> I set up a Travelling Salesman Problem model using GLPK. When I > increase the number of cities, I run into this message:
> Warning: numerical instability (primal simplex, phase II) > * 24: obj = 3.065645000e+06 infeas = 1.747e-20 (0) > Could someone please tell me what this refers to and what I can do > about it. The warning means that due to round-off errors the current basis became primal infesible, so the simplex solver switched to phase I to restore primal feasibility and then continued the search. > For example, are there parameters I can tweak to get rid of this > message? I am aware of glp_iocp but don't understand where its > specific parameters can be used in the face of the issue above. You can enable/disable the terminal output with glp_term_out routine. > Also, after that message I get a *lot* of messages like this: > +555052: mip = not found yet >= 3.065645938e+06 (89009; > 260251) > +555716: mip = not found yet >= 3.065645938e+06 (89070; > 260620) > +556402: mip = not found yet >= 3.065645938e+06 (89158; > 260968) The glpk mip solver reports the search progress every 5 secs. > Would this be related to the first problem (about numerical > instability)? No. > It seems to get stuck at this point. Your instance/formulation is hard for the glpk mip solver due to its size and combinatorial nature. FYI: You might try to solve tsp with Concorde using glpk as an underlying lp solver. For more details see examples/cplex/README. Andrew Makhorin _______________________________________________ Help-glpk mailing list [email protected] http://lists.gnu.org/mailman/listinfo/help-glpk
