are subject to the renderer's font hinting mechanism which may snap the lines on to pixel boundaries, whereas rules are drawn by different mechanisms and not subject to the same hinting.
You might do better just offsetting the same character so the rules are subject to the same hinting:
\documentclass{article}
\usepackage{graphicx}
\newcommand{\sqqcup}{\,{{\sqcup}\hspace*{-0.6em}\raisebox{-0.25ex}{--}}\;}
\def\xsqqcupb#1#2{\mathbin{\rlap{\raisebox{.15em}{$#1#2$}}{#2}}}
\def\sqqcupb{\mathpalette\xsqqcupb\sqcup}
\begin{document}
\[
\scalebox{8}{$a \sqqcup b$}
\]
\[
\scalebox{8}{$a \sqqcupb b$}
\]
\end{document}
Update:
As discussed in the comments it would be possible to hide the extra height with a coloured rule, but beware that the colour may hide more than you intend 9note the top bar of the fbox in the modified example)
\documentclass{article}
\usepackage{graphicx,color}
\newcommand{\sqqcup}{\,{{\sqcup}\hspace*{-0.6em}\raisebox{-0.25ex}{--}}\;}
\def\xsqqcupb#1#2{\rlap{\raisebox{.15em}{$#1#2$}}{#2}}
\def\sqqcupb{\mathbin{\mathpalette\xsqqcupb\sqcup}}
\def\xsqqcupc#1#2{\smash{\rlap{\raisebox{.15em}{$#1#2$}}\rlap{\color{white}\rule[.3em]{0.7em}{1.1ex}}}{#2}}
\def\sqqcupc{\mathbin{\mathpalette\xsqqcupc\sqcup}}
\begin{document}
\fbox{\scalebox{8}{$a \sqqcup x$}}
\bigskip
\fbox{\scalebox{8}{$a \sqqcupb x$}}
\bigskip
\fbox{\scalebox{8}{$a \sqqcupc x$}}
\end{document}
Best Answer
Use
$\overleftrightarrow{AB}$with themathtoolsoramsmathpackages.