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Open Eclipse and expand the sandbox project we created previously. Create a new class called KnapsackSolver. Next we are going to connect to Cplex. Right click on sandbox in the package explorer and select new->folder. Give it the name lib and click "Finish." Find the file cplex.jar in your Cplex installation. On my Windows installation, it was located at
- Windows:
C:\Program Files\IBM\ILOG\CPLEX_Studio125\cplex\lib\cplex.jar - Linux:
/opt/IBM/ILOG/CPLEX_Studio125/cplex/lib/cplex.jarTODO check - Mac: Unknown.
Copy the file cplex.jar and paste it in the newly createdlibfolder in our project. Right click onsandboxin the package explorer, then select Build Path → Configure Build Path... Select the Libraries tab, then hit the Add JARs button (see here for an explanation of what all these buttons do). Select the filesandbox/lib/cplex.jar, then hit OK until we have exited all the menus.
Open up KnapsackSolver and replace the text of the file with the following:
| Code Block | ||
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import java.util.Arrays;
import ilog.concert.IloException;
import ilog.concert.IloIntVar;
import ilog.cplex.IloCplex;
public class KnapsackSolver {
public static double[] solveKnapsack(double[] values, double[] weights, double capacity){
if(weights.length != values.length){
throw new RuntimeException("values.length was " + values.length
+ " and weights.length was" + weights.length
+ " but they must be the same");
}
try {
IloCplex cplex = new IloCplex();
IloIntVar[] x = cplex.boolVarArray(values.length);
cplex.addLe(cplex.scalProd(x, weights), capacity);
cplex.addMaximize(cplex.scalProd(x, values));
cplex.solve();
return cplex.getValues(x);
} catch (IloException e) {
throw new RuntimeException();
}
}
public static void main(String[] args){
double[] values = new double[]{2,4,5,6};
double[] weights= new double[]{2,3,4,7};
double capacity = 8;
double[] solution = solveKnapsack(values,weights,capacity);
System.out.println(Arrays.toString(solution));
}
}
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