[Xy-pic] Fwd: xypic question

[Ross Moore]

Hello Richard,

On 14/09/2010, at 5:18 AM, Richard Hain wrote:

> 
> Hi Ross,
> 
> I am sorry to bother you with this xypic question, but there is
> something that I just cannot get to work properly (and suspect that
> this is because there is a bug). See the attached tex file.


Try this:

\def\cG{\mathcal G}
\def\cP{\mathcal P}
\def\g{\mathfrak g}
\def\p{\mathfrak p}
\def\nab{\mathrm{nab}}
\def\Hnab{H_\nab}
\newcommand\Gr{\operatorname{Gr}}

$$
\xymatrix{
\Hnab^1 \save !L(.6)="Hnab"; "Hnab",\ar@(ul,dl)"Hnab"_{{H^1(\g,\Gr^W_{-N}\p)}}\restore
\ar[r]^-(.55)\pi &
\Hnab^1(\cG,\cP/W_{-N}) \ar[r]^(.55){\delta} & H^2(\g,\Gr^W_{-N}\p)
}
$$

Adjust the (.6) factor to suit your own taste.

The problem is that you want to change the end \POSs of the arrow
from what they would normally be, inherited from the cell contents.
You need a \save ... \restore  sequence to do this,
and also need to set the target of the arrow accordingly, 
rather than use [] which refers back to the cell again.

This also works, without requiring a new named \POS :

$$
\xymatrix{
\Hnab^1 \save !L(.6);p,\ar@(ul,dl)p_{{H^1(\g,\Gr^W_{-N}\p)}}\restore
\ar[r]^-(.55)\pi &
\Hnab^1(\cG,\cP/W_{-N}) \ar[r]^(.55){\delta} & H^2(\g,\Gr^W_{-N}\p)
}
$$


> 
> Best, Dick
> <ross.tex>


Hope this helps,

	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
------------------------------------------------------------------------




------------------------------------------------------------------------
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
------------------------------------------------------------------------