For some difficult large models, the Polishing facility in Cplex can sometimes do extremely well. This is an example:
Elapsed real time = 874.90 sec. (tree size = 11.31 MB, solutions = 2)
Starting condition for polishing reached (PolishAfterTime).
* 390+ 390 360.3876 -159.3086 285698 144.20%
GUB cover cuts applied: 854
Root node processing (before b&c):
Although the relative gap looks bad, this is in fact a very good solution. The reason for the gap problem is that we are relatively close to zero in our objective (compared to solutions found by heuristics) and the fact that we are crossing zero in the gap calculation does not help.