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<DIV><SPAN class=593434006-06062006><FONT face="Comic Sans MS"
color=#000080>John,</FONT></SPAN></DIV>
<DIV><SPAN class=593434006-06062006><FONT face="Comic Sans MS" color=#000080>You
wrote :</FONT></SPAN></DIV>
<DIV><SPAN class=593434006-06062006><FONT face="Comic Sans MS"
color=#000080></FONT></SPAN> </DIV>
<DIV><SPAN class=593434006-06062006><FONT face=Arial size=2><EM>"Again looking
at log I saw that Cbc could work out that valid objective values had to be a
multiple of 0.1 so any solution has to be 0.1 better than previous. Going
back to original formulation and setting that value of 0.1 gave 31K nodes
but 305 seconds"</EM></FONT></SPAN></DIV>
<DIV><SPAN class=593434006-06062006><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=593434006-06062006><FONT face="Comic Sans MS" color=#000080>How
do you set that value of 0.1? Or have you added a constraint such as sum of
cijxij - 10 xn = 0 with xn a new integer variable.</FONT></SPAN></DIV>
<DIV><SPAN class=593434006-06062006><FONT face="Comic Sans MS"
color=#000080></FONT></SPAN> </DIV>
<DIV><SPAN class=593434006-06062006><FONT face="Comic Sans MS"
color=#000080>Best regards</FONT></SPAN></DIV>
<DIV><SPAN class=593434006-06062006><FONT face="Comic Sans MS"
color=#000080>Rolf</FONT></SPAN></DIV>
<DIV><SPAN class=593434006-06062006><FONT face="Comic Sans MS"
color=#000080></FONT></SPAN> </DIV>
<BLOCKQUOTE style="MARGIN-RIGHT: 0px">
<DIV></DIV>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left><FONT
face=Tahoma size=2>-----Original Message-----<BR><B>From:</B>
coin-discuss-bounces@list.coin-or.org
[mailto:coin-discuss-bounces@list.coin-or.org] <B>On Behalf Of </B>John J
Forrest<BR><B>Sent:</B> Saturday, June 03, 2006 16:02<BR><B>To:</B>
Discussions about open source software for Operations
Research<BR><B>Subject:</B> Re: [Coin-discuss] Suggestions on how to go about
tuning?<BR><BR></FONT></DIV><BR><FONT face=sans-serif size=2>Philip,</FONT>
<BR><BR><FONT face=sans-serif size=2>I said I would play about with your
problem and report on what I did and how I went about it :</FONT>
<BR><BR><FONT face=sans-serif size=2>All these experiments were with stand
alone solver - SOS is a bit trickier and I will get to that later. Also
symmetry breaking would help but I would need help in CglPreProcess and/or
pointers to relevant papers.</FONT> <BR><BR><FONT face=sans-serif size=2>The
first thing to do is solve the problem however slowly and look at log and
solution. Using defaults this took 1148 seconds and 150K nodes.
Looking at the log file it looked as if strong branching was not buying
very much. What was more interesting was that all variables took integer
values although only half were declared integer. Assuming this would
always be true I tried setting them all integer. This time strong
branching was kicking in and it took 5K nodes and 413 seconds. I also
saw that cuts and heuristics were not doing much good so switched them off.
</FONT> <BR><BR><FONT face=sans-serif size=2>Again looking at log I saw
that Cbc could work out that valid objective values had to be a multiple of
0.1 so any solution has to be 0.1 better than previous. Going back to
original formulation and setting that value of 0.1 gave 31K nodes but
305 seconds. Finally in this phase of tuning I tried switching off
strong branching as my hunch was that it might cost too much for the effect
gave an increase in nodes to 38K but the time dropped to 233 seconds.</FONT>
<BR><BR><FONT face=sans-serif size=2>Further ideas such as just having some
(but not the original set) variables integer gave various perturbations on
time and nodes but no significant improvement.</FONT> <BR><BR><FONT
face=sans-serif size=2>I have started looking at SOS possibilities but am not
far along. </FONT> <BR><BR><FONT face=sans-serif size=2>Basically I use
multiple runs and an editor and grep to try and get a feel for problem.</FONT>
<BR><BR><FONT face=sans-serif size=2>John
Forrest</FONT></BLOCKQUOTE></BODY></HTML>