Hi guys, I would like to ask you for a help with one lp problem. We are using version 4.61 with the following code:
glp_write_lp(lp, 0, "problem.lp"); glp_iocp parm; glp_init_iocp(&parm); parm.msg_lev = GLP_MSG_OFF; parm.presolve = GLP_ON; glp_intopt(lp, &parm); and glp_intopt() call runs "forever". I was reading docs and found note there: *Note that the GLPK branch-and-cut solver is not perfect, so it is unable to solve hard or very large scale MIP instances for a reasonable time.* The lp problem on which it freezes is following: \* Problem: amounts *\ Minimize obj: + 0.03 x_6 + 0.0375 x_7 + 0.1 x_8 + 0.0333333333333333 x_9 Subject To r_1: + 9.281400000008 x_5 + 2.548 x_4 + 0.17905 x_3 + 2.9625 x_2 + 1.0491 x_1 - ~r_1 = -80000 r_2: + 9.2814 x_5 + 0.744 x_4 + 0.02325 x_3 + 0.34875 x_2 + 0.0651 x_1 - ~r_2 = -32000 r_3: + 4e-12 x_5 + 0.369 x_4 + 0.10291 x_3 + 1.99875 x_2 + 0.0082 x_1 - ~r_3 = -12000 r_4: + 4e-12 x_5 + 1.435 x_4 + 0.05289 x_3 + 0.615 x_2 + 0.9758 x_1 - ~r_4 = -36000 r_5: + x_5 + 10 x_4 + x_3 + 18.75 x_2 + x_1 <= 800 r_6: + x_6 + 9.281400000008 x_5 + 2.548 x_4 + 0.17905 x_3 + 2.9625 x_2 + 1.0491 x_1 >= 400 r_7: - x_6 + 9.281400000008 x_5 + 2.548 x_4 + 0.17905 x_3 + 2.9625 x_2 + 1.0491 x_1 <= 400 r_8: + x_7 + 9.2814 x_5 + 0.744 x_4 + 0.02325 x_3 + 0.34875 x_2 + 0.0651 x_1 >= 160 r_9: - x_7 + 9.2814 x_5 + 0.744 x_4 + 0.02325 x_3 + 0.34875 x_2 + 0.0651 x_1 <= 160 r_10: + x_8 + 4e-12 x_5 + 0.369 x_4 + 0.10291 x_3 + 1.99875 x_2 + 0.0082 x_1 >= 60 r_11: - x_8 + 4e-12 x_5 + 0.369 x_4 + 0.10291 x_3 + 1.99875 x_2 + 0.0082 x_1 <= 60 r_12: + x_9 + 4e-12 x_5 + 1.435 x_4 + 0.05289 x_3 + 0.615 x_2 + 0.9758 x_1 >= 180 r_13: - x_9 + 4e-12 x_5 + 1.435 x_4 + 0.05289 x_3 + 0.615 x_2 + 0.9758 x_1 <= 180 Bounds 0 <= ~r_1 <= 160000 0 <= ~r_2 <= 64000 0 <= ~r_3 <= 24000 0 <= ~r_4 <= 72000 100 <= x_1 <= 400 8 <= x_2 <= 16 2 <= x_3 <= 400 4 <= x_4 <= 20 4 <= x_5 <= 30 Generals x_1 x_2 x_3 x_4 x_5 End It does not seems to be large scale, and I am not sure if this is classified as hard problem? Also the interesting part is that on the older version of glpk it was solved without any problems. Thanks for help. -- S pozdravom Dušan Plavák
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