<br><font size=2 face="sans-serif">Ojas,</font>
<br>
<br><font size=2 face="sans-serif">I will have to run those problems to
check but it is probable that the clp executable is being clever about
algorithms and initial solutions. You should be able to get same
results with ClpSimplex::initialSolve by setting parameters.</font>
<br>
<br><font size=2 face="sans-serif">Would it be useful if I worked on the
interface and documentation for part of my DIMACS presentation?</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>Ojas Parekh <ojas@mathcs.emory.edu></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">05/01/2006 10:07 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">coin-lpsolver@list.coin-or.org</font>
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<td>
<div align=right><font size=1 face="sans-serif">cc</font></div>
<td><font size=1 face="sans-serif">Sebastien Siva <ssiva@emory.edu>,
Cynthia A Phillips <caphill@sandia.gov></font>
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<td>
<div align=right><font size=1 face="sans-serif">Subject</font></div>
<td><font size=1 face="sans-serif">[Coin-lpsolver] OsiClp/ClpSimplex/clp
performance disparity</font></table>
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<br>
<br>
<br><tt><font size=2>Hi,<br>
<br>
We've observed appreciable disparities in the performance of <br>
OsiClpSolverInterface->initialSolve(), ClpSimplex->initialSolve(),
<br>
and the clp executable program. In particular here are some of our
<br>
observed running times on instances from well-known collections:<br>
<br>
collection/file
clp exec. ClpSimplex OsiClp<br>
----------------------------- --------- ----------
------<br>
Linderoth-MIP/dano3_4.mps 57.78
151.99 145.44<br>
Linderoth-MIP/neos-520729.mps 7.70
20.46 20.50<br>
Linedroth-MIP/qap10.mps 4.00
3.90 51.51<br>
COIN/Mps/Big/mkc7.mps 21.15
169.08 165.12<br>
<br>
All numbers represent seconds on a 2.2Ghz dual core Opteron running a <br>
SUSE x86_64 Linux distribution using a CVS build of COIN-OR no older <br>
than a few weeks. We've also observed comparable ratios on Solaris
<br>
and PPC Mac OS X machines. We passed no parameters to the clp <br>
executable other than the file name and used the following code for <br>
the object oriented interfaces:<br>
<br>
ClpSimplex model;<br>
model.readMps(argv[1]);<br>
model.initialSolve();<br>
<br>
and<br>
<br>
OsiClpSolverInterface si;<br>
si.readMps(argv[1]);<br>
si.initialSolve();<br>
<br>
We have larger instances particular to our application (Sandia Labs' <br>
PICO combinatorial optimization engine) that have exhibited similar <br>
behavior: the clp executable performs an order of magnitude better.
<br>
We have tried experimenting with ClpSolve parameters and writing a <br>
simple heuristic to mimic the clp executable but have been <br>
unsuccessful in consistently obtaining comparable performance. <br>
Before proceeding any further I thought it would be a good idea to <br>
ask the following questions here:<br>
<br>
(1) Does the clp executable do any extra preprocessing or <br>
presolving? Do you think the gap is explained only by the way in
<br>
which the three interfaces each set their parameters? If so, which
<br>
parameters are especially critical for the problems above?<br>
<br>
(2) I have explored the source code; however, I was wondering if <br>
there was any documentation that speaks specifically to the <br>
differences in (in philosophy of) the three interfaces.<br>
<br>
(3) PICO currently exclusively relies on the OsiClp interface. I
<br>
understand that I can use the getModelPtr() method to call <br>
ClpSimplex's version of initialSolve(). Is there callable access
to <br>
the code that the clp executable uses?<br>
<br>
Thanks!<br>
-Ojas<br>
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