<br><font size=2 face="sans-serif">Anureet,</font>
<br>
<br><font size=2 face="sans-serif">I am busy at present, but it might be
useful to do what you suggest. At present solvers just return whatever
ray they have, but it would be possible to change code so that if more
than one ray was asked for then the original + better rays would be returned.
It would be more useful if this facility was done by the base OsiSolverInterface
class rather than OsiClp or OsiXpr etc.</font>
<br>
<br><font size=2 face="sans-serif">John Forrest</font>
<br>
<br>
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<td width=40%><font size=1 face="sans-serif"><b>Anureet Saxena <anureet@yahoo.com></b>
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<br><font size=1 face="sans-serif">Sent by: coin-lpsolver-bounces@list.coin-or.org</font>
<p><font size=1 face="sans-serif">10/25/2006 07:34 PM</font>
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<div align=right><font size=1 face="sans-serif">To</font></div>
<td><font size=1 face="sans-serif">John J Forrest/Watson/IBM@IBMUS</font>
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<div align=right><font size=1 face="sans-serif">cc</font></div>
<td><font size=1 face="sans-serif">coin-lpsolver@list.coin-or.org, anureet@yahoo.com</font>
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<div align=right><font size=1 face="sans-serif">Subject</font></div>
<td><font size=1 face="sans-serif">Re: [Coin-lpsolver] getPrimalRay()</font></table>
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<br><tt><font size=2>hi John,<br>
<br>
Thanks for your reply.<br>
Setting OsiDoPresolveInInitial to false (using setHintParam()) does switch
off<br>
the presolve, but it does not resolve the problem. The extreme ray returned<br>
still has the same large numbers.<br>
<br>
Scaling is indeed a solution but it is not very good and affects other
parts of<br>
the code, as you pointed out.<br>
<br>
I was wondering if there is a way to extract extreme rays from the tableau<br>
using the textbook method of using columns with no pivotable row. The good<br>
thing about that approach is that if the problem has numerically stable
basis,<br>
then the extreme ray will also have reasonably sized coefficients. Please<br>
excuse me if this is too much to ask frm the current implementation in
OsiClp,<br>
as I am not at all familiar with the details.<br>
<br>
If anyone has worked with extracting extreme rays using OsiClp and has
an<br>
approach to avoid very large numbers, please let me know.<br>
<br>
Thanks for your replies,<br>
Regards,<br>
Anureet Saxena<br>
<br>
<br>
<br>
Anureet Saxena<br>
anureet@cmu.edu<br>
anureet@yahoo.com<br>
<br>
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