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Accessing Solution Information

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If a solution was found with the solve method, it can be accessed and then queried using a variety of methods. The objective function can be accessed by calling 

  double objval = cplex.getObjValue();

The values of individual modeling variables for the solution are accessed by calling methods IloCplex.getValue, for example: 

  double x1 = cplex.getValue(var1);

Frequently, solution values for an array of variables are needed. Rather than having to implement a loop to query the solution values variable by variable, the method IloCplex.getValues is provided to do so with only one function call: 

  double[] x = cplex.getValues(vars);

Similarly, slack values can be queried for the constraints in the active model using the methods IloCplex.getSlack or IloCplex.getSlacks.

Printing the Solution to the Diet Model

This can now be applied to solving the diet problem discussed earlier, and printing its solution. 

      IloCplex     cplex = new IloCplex();
      IloNumVar[]  Buy   = new IloNumVar[nFoods];

      if ( byColumn ) buildModelByColumn(cplex, data, Buy, varType);
      else            buildModelByRow   (cplex, data, Buy, varType);

      // Solve model
 
      if ( cplex.solve() ) { 
        System.out.println();
        System.out.println("Solution status = " + cplex.getStatus());
        System.out.println();
        System.out.println(" cost = " + cplex.getObjValue());
        for (int i = 0; i < nFoods; i++) {
          System.out.println(" Buy" + i + " = " + 
                             cplex.getValue(Buy[i]));
        }
        System.out.println();
      }

These lines of code start by creating a new IloCplex object and passing it, along with the raw data in another object, either to the method buildModelByColumn or to the method buildModelByRow. The array of variables returned by it is saved as the array Buy. Then the method solve is called to optimize the active model and, upon success, solution information is printed.

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