Originally posted by: K__U

Hi,

I have MILP problem with one binary and three continuous decision variable. 

With another subproblem I am generating a solution to my binary decision variable and adding it to the model with below codes:

for (var i in thisOplModel.SetCoverFinalSolution){
            opl5.Z[i.tup7][i.tup6][i.tup8].LB=1;  //Open period from set cover force main problem to LB >> 1
            }
   
for (var x=1;x<=9;x++){
      for (var j in opl5.DC){
           for    (var p in opl5.Period){
                    if(opl5.Z[x][j][p].LB!=1){opl5.Z[x][j][p].UB=0}
            }    
      }
}     

Without these UB and LB declarations model runs properly,

but with these bounds, I couldn't get an objective value and model stops running. What might be the reason ?

 

        cplex5.solve()
        writeln(opl5.printConflict()); 
        writeln("cplex5.status",cplex5.status);
        writeln("ObjFunct FullModel:",cplex5.getObjValue());    >>>>>>>> This is the line with problem 

 

Engine Log:

I checked the status of the model with below comment:

CPXPARAM_Advance                                   2
CPXPARAM_TimeLimit                                 12000
CPXPARAM_WorkMem                                20000
CPXPARAM_MIP_Tolerances_MIPGap       0.01
CPXPARAM_MIP_Strategy_File                   3
CPXPARAM_MIP_Limits_TreeMemory        10000
Tried aggregator 1 time.
MIP Presolve eliminated 587922 rows and 541196 columns.
Reduced MIP has 2078 rows, 6504 columns, and 14710 nonzeros.
Reduced MIP has 0 binaries, 0 generals, 0 SOSs, and 0 indicators.
Presolve time = 8.72 sec. (2224.89 ticks)
Tried aggregator 1 time.
Reduced MIP has 2078 rows, 6504 columns, and 14710 nonzeros.
Reduced MIP has 0 binaries, 0 generals, 0 SOSs, and 0 indicators.
Presolve time = 0.03 sec. (7.53 ticks)
MIP emphasis: balance optimality and feasibility.
MIP search method: dynamic search.
Parallel mode: deterministic, using up to 6 threads.
Root relaxation solution time = 0.05 sec. (34.67 ticks)

        Nodes                                         Cuts/
   Node  Left     Objective  IInf  Best Integer    Best Bound    ItCnt     Gap

*     0     0      integral     0   2.74910e+08   2.74910e+08     2334    0.00%
Elapsed time = 9.16 sec. (2396.93 ticks, tree = 0.00 MB, solutions = 1)

Root node processing (before b&c):
  Real time             =    9.27 sec. (2414.42 ticks)
Parallel b&c, 6 threads:
  Real time             =    0.00 sec. (0.00 ticks)
  Sync time (average)   =    0.00 sec.
  Wait time (average)   =    0.00 sec.
                          ------------
Total (root+branch&cut) =    9.27 sec. (2414.42 ticks)

 

Scripting Log:

  No conflicts available.

cplex5.status1
// Script execution failed with status -2.

 

Problems:

Description    Resource    Path    Location    Type
Exception from IBM ILOG CPLEX: CPLEX Error  1217: No solution exists.  
 

 

#DecisionOptimization
#OPLusingCPLEXOptimizer

Hi,

Without your entire model I cannot be sure but I think that

if(opl5.Z[x][j][p].LB!=1){opl5.Z[x][j][p].UB=0}

is in a loop so by changing the UB you could make the model infeasible and then when you ask for the LB next iteration you get into the error you got.

A workaround for that is to store all LB you need in a temporary array and then do a loop to change all UB you need

regards

https://www.linkedin.com/pulse/low-barrier-entry-optimization-through-cplex-alex-fleischer/

#DecisionOptimization
#OPLusingCPLEXOptimizer

Originally posted by: K__U

Hi Alex,

 

I commented the conflict printer line, and now the model is working without errors.

//        writeln(opl5.printConflict()); 

What might be the reason? 

It is not critical at the moment, but I appreciate your answer to avoid similar problems in future coding.

 

Thanks

#DecisionOptimization
#OPLusingCPLEXOptimizer