I looked around for a while, but I couldn't find a precise answer to the following question.
If I'm given a candidate solution for a (mixed) integer (convex) program, what's the complexity of deciding whether this solution (a point in the decision space) is optimal or not? I imagine that this decision problem is not NP (i.e., optimality of a MIP feasible solution can't be certified in polynomial time), right? Do you know any text or a reference where this problem is treated in detail?
Thank you very much!