> we have found an ilp formulation (file glpk.mps) on which > glpsol with default options finds a solution > (the produced output is in default.txt) and on which > advanced MIP solver doesn't find (output: intopt.txt). > Is it a bug of glpk or are we doing something wrong?
Thank you for your report. This is not a bug. The difference appears due to huge coefficients in some constraints, for example: R0001162: + C0000011 + 4294967295 C0000140 + C0000516 - C0000527 <= 4294967295 Most probably such huge coefficients introduce excessive round-off errors during the preprocessing phase. Note that the successful solution of your instance with the standard b&b was a happy chance. The "big M" method is not a good modeling technique, because it makes the problem too hard to be solved in floating-point arithmetic. Andrew Makhorin _______________________________________________ Bug-glpk mailing list [email protected] http://lists.gnu.org/mailman/listinfo/bug-glpk
