<br><font size=2 face="sans-serif">Paulo,</font>
<br>
<br><font size=2 face="sans-serif">To build a robust parametric solver
is difficult as you have to avoid degeneracy etc. It looks as if
the code thinks it is making zero moves so is slightly perturbing the problem
to try and make some progress. The fix you are using will reset these
tiny perturbations. If you don't need speed then I would just use
plain primal after updating objective and if you have a zero move then
add a small amount anyway before doing primal.</font>
<br>
<br><font size=2 face="sans-serif">John Forrest</font>
<br>
<br>
<br>
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<td width=40%><font size=1 face="sans-serif"><b>"Paulo J. S. Silva"
<pjssilva@ime.usp.br></b> </font>
<br><font size=1 face="sans-serif">Sent by: coin-lpsolver-bounces@list.coin-or.org</font>
<p><font size=1 face="sans-serif">03/08/2005 01:21 PM</font>
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<div align=right><font size=1 face="sans-serif">To</font></div>
<td valign=top><font size=1 face="sans-serif">coin-lpsolver@list.coin-or.org</font>
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<td>
<div align=right><font size=1 face="sans-serif">cc</font></div>
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<td>
<div align=right><font size=1 face="sans-serif">Subject</font></div>
<td valign=top><font size=1 face="sans-serif">Re: [Coin-lpsolver] Parametric
Analysis using CLP + OSI</font></table>
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<br><font size=2><tt>Ops...<br>
<br>
I am still having problems with the parametric analysis code. It looks<br>
like John changes to primalPivotResult still don't refresh everything<br>
needed.<br>
<br>
For now my code may face numerical problems if I update the objective<br>
function before primalPivotResult. After many pivots the function is<br>
changing a little the reduced costs (it should remain the same as I said<br>
in the last e-mail). The difference is up to 1.0e-8, but this is enough<br>
for the code to detected incorrectly unboundedness of the problem.<br>
<br>
If I move the objective function after the primalPivotResult everything<br>
works. It also work if I leave the objective update before the pivot<br>
function but call<br>
<br>
s.disableSimplexInterface()<br>
s.enableSimplexInterface(True)<br>
<br>
after the pivot. I believe this two calls refresh some data.<br>
<br>
Unfortunately, I have to give a seminar in two days and I still don't<br>
have the slides. So I wont be able to work for two days on this. When I<br>
come back I'll look at the paraobj code John added to the unit tests to<br>
see if I can reproduce the error my reading the MPS file with the<br>
problem description.<br>
<br>
Best,<br>
<br>
Paulo<br>
<br>
-- <br>
Paulo José da Silva e Silva <br>
Professor Assistente do Dep. de Ciência da Computação<br>
(Assistant Professor of the Computer Science Dept.)<br>
Universidade de São Paulo - Brazil<br>
<br>
e-mail: pjssilva@ime.usp.br Web: http://www.ime.usp.br/~pjssilva<br>
<br>
Teoria é o que não entendemos o (Theory is something we don't)<br>
suficiente para chamar de prática. (understand well enough to call) <br>
(practice)<br>
<br>
<br>
<br>
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</tt></font>
<br>