Query ruled out values for binary variables in callback
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When Gurobi knows, that there is no feasible/optimal solution with (binary variable x_3) x_3 = 1, it would be cool if this could be queried during the callback. Not that Gurobi should try to look for this specifically, if it could just tell me which variables it has already fixed during branch and bound when it returns a relaxation, that would be simple but amazing already!
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Yes, I too really need a way to determine what variables Gurobi has already fixed as part of its branching. This information should be available in the node or solution callback. Even if it was just the most-recently branched variable, that would help a lot.
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Similar to Query which binary variables have known values during optimization in order to add additional constraints, this would result in disclosing parts of Gurobi's IP. I cannot tell whether we decide to disclose branching information in the future but currently there are no plans for this.
Currently, the best you could do is to check which variables are fixed/removed by presolve by inspecting the presolved model.
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