How to multiply two binary gurobi variables using Java?

Answered

Hadi Askaripoor

• February 16, 2022 16:53

Hello, 

I am wondering how I can multiply two gurobi variables in Java! For example, in the following code, I am going to multiply m1, as gurobi binary variable to each gurobi continuous variable in expr10. I would appreciate your guidance!

Best regards,

Hadi

GRBLinExpr expr10 = new GRBLinExpr();
GRBLinExpr expr11 = new GRBLinExpr();
((Process) next).setStart_time(this.model.addVar(0.0, 1000, 0, GRB.CONTINUOUS, "StartingTime"+ ((Process) next).getName()));
GRBVar m1 = model.addVar( 0.0, 1.0, 0.0, GRB.BINARY, "M");
expr10.addTerm(1, listofPairedProcesses.get(0).getStart_time() ); 
expr10.addTerm(-1, listofPairedProcesses.get(1).getStart_time());

0

• 

  Maliheh Aramon

  Gurobi Staff

  • February 17, 2022 05:52

  Hi Hadi, 

   

  You can define a Gurobi quadratic expression object (GRBQuadExpr) and iterate through the terms in the GRBLinExpr object already defined and multiply each term by the binary variable \(\texttt{m1}\). Please see the snippet below as an example:

   

  GRBQuadExpr quad_expr = new GRBQuadExpr();
  for (int i=0; i < expr10.size(); ++i) {
    double coeff = expr10.getCoeff(i);
    GRBVar var_1 = expr10.getVar(i);
    quad_expr.addTerm(coeff, var_1, m1);
  }

   

  Best regards,

  Maliheh

  1
• 

  Hadi Askaripoor

  • February 21, 2022 12:33

  

  

  

  Dear Maliheh,

  Thanks for your reply! If I want to multiply two gurobi  binary variables e.g. k = m1*m2 and then multiply k to the expr10, how can I proceed? I've tried the same method as you explained but it didn't work!  

  I would appreciate your help!

  0
• 

  Maliheh Aramon

  Gurobi Staff

  • February 23, 2022 05:54
  • Edited

  Hi Hadi, 

  Sorry for the delay in getting back to you. 

  It should work. I tested the snippet below and it works. Could you please try modifying your code based on the example below and re-run it again?

  GRBVar m1 = model.addVar(0.0, 1.0, 0.0, GRB.BINARY, "m1");
  GRBVar m2 = model.addVar(0.0, 1.0, 0.0, GRB.BINARY, "m2");
  GRBVar k = model.addVar(0.0, 1.0, 0.0, GRB.BINARY, "k");
  // Model k = m1 * m2
  GRBQuadExpr quad_expr_k = new GRBQuadExpr();
  quad_expr_k.addTerm(1, m1, m2);
  model.addQConstr(quad_expr_k, GRB.EQUAL, k, "c1");
  
  // Multiply k by the linear expression
  GRBQuadExpr quad_expr = new GRBQuadExpr();
  for (int i=0; i < expr10.size(); ++i) {
    double coeff = expr10.getCoeff(i);
    GRBVar var_1 = expr10.getVar(i);
    quad_expr.addTerm(coeff, var_1, k);
  }

  Best regards, 

  Maliheh

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• 

  Hadi Askaripoor

  • February 25, 2022 14:27

  

  

  

  Dear Maliheh,

  It worked, I would really appreciate your help!

  Best regards,

  Hadi

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