arrows
I want to draw 2 parallel arrows in the xy matrix environment.
Basically instead of the standard arrow (\ar[r]), I want to have something like \begin{smallmatrix}\longrightarrow\\\longrightarrow\end{smallmatrix}.
I tried leaving the arrow blank and just writing
$$\xymatrix{\begin{smallmatrix}\longrightarrow\\\longrightarrow\end{smallmatrix}}$$, but its not working.
Edit: I need it to write two simplicial objects and arrows between them.
It's not so hard.
Dig a hole:
\xymatrix{ \ar[dr]|\hole & \\ \ar[ur] & }
Calculate the intersection point and dig a hole:
\xymatrix{ \ar[drr]|!{[d];[r]}\hole & & \\ \ar[ur] & & }
I personally use :
\documentclass{article}
\usepackage[all]{xy}
\begin{document}
\[
\xymatrix@1{A\, \ar@{}[r]|-*[@]{\subset} & B}
\]
\end{document}
It's very simple and I guess it can look weird if the space between entries is too big, but I feel it the best way, enlarged subset symbols are just awful.
Maybe with a little more skill in xy-pic constructions, you can arrange to slightly rescale the symbol depending on the space between entries. By hand, it's possible for sure, but I guess it would be possible to do that automatically too.
Best Answer
this coding works.
it's necessary to offset the arrows explicitly from the usual axis alignment in order for them to appear separately. you might prefer different values for the separation, but it seems reasonable to offset them by an equal amount plus/minus.
i didn't find the exact coding in the manual, but there were some examples that looked promising. this solution was arrived at after some experimenting.