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Interactions between partition heuristic and presolve

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2 comments

  • Jaromił Najman
    Gurobi Staff Gurobi Staff

    Hi Thomas,

    Please excuse getting to you only now.

    Which partition attribute is retained in the model?

    Gurobi keeps the partition attribute value of the variable surviving the presolve process. If the presolve process leads to x1 & x2 being both eliminated or replaced by a new variable all together, then the partition attribute is reset to its default value for the newly introduced presolve variable.

    Best regards, 
    Jaromił

     

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  • Thomas Leveringhaus
    Collaborator
    Investigator
    Gurobi-versary

    Hi Jaromił Najman,

    thank you very much for your answer, which is still helpfull for me.

    As far as I know, there is no way to control which variables survive the presolve process, so I can't predifine the behaviour of the partition heuristic in such special cases we discussed here.

    I can think of arguments that speak for keeping the partition attribute of the surviving variables equal to -1, 0 or one of the sub-MIP-values, if equal variables have those different partition attributes.
    I suspect presolve is so sophisticated that it would be too complicated to define general decision rules for these special cases or to allow the user additional configuration options.

    But now I have clarity and must take care to foresee such cases as far as possible and to assign the partition attributes in advance in a meaningful way.

    Thanks

    Thomas

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