> tho following error occured wile version 4.26 on attached ILP problem.
> Any advice how to avoid such problems is welcome. > GLPK internal error: x <= ub; file ..\src\glpios03.c, line 265 Thank you for the bug report. This error appears, because the glpk mip solver is not sufficiently robust. As a rule the error is caused by ill-conditioned basis matrix that, in turn, leads to excessive round-off errors in solution of current lp relaxation. Probably you instance has large (in magnitude) constraint coefficients at integer variables. Please see: http://lists.gnu.org/archive/html/bug-glpk/2007-12/msg00005.html Nevertheless, I managed to solve your instance to optimality with glpsol --noscale --cuts: +590928: mip = 1.738300000e+04 >= 1.544270065e+04 11.2% (3019; 27700) +592476: mip = 1.738300000e+04 >= 1.554327064e+04 10.6% (2851; 28427) +593947: mip = 1.738300000e+04 >= 1.560953674e+04 10.2% (2608; 29436) +595559: mip = 1.738300000e+04 >= 1.580084072e+04 9.1% (2352; 30322) +596987: mip = 1.738300000e+04 >= 1.592364844e+04 8.4% (2128; 31041) +598429: mip = 1.738300000e+04 >= 1.611015105e+04 7.3% (1880; 31985) +600160: mip = 1.738300000e+04 >= 1.618175000e+04 6.9% (1627; 32967) +601728: mip = 1.738300000e+04 >= 1.633417578e+04 6.0% (1364; 33864) +603034: mip = 1.738300000e+04 >= 1.653693735e+04 4.9% (1069; 35097) +604279: mip = 1.738300000e+04 >= 1.680371170e+04 3.3% (722; 36692) +605552: mip = 1.738300000e+04 >= 1.700495011e+04 2.2% (460; 38099) +606579: mip = 1.738300000e+04 >= 1.730659137e+04 0.4% (63; 40855) +606712: mip = 1.738300000e+04 >= tree is empty 0.0% (0; 41563) INTEGER OPTIMAL SOLUTION FOUND Time used: 857.1 secs Memory used: 30.4 Mb (31907668 bytes) Result of optimisation Objective criterion: 17383 Start times s: 1080 628 1080 360 1080 1080 1080 695 648 360 960 793 960 960 960 960 780 960 780 780 840 998 840 840 840 1080 840 840 840 840 480 480 480 480 480 480 480 480 660 480 840 840 1080 1080 840 840 840 840 1080 840 660 660 660 660 660 660 660 660 660 920 1080 1080 1080 360 1080 1080 1080 1000 687 1495 Variable x: 0 0 0 0 0 0 1 0 0 0 0 0 0 0 . . . 0 0 0 0 0 0 1 0 0 0 0 0 0 0 Used vehicles: 4 Model has been successfully processed Interesting to note that the mip solver found optimial solution at once, and the rest time was spent to prove its optimality. Andrew Makhorin _______________________________________________ Bug-glpk mailing list [email protected] http://lists.gnu.org/mailman/listinfo/bug-glpk
