>> The lower bound obtained from a relaxation is only a bound. Its value >> may depend, for example, on transformations performed by presolver or >> on cutting planes added to the relaxation. So it does not express any >> essential information. > I agree with you, but when using cplex I use it as an indication of the > progress of the solver. If the lower bound only changes in, say, the 12th > digit it is quite likely that the solver will run out of memory before the > optimal solution is found. So if it would be possible to optionally print > it I would most likely use it for this kind of thing.
In most cases the lower bound does not increases smoothly; it keeps its value until corresponding node has been pruned, so it is not a good indicator of the progress. In glpk a better indication is the number of active and fathomed nodes displayed in parentheses. If the number of active nodes increases much faster than the number of fathomed nodes for a long time (say, one hour), the problem is hard for glpk solver. _______________________________________________ Help-glpk mailing list [email protected] http://lists.gnu.org/mailman/listinfo/help-glpk
