Gurobi in Java - How can I add two Expression?

Ongoing

Fulya Terzi

• June 22, 2020 08:26

Hello,

I declare a new expression such as GRBQuadExpr[ ] ObjExpr = new GRBQuadExpr[size]; 

I have another two expressions such as GRBLinExpr LinObjExpr and GRBQuadExpr QuadObjExpr. 

for ( count=0; count<size; count++){

   ObjExpr[count] = LinObjExpr + QuadObjExpr

}

This summation is wrong. In Cplex there is a built-in function, model.sum, to add expressions. Is there any built-in function in Gurobi?

 

Thank you in advance.

0

• 

  Jaromił Najman

  Gurobi Staff

  • July 28, 2020 10:03

  Hi,

  you could use the add() function as

  ObjExpr[count].add(LinObjExpr);
  ObjExpr[count].add(QuadObjExpr);

  Does this work for you?

  Best regards,
  Jaromił

  0
• 

  Fulya Terzi

  • September 22, 2020 11:56

  

  

  Hi Jaromil,

  How do you define ObjExpr in this code? I wrote the code and defined ObjExpr as GRBQuadExpr[ ] but gives error?

   

  Thank you in advance

  Best regards,

   

  Fulya

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• 

  Jaromił Najman

  Gurobi Staff

  • September 22, 2020 12:13
  • Edited

  Dear Fulya,

  What kind of error do you get?

  Here is an example code:

  GRBLinExpr l1 = new GRBLinExpr();
  l1.addTerm(1.0, x); // adding 1.0 * x to l1 where x is a GRBVar
  
  GRBQuadExpr q1 = new GRBQuadExpr();
  q1.addTerm(1.0, x, y); // adding 1.0 * x * y to q1 where x and y are GRBVar
  
  GRBQuadExpr obj = new GRBQuadExpr();
  obj.add(l1); // adding GRBLinExpr to obj
  obj.add(q1); // adding GRBQuadExpr to obj

  Does this help?

  Best regards,
  Jaromił

  0
• 

  Fulya Terzi

  • September 25, 2020 11:26

  

  

  Dear Jaromil,

  The error is NullPointerException. The error line is shown in 

  GRBQuadExpr[] objExpr = new GRBQuadExpr[sizeOfTerm];
  
  GRBQuadExpr Sum = new GRBQuadExpr(); // yeni Ekledim
  GRBLinExpr linearCoeff = new GRBLinExpr();
  GRBQuadExpr quadCoeff = new GRBQuadExpr();
  
  for (Entry<Integer, Map<String, HourlySegmentNewGurobi>> entry : hourlySegments.entrySet()) {
       period = entry.getKey();
  
       for (String segmentId : hourlySegments.get(period).keySet()) {
  
           linearCoeff = setLinearCoeffOfHourly(hourlySegments.get(period).get(segmentId),
                         model, hourlyVars.get(segmentId));
  
           quadCoeff = setQuadraticCoeffOfHourly(hourlySegments.get(period).get(segmentId), model,
                       hourlyVars.get(segmentId));
  
           objExpr[count].add(linearCoeff); // This line 
           objExpr[count].add(quadCoeff);
  
           Sum.add(coeffsOfHourly[count]);
           count++;
      }
  }

   

  Best Regards,

  Thank you

  0
• 

  Jaromił Najman

  Gurobi Staff

  • September 25, 2020 12:09
  • Edited

  Dear Fulya,

  It seems like the \(\texttt{linearCoeff}\) object you calculate via your \(\texttt{setLinearCoeffOfHourly}\) function is a \(\texttt{NullPointer}\). You could check this by

  if (linearCoeff == null){
      System.out.println("Error: linearCoeff is a NullPointer");
  }

  Best regards,
  Jaromił

  0
• 

  Fulya Terzi

  • September 25, 2020 12:42

  

  

  Dear Jaromil,

  I wrote after this code

  linearCoeff = setLinearCoeffOfHourly(hourlySegments.get(period).get(segmentId),
                         model, hourlyVars.get(segmentId));

  and checked it but the code do not give this error message.

  Best Regards,

  Fulya

   

  0
• 

  Jaromił Najman

  Gurobi Staff

  • September 25, 2020 16:49

  Dear Fulya,

  Could you post the whole \(\texttt{NullPointerException}\) error message you are getting?

  Best regards,
  Jaromił

  0
• 

  Fulya Terzi

  • September 28, 2020 07:09

  

  

  Dear Jaromil,

  The error message such that

  Exception in thread "main" java.lang.NullPointerException

  After that shows the places:

  at ....ObjectiveFunctionNewGurobi.setExprForHourly(ObjectiveFunctionNewGurobi.java:117)
  at ....ObjectiveFunctionNewGurobi.setQuadratic(ObjectiveFunctionNewGurobi.java:42)
  at ....SolverNewGurobi.setupModel(SolverNewGurobi.java:363)
  at ....SolverNewGurobi.<init>(SolverNewGurobi.java:76)
  at ....OptimizationEngineNewGurobi.solvePreProblem(OptimizationEngineNewGurobi.java:191)
  at ....OptimizationEngineNewGurobi.run(OptimizationEngineNewGurobi.java:131)
  at ....Main.runThroughFile(Main.java:265)
  at ....Main.main(Main.java:95)

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• 

  Jaromił Najman

  Gurobi Staff

  • September 28, 2020 08:09

  Dear Fulya,

  The error message indicates that the error comes from the \(\texttt{setExprForHourly}\) function found in file \(\texttt{ObjectiveFuncitonNewGurobi.java}\) at line 117. Please try to fix the code therein to avoid the NullPointerException.

  Best regards,
  Jaromił

  0

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