# [Xy-pic] bizarre bug

Ross Moore ross at ics.mq.edu.au
Wed Oct 31 20:16:23 CET 2007

Hi Jürgen,

On 31/10/2007, at 8:22 PM, Juergen Koslowski wrote:

> Dear Ross,
>
> Well, I took all extraneous packages off and still get the behaviour
> that number subscripts suppress the second circle, while letter
> subscripts allow it.  It does not matter, in which order the nodes
> appear.  This happens on two different machines.  If you don't see
> this
> behaviour, that would be really interesting!  I'll ask our TeX-Guru to
> run the example as well.

This seems to be just a quirk in the way the circle sizes are chosen.
You are always getting 2 circles drawn, but sometimes the radius is
the same, so you see it as being only 1 circle.

>
> \documentclass{article}

Try using
\documentclass[11pt]{article}

> \usepackage[matrix,frame]{xy}
> \def\rin#1{**{+<3 pt>[o][F]}#1}

or make this a bit bigger:

\def\rin#1{**{+<3.5pt>[o][F]}#1}

>
> \begin{document}
>
> $\xymatrix at C+8 pt@*[F]@*[o]@*+<3 pt>{ > \rin q_0 > &\rin q_n > } >$
>
> $\xymatrix at C+8 pt@*[F]@*[o]@*+<3 pt>{ > \rin q_n > &\rin q_4 > } >$
>
> \end{document}
>
> -- Jürgen

Another way to see that there is really no problem is to
use the PS backend:

\usepackage[dvips,ps,matrix,frame]{xy}

This will use elliptical frames chosen according to
the exact size (i.e. height & width) of the object being
framed. Now you always get the 2 ellipses, but each is
object is slightly different, perhaps annoyingly so.

you would do better to set a constant size before adding
the circular frames.

Note that without the PS backend, Xy-pic chooses circular
frames from a discrete set of sizes, using font pieces
from the XYCIRC10 font.

So for  q_0 in 10pt the size chosen for the 2 circles
just happens to be the same, whereas for  q_n  there
is enough difference to get different circles.

>
> --
> Juergen Koslowski               If I don't see you no more on this
> world
> ITI, TU Braunschweig               I'll meet you on the next one
> koslowj at iti.cs.tu-bs.de               and don't be late!
> http://www.iti.cs.tu-bs.de/~koslowj      Jimi Hendrix (Voodoo
> Child, SR)

Hope this helps,

Ross

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Ross Moore                                         ross at maths.mq.edu.au
Mathematics Department                             office: E7A-419
Macquarie University                               tel: +61 +2 9850 8955
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