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Problem with bounds in MIP solver

Question asked by Mona Asudegi on Aug 7, 2012
Latest reply on Aug 11, 2014 by Michael.Perr



I have a minimization integer problem. Xpress solver solves it for optimal solution. However, sometimes, the solution is less than the LP relaxed solution. When checking the MIP solution graph, it shows than in the middle of the problem, the best bound suddenly drops lower than the LP relaxed bound and a solution is found in that point. I have been struggling with the issue for a couple of weeks  but couldn't find the reason. I would really appreciate any idea or comments on it.