Originally posted by: JorisK

Dear,

Using the Java programming interface of CPLEX, I've built a rather complicated MIP model. The model is initialized with a feasible initial solution by invoking the addMIPStart(vars, values, IloCplex.MIPStartEffort.CheckFeas); function. However, when solving the MIP problem, I get the following error:

Warning: No solution found from 1 MIP starts.

which implies that either my initial solution is not feasible, or my model cuts of feasible solutions. In either case I would like to find the constraints which cut of the initial solution. According to the documentation (User's Manual for CPLEX > Refining a conflict in a MIP start) there are multiple approaches to find a minimal conflict set of constraints. I first exported the MIP model to a file using the cplex.exportModel("test.lp"); function. Additionally, I exported the MIP start via the function cplex.writeMIPStart("mipStart.mst"); (see attached documents).

Finally, I tried to determine the conflict using the Interactive Optimizer as suggested in this thread: http://www.ibm.com/developerworks/forums/thread.jspa?threadID=363875

CPLEX> read test.lp
Problem 'test.lp' read.
Read time = 0.03 sec.
CPLEX> read mipStart.mst
MIP start file 'mipStart.mst' read.
CPLEX> conflict 1

Refine conflict on 3000 members...

Iteration Max Members Min Members
1 0 0

Minimal conflict: 0 linear constraint(s)
0 lower bound(s)
0 upper bound(s)
Conflict computation time = 0.02 sec. Iterations = 1

Apparently the approach suggested in the previous thread does not work (anymore) as I do not get any conflicts, or am I doing something wrong?
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Originally posted by: T_O

Your MIPStart does not satisfy constraint IloC2849 as all its variables are 0. To find this out, I fixed all bounds to your MIPStart and ran the conflict refiner.

Best regards,
Thomas
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Originally posted by: JorisK

Thank you for the effort!
Out of curiosity: how did you fix all bounds to my MIPStart values so quickly? Is there some function within cplex which can do that, or did you write a script for that? Surely, you did not assign nearly 3000 variables manually :)
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Originally posted by: T_O

I used search-and-replace in Notepad++ a few times to make the MIPstart look like bounds of an LP-file. Then it was just a simple copy&paste.

Best regards,
Thomas
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Originally posted by: SystemAdmin

On a Linux command line things were even easier:

sed -n -e 's,^.*name="\([^"]*\)".*value="\([^"]*\)".*$,\1 = \2,p' mipStart.mst

Add the output of that at the end of the "Bounds" section in the LP file and your done.
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Originally posted by: SystemAdmin

The input sequence to the interactive looks correct.
I can reproduce the problem here and have filed a bug report. Thank you for reporting this.
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