Interpretation of GAP in CPLEX

Question

This is a part of the engine-log output that I get from a small-scale mixed integer linear optimization problem that I solved in CPLEX 12.7.0

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Answer 1

Yes you are right. The optimality is proven if the upper bound and the lower bound evaluate the same value, i.e. CPLEX could prove an optimality gap of 0%.

Since CPLEX stops with a solution that has a gap of 0.57%, I would assume that you configured an MIP-gap <1%. If you are interested in a solution with proven optimal, you should change the MIPGap parameter to zero. See also here.