Originally posted by: PriteeAgrawal

Hi all,

I use OPL Java API for solving MILP problems. I am solving dantzig wolfe problem and get the below error for the master problem but could not understand what the below error means. 

java.lang.RuntimeException: internal error (Please notify IBM)

Please find attached my code for the program where the error comes for the solveMaster method.

public MasterVal solveMaster(int[] resAvail, ArrayList <RetVal> sol )throws Exception {

}

When I use cplex.jar instead of oplall.jar then I get this backtrace:

java.lang.NullPointerException
        at ilog.cplex.CpxQTermExtractor.visitMult(CpxQextractor.java:247)
        at ilog.cplex.CpxMult.accept(CpxMult.java:23)
        at ilog.cplex.CpxQextractor.visitMult(CpxQextractor.java:102)
        at ilog.cplex.CpxMult.accept(CpxMult.java:23)
        at ilog.cplex.CpxQextractor.visitLinkedExpr(CpxQextractor.java:77)
        at ilog.cplex.CpxLinkedExpr.accept(CpxLinkedExpr.java:46)
        at ilog.cplex.CpxRange.<init>(CpxRange.java:1337)
        at ilog.cplex.IloCplexModeler.addRange(IloCplexModeler.java:4327)
        at ilog.cplex.IloCplexModeler.addLe(IloCplexModeler.java:4690)
        at Main.solveMaster(Main.java:766)
        at Main.solveDW(Main.java:811)
        at Main.main(Main.java:884)

This happens because u[index] used in Main.java:765 is null. Using null arguments in IloCplex.prod() is not supported and will result in an exception or crash sooner or later. You should make sure that you don't pass null pointers here.

Originally posted by: PriteeAgrawal

Thanks  Daniel,

I got my mistake that I had not initialized my U[index]. It was so stupid of me. 

Originally posted by: PriteeAgrawal

Hi,

In my same program for Dantzig wolfe, I have binary variable delta(0,1) and hence this problem is a MIP. I am trying to fetch dual variables for my constraints in solveMaster method but i get CPLEX error 1017: Not available for mixed-integer programs.

public MasterVal solveMaster(int[] resAvail, ArrayList <TotalRetVal> sol )throws Exception {

}

I also tried cplex.solveFixed() method inside my cplex.solve() to get dual values for MIP but still it doesn't work. Please advice on how can I fetch dual values for these constraints in MIP. I am attaching the java file "Main_copy_CC_combined.java" for your reference.

Originally posted by: TobiasAchterberg

It is clear that you cannot get duals for a MIP solution, because integer programs do not have a (reasonably simple) dual.

But the solveFixed() should, after having called solve(), temporarily turn the MIP into an LP by fixing the integer variables to their solution values. Then, getDual() should work. At which point in your source code do you get the exception when you enable the solveFixed() call?

With solveFixed() enabled, do you still get error 1017 or do you get some other error?