Bitwise operator Python vs Julia

Answered

Wiktor Wisniewski

• September 14, 2022 06:31
• Edited

I have a working model in python.

mdl = Model('myModel')
mdl.setParam('MIPGap', 0.000001)
mdl.setParam('TimeLimit', 10)

x = mdl.addVars(A, vtype=GRB.BINARY)
u = mdl.addVars(N, vtype=GRB.CONTINUOUS)

mdl.modelSense = GRB.MINIMIZE;
mdl.setObjective(quicksum(x[i,j]*c[i,j] for i,j in A))

mdl.addConstrs(quicksum(x[i,j] for j in V if j!=i)==1 for i in N);
mdl.addConstrs(quicksum(x[i,j] for i in V if i!=j)==1 for j in N);
mdl.addConstrs((x[i,j]==1) >> (u[i]+q[j]==u[j]) for i,j in A if i!= 0 and j!=0);
mdl.addConstrs(u[i]>=q[i] for i in N);
mdl.addConstrs(u[i]<=Q for i in N);

What I am doing is rewriting it in Julia using Jump, but I don't know how to add constraint "(x[i,j]==1) >> (u[i]+q[j]==u[j]) for i,j in A if i!= 0 and j!=0". I tried something like this:

"@constraint(mdl, x[i,j] >> u[i]+d[j]==u[j] for (i,j) in A if i!= 0 & j!=0);"

but it is not working. How should I do it?

1

• 

  Jaromił Najman

  Gurobi Staff

  • September 14, 2022 07:40
  • Edited

  This is more of a Julia Jump related question, so it might be better to ask in a Julia/JuMP forum.

  Nevertheless, you want to formulate constraints of the form "if \(x=1\) then \(u+q=w\)". I don't know whether JuMP supports indicator constraints but you can formulate an indicator constraint "by hand" as described in How do I model conditional statements in Gurobi? I assume that your \(x\) is binary, so you could formulate the conditional statement "if \(x \geq 0.5\) then \(u+q=w\)".

  Moreover, the thread Conditional constraint if else in JuMP might be helpful .

  Best regards, 
  Jaromił

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• 

  Wiktor Wisniewski

  • September 14, 2022 18:03

  

  

  

  Jaromił Najman thank you for your answer, but ConditionalJump does not support newer version of JuMP, which I need. How exactly that code "by hand" would look like in this case?

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• 

  Jaromił Najman

  Gurobi Staff

  • September 15, 2022 07:17

  How exactly that code "by hand" would look like in this case?

  The Knowledge Base article How do I model conditional statements in Gurobi? describes a formulation which you would have to implement in JuMP. In the formulation described in the article, if your \(x\) variable is binary, you can set \(y=0.5\) and set \(\epsilon=0\).

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