Originally posted by: QiuFeng

Dear All:
I have a question about solution status. When I use IloCplex::getCplexStatus to inquiry the solution status, it returns "InfOrUnbd"(I saw the screen output saying "dual infeasible due to empty column ........"). But I need to know the specific solution status by calling this function: Infeasible or Unbounded, because the subsequent actions in my code depend on this information. Is there a way that I could get further information if it's infeasible or unbounded.
btw, all concert and cplex parameter are set to default.

Thanks!
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Originally posted by: SystemAdmin

Try turning off presolve and using primal simplex.
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Originally posted by: SystemAdmin

The "infeasible or unbounded" status that you get from presolve means that presolve found a way to improve the objective arbitrarily without compromising feasibility. Essentially it means that presolve has found an unbounded ray in the primal problem. But it is not clear whether there exists a primal feasible solution: it can very well be that the problem has both, primal and dual unbounded rays, which in turn means that it is both primal and dual infeasible.

If you hit such a status, you can disable presolve. Typically, this will give you then the desired answer whether the problem is infeasible or not. If all else fails, you can also set the objective function to zero, which should remove any unboundness from your problem. If you then find a feasible solution, you know that the original problem was unbounded.
Tobias
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Originally posted by: QiuFeng

Hi Denial and Tobias:
Thanks for your help. Turning off presolve did resolve my problem. Because I know my data, so I don't have to worry about primal infeasibility.
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