> I'm solving a semiconductor routing problem, and running glpsol, I'm > running into very long solution times, accompanied by very small > infeasibility numbers.
> Some questions: > *) What do the infeasibility numbers mean? Does it matter that they're > very small? Once a next node subproblem is selected, the mip solver uses the dual simplex to find optimal solution to its lp relaxation. If the solution takes more than 5 seconds, the underlying simplex solver starts terminal output to prevent a "dead screen", so you see something like this: . . . +129044: mip = not found yet <= 2.400000000e+002 (14; 9) |130400: obj = 2.400000000e+002 infeas = 0.000e+000 (664) |130600: obj = 2.400000000e+002 infeas = 0.000e+000 (663) |130800: obj = 2.400000000e+002 infeas = 1.988e-014 (662) |131000: obj = 2.400000000e+002 infeas = 0.000e+000 (662) . . . 'infeas' is the sum of scaled dual infeasibilities usually reported by the glpk simplex solvers. Normally it must be close to zero, because on re-optimization the current basic solution is always dual feasible within a working precision. > *) Is there a way/runtime-option I can use to speed up the solution > times? Your instance seems to be highly degenerate and therefore hard for the glpk mip solver. You could try either reformulating it or using cutting plane options. _______________________________________________ Help-glpk mailing list [email protected] http://lists.gnu.org/mailman/listinfo/help-glpk
