<br><font size=2 face="sans-serif">Kirsten,</font>
<br>
<br><font size=2 face="sans-serif">It is fairly obvious that you would
get the first "access violation reading location". Without
knowing more about your driver I can't say much about the second one.</font>
<br>
<br><font size=2 face="sans-serif">Fixing many variables could easily allow
CglProbing to find that the problem is infeasible and then this can happen.
I have modified code in branches/devel to trap this before error
message.</font>
<br>
<br><font size=2 face="sans-serif">Try with no cut generators at all.</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>"Wiebe Kirsten (Stud.
FdEWB)" <K.Wiebe@Student.Unimaas.NL></b> </font>
<br><font size=1 face="sans-serif">Sent by: coin-discuss-bounces@list.coin-or.org</font>
<p><font size=1 face="sans-serif">07/14/2006 08:04 AM</font>
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<div align=center><font size=1 face="sans-serif">Please respond to<br>
Discussions about open source software for Operations Research
<coin-discuss@list.coin-or.org></font></div></table>
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<div align=right><font size=1 face="sans-serif">To</font></div>
<td><font size=1 face="sans-serif">"Discussions about open source
software for Operations Research" <coin-discuss@list.coin-or.org></font>
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<div align=right><font size=1 face="sans-serif">cc</font></div>
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<div align=right><font size=1 face="sans-serif">Subject</font></div>
<td><font size=1 face="sans-serif">[Coin-discuss] Solving ILP within B&B
framework</font></table>
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<br><tt><font size=2>Hello everyone,<br>
I'm currently writing my master thesis in operations research about rankings
in tournaments using the linear ordering polytope. My idea is to find all
Slater solutions for that tournament with the help of a branch and bound,
where, in each node of the b&b tree, the ILP of the linear ordering
polytope is solved to optimality. For that I start with solving the ILP
once to optimality and then "going up" in the tree fixing all
variables above the currently processed node to what they were before (in
the current solution of the ILP) and the variable that is branched on in
that node to its complement, i.e. to (1 - (what is was before)). I implemented
a function that detects 3-cycles, i.e. infeasibility if the transitivity
is not satisfied; but it seems that there is still something going wrong.
For a little instance where there are 4 participants for the tournament
and hence 6 variables representing the binary relations the algorithm,
that until now is simply supposed to go up in the b&b tree once, is
working ok. In a larger instance, with 40 participants and hence 780 binary
relations, I get that error message about "Access violation reaing
location ..." after 33 iterations and my output says:<br>
<br>
Clp6002E 192 bad bound pairs or bad objectives were found - first at R9884<br>
Clp0004I Stopped due to errors - objective value 0<br>
Cgl0000I Cut generators found to be infeasible!<br>
<br>
The error message occurs where "model" is defined (model is the
object with which I can define the branching method and node comparison
and add cuts:<br>
<br>
solver1=getModelForILP();<br>
// Use Preprocessing of Coin<br>
solver1.initialSolve();<br>
solver2=&solver1;<br>
solver2=PreProcess.preProcess(solver1,true,5);<br>
model = new CbcModel(*solver2); <-- HERE IS THE ERROR<br>
<br>
Does that mean that I cannot use the CoinOR cuts here, or is already something
wrong with using the preprocessing?<br>
<br>
I think it is about the preprocessing, because when I include<br>
<br>
if(solver2 == NULL)<br>
{<br>
cout << "Preprocessing did not work, node skipped\n";<br>
return 1;<br>
}<br>
<br>
before "model = new CbCModel(*solver2);" and hence return to
main to continue without processing the node, the algorithm continues until
iteration 95, but then there is again the error message about "access
violation reading location..." when the program tries to access the
column solution of column 423 (the variable that is branched on there).
When debugging and looking until which column there are solutions I get
that there are only solutions until column 218. In the beginning I had
that problem already at iteration 33 and iteration 91, but that is not
the case anymore and I just don't get why...<br>
<br>
Greetz<br>
Kirsten<br>
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