[Coin-discuss] non-integer solution for integer linear program? what goes wrong?

[Wiebe Kirsten (Stud. FdEWB)]

Hello,
what can go wrong if I get a non-integer solution to the following integer linear program :
 
// initialize model for MPS

modelForILP = new ClpSimplex;

//set columns

modelForILP->resize(0,nrCol);

// x-variables are binary and 

// have coefficient weight[i][j] in the objective 

for (int i=0;i<nrJournals-1;i++)

{

   for (int j=i+1;j<nrJournals;j++)

   {

      counter[i][j] = counterNrCol;

      counterNrCol++;

      //putting (c[i][j]-c[j][i])*x[i][j]+ c[j][i] in the objective

      modelForILP->setObjCoeff(counter[i][j],c[i][j]-c[j][i]);

      modelForILP->setColLower(counter[i][j],0.0);

      modelForILP->setColumnUpper(counter[i][j],1.0);

      modelForILP->setInteger(counter[i][j]);

   }

}

modelForILP->setOptimizationDirection(1.0); //1.0 minimizing, -1.0 maximizing

//add constraints

// 0 <= x[i][j] + x[j][k] - x[i][k] <= 1

rowIndex = new int[3];

rowValue = new double[3];

for(int i=0;i<nrJournals-2;i++)//nrJournals-2 oder nrJournals

{

   for(int j=i+1;j<nrJournals;j++)//j=i+1 and nrJournals-1 oder 0 and nrJournals

   {

      for(int k=j+1;k<nrJournals;k++)//k=j+1 oder k=0

      {

         if(i!=j && j<k && k!=i)

         {

            rowIndex[0] = counter[i][j];

            rowIndex[1] = counter[j][k];

            rowIndex[2] = counter[i][k];

            rowValue[0] = 1;

            rowValue[1] = 1;

            rowValue[2] = -1;

            modelForILP->addRow(3,rowIndex,rowValue,0.0,1.0);

         } 

      }

   }

}

delete []rowIndex;

delete []rowValue;

 
and then depending on the situation, add the following type of contraints, where temp4 = 0 or 1
 
rowIndex = new int[1];

rowValue = new double[1];

rowIndex[0] = variable; //column-number, i.e. the variable that has to be fixed

rowValue[0] = 1;

modelForILP->addRow(1,rowIndex,rowValue,temp4,temp4);

delete []rowIndex;

delete []rowValue;

 
I'd be very happy if anyone of you has an idea!!!
kind regards
Kirsten
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