Error when using mycallback function with a new model

Answered

Libia Romero Escobedo

January 06, 2023 22:02 Edited

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Hello community,

I want to find a feasible solution to my model when one of the two conditions of the "mycallback" function is satisfied. callback.py - Gurobi Optimization

1) The optimality gap is less than 10%

2) At least 10000 nodes have been explored, and an integer feasible solution has been found.

Unlike the code in the online example, I am not reading my model from a file, but instead I am implementing my model by declaring the variables, constraints, the objective function. 

When I run the code I get an error here:

IndexError Traceback (most recent call last)
File src\gurobipy\callback.pxi:209, in gurobipy.CallbackClass.callback()

Cell In [1], line 63, in mycallback(model, where)
     61 if model.cbGet(GRB.Callback.MIPNODE_STATUS) == GRB.OPTIMAL:
     62 x = model.cbGetNodeRel(model._vars)
---> 63 model.cbSetSolution(model.getVars(), x)
     64 elif where == GRB.Callback.BARRIER:
     65 # Barrier callback         
     66 itcnt = model.cbGet(GRB.Callback.BARRIER_ITRCNT)

File src\gurobipy\model.pxi:6566, in gurobipy.Model.cbSetSolution() IndexError: list index out of range

Please could someone explain me how to fix this error. 

Related to

• Callbacks

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  Jaromił Najman

  • Gurobi Staff

  January 09, 2023 12:44 Edited

  Hi Libia,

  Could you provide a minimal reproducible example?

  Depending on what you are trying to achieve, it is possible that the number of variables changed in between calls such that the \(\texttt{model._vars}\) object does not longer fit the \(\texttt{model.getVars}\) call. You might want to try

  x = model.cbGetNodeRel(model._vars)
  model.cbSetSolution(model._vars, x)

  However, without an example of your executed code, it is hard to help here.

  Please note that only specific callback functions are meant to be safely callable from within a callback. Thus, using \(\texttt{model.getVars()}\) in this case is not good. We are aware that this is part of our callback.py example and will be adjusted in an upcoming release.

  Best regards, 
  Jaromił

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  Libia Romero Escobedo

  January 10, 2023 19:12

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  Thanks Jaromil, I will try your advice.

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