[Scip] why the optimal solution has varaible with negative reduced cost

[lixiangyong at 163.com]

Dear all,


I am using SCIP with cplex to implement the branch and price for minimization problem.

I found after several columns were added at each round,  the resulting model has an optimal solution of which some variables have negative reduced cost (min problem).  

Thanks, 

Xiangyong
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