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Open eclipse and select your workspace. If you start out with a blue screen with some circular buttons saying Welcome, Tutorial, etc., click Go to Workbench. Otherwise, you are already at the workbench. Go to File → New → Java Project. Name your project sandbox, then click the button Finish. You now have a new project!

Wiki MarkupIn the Package Explorer (left side) right click the arrow next to {{sandbox}} to expand the project. Right click on the {{src}} folder and then go to _new → class_. Name the class {{TestClass}}. Under "Which method stubs would you like to create?" check the box next to {{public static void main(String\[\] args)}}. Hit the _Finish_ button. Then replace

// TODO Auto-generated method stub

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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));
	}
}

Wiki MarkupRun the code. The final line of output should of course be {{\[0.0, 1.0, 1.0, 0.0\]}}, up to some precision. Upload the output of the program as your assignment [here|https://stellar.mit.edu/S/course/15/ia13/15.S60/homework/assignment4/] If you get the errorunmigrated-wiki-markup

{{Exception in thread "main" java.lang.UnsatisfiedLinkError: ilog.cplex.Cplex.CPXopenCPLEX(\[I)J}}

then your PATH was not set properly. The easiest way to deal with this is to add a virtual machine argument to the Run Configuration. Starting from the menu bar at the top, select Run → Run Configurations... and then on the left, make sure Java Application → KnapsackSolver is selected. In the center panel, pick the ( x )=Arguments tab. In the second box, titled VM Arguments, add the line:

• Linux: -Djava.library.path=/opt/ibm/ILOG/CPLEX_Studio125/cplex/bin/x86-64_sles10_4.1
• Windows: -Djava.library.path="C:\Program Files\IBM\ILOG\CPLEX_Studio125\cplex\bin\x64_win64"
• Mac: -Djava.library.path=/Users/<yourusername>/Applications/IBM/ILOG/CPLEX_Studio125/cplex/bin/x86-64_darwin

As you can see, the VM argument is telling java the directory that the c code of cplex is located in.

Finally, hit Run on the bottom.