[SCIP] SCIP pricer is generating the same column

[Theo Francois]

Dear SCIP Team,
I am using the python interface of SCIP pyscipopt to implement a column generation algorithm for the Resource Constrained Modulo Scheduling problem, and I have some issues regarding the process.
Since the first iteration for my instances, the columns generated are all the same. It may come from the reduced costs but those were already implemented in a column generation algorithm I coded myself and it just works fine. It looks like when I printed the details of constraints that the new columns are added correctly by the pricer to the master problem but for some reasons the dual variables remain unchanged from one iteration to the other, which lead to the generation of the same column.
I implemented my model following the cutting stock example test_pricer.py and I wasn't able to determine what was causing the dual problem to find the very same dual solutions despite the introduction of a truly improving column.
Is there any possibility to help me ?
If you want further informations on the model itself, I presented it briefly in a joint pdf. You will also find an instance and the code associated if there is a necessity to perform tests (I implemented at the end of the pricer an interruption condition to avoid the infinite loop caused by the generation of the same column).
Best regards,
Théo FRANCOIS,Research intern at LAAS-CNRS
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