Hello Ross, <br><div class="gmail_quote"><br>thanks for the quick reply.<br><div class="gmail_quote"><div class="im"><div> </div><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
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> I'm looking for a way to draw arrows in xymatrix which stretch not over the whole distance between to nodes, but only over a certain percentage. I want to use this to draw 2-cells in commutative squares.<br>
<br>
</div>Xy-pic has a 2-cell feature, which lets you position<br>
a short double-arrow within a diagram, indicating<br>
the 2-cell nature of that portion of it.<br>
It was developed for, and used extensively in,<br>
Ross Street's book on "Quantum Groups".<br></blockquote></div><div><br>This is interesting, thanks. I had a look at the documentation, and now I have another question:<br><br>If I understand correctly, \xtwocell is a generalization of all of \drtwocell, \rrtwocell, ... . In the documentation, the format is specified as<br>
\xtwocell[ hop ]{ displace }...<br>In the hop argument, I can place the relative target just like for \ar, but what about the displace argument? I thought it served to move the source of the arrow, but that doesn't work. In the documentation it says "The displacement can be any string of valid xypic commands, but they must be enclosed within a group {...}.", but frankly I don't really understand what that means and what it's good for. I didn't find an example either. Well, at least it works when left empty.<br>
</div><div class="im"><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<br>
Does this not do the kind of thing that you want?<br>
Or do you want longer arrows, that adapt to the size<br>
of the square/rectangle or other polygonal area defined<br>
by the composition of arrows in the 2-cell?<br>
that is an awful lot harder, as you'll need to work out<br>
a way of specifying where to start and end the arrow.<br></blockquote></div><div><br>Well, specifying source and target of arrows hasn't been so difficult in my use cases, you can for example take the middle of a (possible invisible) arrow defined by something like:<br>
\ar@{}[dr]|{}="1".<br>(I found this trick on thte website of Aaron Lauda: <a href="http://www.math.columbia.edu/%7Elauda/xy/" target="_blank">http://www.math.columbia.edu/~lauda/xy/</a>)<br>This can be useful because then you can also draw bent 2-cells and in this way get a more three dimensional impression, for example to put 2-cells on the front and back of a cone. In this case it would be nice to say that the arrow should only be drawn in the interval between maybe 30% and 70% of the total distance.<br>
<br>Thanks a lot,<br><font color="#888888"><br>Jonas<br><br><br></font></div><div class="im"><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div><br>
><br>
> Until now, I have done this by drawing invisible frames around source and target nodes, as in the following example:<br>
> \[<br>
> \xymatrix{<br>
> FA<br>
> \ar[r]^{Ff}<br>
> \ar[d]_{\eta_A} &<br>
> FB<br>
> \ar[d]^{\eta_B}<br>
> \\<br>
> GA<br>
> \ar[r]_{Gf} &<br>
> GB<br>
> \\<br>
> %<br>
> \ar@{<=}"1,2"*+++\frm{};"2,1"*++\frm{}^{\eta_f}<br>
> }<br>
> \]<br>
> However, this seems overly complicated and has the disatvantage that the invisible frames reach in all directions, and so make the entire diagram bigger, resulting in too much space above and beneath the diagram in the document.<br>
><br>
> Is there a easier/better way to do this?<br>
><br>
> Thanks in advance,<br>
><br>
> Jonas<br>
<br>
<br>
</div>Hope this helps,<br>
<br>
Ross<br>
<br>
------------------------------------------------------------------------<br>
<font color="#888888">Ross Moore <a href="mailto:ross.moore@mq.edu.au" target="_blank">ross.moore@mq.edu.au</a><br>
Mathematics Department office: E7A-419<br>
Macquarie University tel: +61 (0)2 9850 8955<br>
Sydney, Australia 2109 fax: +61 (0)2 9850 8114<br>
------------------------------------------------------------------------<br>
<br>
<br>
<br>
</font></blockquote></div></div><br>
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