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Test Eclipse
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!
In 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
| Code Block |
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Eclipse {rarr} {rrar} 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! In 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 {code}// TODO Auto-generated method stub{code} by {code} |
by
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System.out.println("Hello World!"){code}
Save the file {{; |
Save the file TestClass.java
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by
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hitting
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Ctrl+s
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or
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the
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save
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button
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(top
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left
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on
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the
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menu
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bar).
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To
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run
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your
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code,
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go
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to
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the
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top
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center
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of
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the
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menu
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bar
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and
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hit
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the
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run
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icon
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(its
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a
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green
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circle
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with
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a
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white
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arrow
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inside),
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or
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go
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to
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the
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menu
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bar
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and
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hit
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Run → Run. The Console should pop up on the bottom with the output of your program.
Test Cplex from Eclipse
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\
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cplex.jar- Linux:
/opt/IBM/ILOG/CPLEX_Studio125/cplex/lib/cplex.jar - Mac:
/Users/<yourusername>/Applications/IBM/ILOG/CPLEX_Studio125/cplex/lib/cplex.jar
Copy the file cplex.jar and paste it in the newly created lib folder in our project. Right click on sandbox in 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 file sandbox/lib/cplex.jar
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,
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then
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hit
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OK
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until
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we
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have
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exited
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all
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the
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menus.
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Open
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up
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KnapsackSolver
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and
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replace
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the
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text
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of
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the
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file
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with
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the
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following:
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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)); } } {code} |
Run
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the
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code.
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The
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final
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line
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of
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output
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should
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of
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course
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be
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[0.0,
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1.0,
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1.0,
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0.0
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]
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,
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up
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to
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some
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precision. Upload the output of the program as your assignment here If you get the error
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.
| Warning | ||
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If your VM argument would have a space, you need to put quotes around it, as in the Windows example above. |
Finally, hit Run on the bottom.