[Xy-pic] Conflict between xymatrix and 12pt ?

[Ross Moore]

Hi Robert,

On 01/11/2010, at 6:34 AM, Robert Seely wrote:

> It seems there may be a conflict between xymatrix and 12pt style, as
> indicated by the following sample file:
> 
> %%%%%%%%%%%%%%%%%%
> 
> \documentclass[12pt]{article}
> 
> \input xy
> \xyoption{all}
> 
> \begin{document}
> 
> \[
> \xymatrix at R=10pt at C=5pt{ x_1 & & x_2  \\
>      & *-[o]{\bullet} \ar@{-}[ul] \ar@{-}[ur]     \\
> }
> \]
> 
> \end{document}
> 
> %%%%%%%%%%%%%%%%%%%%
> 
> This terminates with an error message:
> 
> Xy-pic Warning: division overflow [testac:13].
> 
> ! Arithmetic overflow.
> <recently read> \quotPTK@
> 
> HOWEVER: this doesn't appear to be a problem with xypic in general,
> since if one uses Michael Barr's diagxy "front-end" to xypic, all is
> fine.  Eg, the following file TeXs just fine.

The problem is caused by your use of:

> *-[o]{\bullet}


presumably to reduce the size of the <object> with
the bullet.  Change this to:  *=0[o]{\bullet}
and the problem goes away.

I'm guessing that  *- subtracts too much (or too little), 
leaving a negative width or height, or some tiny size 
for the margin when you might as well have none at all.

Certainly it is a subtle problem, requiring further
tracing to get to the real nature of the difficulty.

> 
> %%%%%%%%%%%%%%%%%%%%%
> 
> \documentclass[12pt]{article}
> 
> \input xy
> \xyoption{all}
> \input diagxy
> \newdir{O}{\object{\bullet}}
> 
> \begin{document}
> 
> $$\bfig
> \morphism(0,0)/-O/<175,-200>[x_1`;]
> \morphism(350,0)/-O/<-175,-200>[x_2`;]
> \morphism(600,0)/-O/<0,-200>[x_3`;]
> \efig$$
> 
> \end{document}
> 
> %%%%%%%%%%%%%%%%%%%%%
> 
> 
> Hoping for a "simple solution",
> best regards, Robert (Seely)
> 
> 
> -- 
> <rags at math.mcgill.ca>
> <www.math.mcgill.ca/rags>


Hope this helps, and thanks for the report,

	Ross

------------------------------------------------------------------------
Ross Moore                                       ross.moore at mq.edu.au 
Mathematics Department                           office: E7A-419      
Macquarie University                             tel: +61 (0)2 9850 8955
Sydney, Australia  2109                          fax: +61 (0)2 9850 8114
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