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mathematical-optimizationmodelinglinear-programminggurobi

Gurobi fails to reach optimum solution for a larger case of the same MILP formulation


My MILP problem is based on simple but large number of constraints and variables.

  1. Most of the decision variables are of 'semi' type (example production quantity , transportation quantity etc)
  2. S(wijk) is of integer type ( number of shifts on a line)
  3. Data : delta , theta , alpha , lambda , N(ijw), Mmin(ijk), Mmax(ijk), V0(ik), Dwijk  The formulation is as follows

The problem formulation reaches an optimum solution for a small scale but for larger scales it just 'stalls' at certain 'gap' and doesn't move forward

a. small scale problem size : less than 15 weeks (planning horizon)
b. larger scale problems' size : >= 15 weeks

problem input method : .lp file ( hence solved using lp.py script on command prompt)
gurobi version : 6.0 ( academic license)

Any suggestions on what I can do to obtain optimum solutions for the larger cases ?
following is an example output log for a case of 15 weeks and 124 products .

C:\gurobi600\win64\python27\bin>gurobi lp.py model124
Optimize a model with 40146 rows, 61820 columns and 160660 nonzeros
Coefficient statistics:
  Matrix range    [1e+00, 1e+04]
  Objective range [3e-01, 3e+01]
  Bounds range    [0e+00, 0e+00]
  RHS range       [8e+00, 5e+04]
Presolve removed 25296 rows and 23436 columns
Presolve time: 0.15s
Presolved: 14850 rows, 38384 columns, 87748 nonzeros
Variable types: 34754 continuous, 3630 integer (0 binary)

Root relaxation: objective 4.221641e+08, 20576 iterations, 0.27 seconds

    Nodes    |    Current Node    |     Objective Bounds      |     Work
 Expl Unexpl |  Obj  Depth IntInf | Incumbent    BestBd   Gap | It/Node Time

     0     0 4.2216e+08    0 1394          - 4.2216e+08      -     -    0s
H    0     0                    4.344708e+08 4.2216e+08  2.83%     -    1s
H    0     0                    4.269043e+08 4.2216e+08  1.11%     -    1s
     0     0 4.2246e+08    0 1296 4.2690e+08 4.2246e+08  1.04%     -    1s
     0     0 4.2255e+08    0 1199 4.2690e+08 4.2255e+08  1.02%     -    1s
     0     0 4.2260e+08    0 1141 4.2690e+08 4.2260e+08  1.01%     -    1s
     0     0 4.2260e+08    0 1140 4.2690e+08 4.2260e+08  1.01%     -    1s
     0     0 4.2260e+08    0 1139 4.2690e+08 4.2260e+08  1.01%     -    1s
     0     0 4.2260e+08    0 1135 4.2690e+08 4.2260e+08  1.01%     -    2s
     0     0 4.2260e+08    0 1395 4.2690e+08 4.2260e+08  1.01%     -    2s
H    0     0                    4.267905e+08 4.2260e+08  0.98%     -    3s
     0     0 4.2260e+08    0 1147 4.2679e+08 4.2260e+08  0.98%     -    3s
H    0     0                    4.261854e+08 4.2260e+08  0.84%     -    3s
     0     0 4.2263e+08    0 1117 4.2619e+08 4.2263e+08  0.84%     -    3s
     0     0 4.2263e+08    0 1116 4.2619e+08 4.2263e+08  0.84%     -    3s
     0     0 4.2263e+08    0 1116 4.2619e+08 4.2263e+08  0.84%     -    3s
     0     0 4.2263e+08    0 1114 4.2619e+08 4.2263e+08  0.84%     -    3s
     0     2 4.2263e+08    0 1114 4.2619e+08 4.2263e+08  0.84%     -    4s
    18    17 4.2263e+08    9 1105 4.2619e+08 4.2263e+08  0.84%  21.8    5s
H   27    27                    4.261065e+08 4.2263e+08  0.82%  16.3    5s
H   56    57                    4.260888e+08 4.2263e+08  0.81%  11.7    5s
H   57    59                    4.260728e+08 4.2263e+08  0.81%  11.6    5s
H  176   176                    4.257390e+08 4.2263e+08  0.73%  10.1    6s
H  363   366                    4.257251e+08 4.2263e+08  0.73%   9.9    9s
   451   450 4.2271e+08  153 1009 4.2573e+08 4.2263e+08  0.73%   9.6   10s
H  474   476                    4.254454e+08 4.2263e+08  0.66%   9.4   10s
H  815   816                    4.253518e+08 4.2263e+08  0.64%   9.5   13s
   984   985 4.2281e+08  336  880 4.2535e+08 4.2263e+08  0.64%   9.5   15s
H 1000   999                    4.253516e+08 4.2263e+08  0.64%   9.4   15s
H 1086  1085                    4.253373e+08 4.2263e+08  0.64%   9.4   16s
H 1482  1473                    4.253030e+08 4.2263e+08  0.63%   9.2   19s
  1505  1505 4.2297e+08  536  730 4.2530e+08 4.2263e+08  0.63%   9.1   20s
H 1552  1546                    4.252662e+08 4.2263e+08  0.62%   9.0   20s
H 1577  1580                    4.252426e+08 4.2263e+08  0.62%   9.0   21s
H 1622  1610                    4.252100e+08 4.2263e+08  0.61%   8.9   21s
H 1746  1743                    4.251278e+08 4.2263e+08  0.59%   8.7   22s
H 1779  1782                    4.250611e+08 4.2263e+08  0.57%   8.6   23s
H 1828  1820                    4.250061e+08 4.2263e+08  0.56%   8.5   23s
H 1878  1868                    4.250016e+08 4.2263e+08  0.56%   8.4   23s
H 1931  1917                    4.249827e+08 4.2263e+08  0.55%   8.3   24s
H 1978  1954                    4.248879e+08 4.2263e+08  0.53%   8.3   24s
H 2003  2003                    4.247702e+08 4.2263e+08  0.50%   8.2   39s
H 2004  2003                    4.243849e+08 4.2263e+08  0.41%   8.2   39s
  2007  2008 4.2331e+08  713  604 4.2438e+08 4.2263e+08  0.41%   8.2   40s
H 2450  2450                    4.242743e+08 4.2263e+08  0.39%   7.4   45s
H 2505  2478                    4.242170e+08 4.2263e+08  0.38%   7.3   47s
  2614  2614 4.2371e+08  921  450 4.2422e+08 4.2263e+08  0.38%   7.1   50s
H 2898  2900                    4.242040e+08 4.2263e+08  0.37%   6.9   54s
  2899  2897 4.2385e+08 1011  397 4.2420e+08 4.2263e+08  0.37%   6.9   55s
  3652  3643 4.2416e+08 1247  242 4.2420e+08 4.2263e+08  0.37%   6.5   60s
  3980  3911 4.2265e+08   12 1080 4.2420e+08 4.2265e+08  0.37%  11.6   65s
  4402  4192 4.2298e+08  119 1002 4.2420e+08 4.2265e+08  0.37%  11.3   71s
  4739  4415 4.2313e+08  206  936 4.2420e+08 4.2265e+08  0.37%  11.2   75s
  5194  4723 4.2327e+08  327  863 4.2420e+08 4.2265e+08  0.37%  11.0   81s
  5600  4990 4.2335e+08  430  800 4.2420e+08 4.2265e+08  0.37%  10.9   85s
  6055  5294 4.2347e+08  544  722 4.2420e+08 4.2265e+08  0.37%  10.7   91s
  6526  5610 4.2357e+08  662  647 4.2420e+08 4.2265e+08  0.37%  10.6   96s
  6840  5818 4.2364e+08  743  579 4.2420e+08 4.2265e+08  0.37%  10.5  100s
  7381  6177 4.2376e+08  880  481 4.2420e+08 4.2265e+08  0.37%  10.4  106s
  7745  6422 4.2383e+08  970  414 4.2420e+08 4.2265e+08  0.37%  10.3  110s
  7955  6560 4.2386e+08 1024  370 4.2420e+08 4.2265e+08  0.37%  10.3  119s
  8079  6642 4.2388e+08 1055  342 4.2420e+08 4.2265e+08  0.37%  10.3  121s
  8574  6974 4.2399e+08 1180  242 4.2420e+08 4.2265e+08  0.37%  10.1  126s
  9087  7317 4.2413e+08 1313  174 4.2420e+08 4.2265e+08  0.37%   9.9  131s
H 9675  6763                    4.240515e+08 4.2265e+08  0.33%   9.7  139s
  9677  6760     cutoff 1472      4.2405e+08 4.2265e+08  0.33%   9.7  142s
H 9913  6697                    4.240485e+08 4.2266e+08  0.33%   9.7  148s
H 9914  6503                    4.240433e+08 4.2266e+08  0.33%   9.7  148s
  9915  6510 4.2282e+08   70 1044 4.2404e+08 4.2266e+08  0.33%   9.7  151s
 10194  6691 4.2295e+08  137 1002 4.2404e+08 4.2266e+08  0.33%   9.6  157s
 10196  6695 4.2295e+08  137 1003 4.2404e+08 4.2266e+08  0.33%   9.6  160s
 10843  7125 4.2327e+08  297  881 4.2404e+08 4.2266e+08  0.33%   9.6  167s
 11170  7343 4.2335e+08  376  835 4.2404e+08 4.2266e+08  0.33%   9.5  171s
H11485  7331                    4.240303e+08 4.2266e+08  0.32%   9.5  176s
 11651  7447 4.2345e+08  455  798 4.2403e+08 4.2266e+08  0.32%   9.5  180s
 12009  7680 4.2356e+08  548  735 4.2403e+08 4.2266e+08  0.32%   9.4  186s
H12010  7497                    4.240210e+08 4.2266e+08  0.32%   9.4  186s
 12011  7500 4.2356e+08  548  734 4.2402e+08 4.2266e+08  0.32%   9.4  190s
 12748  7991 4.2376e+08  737  605 4.2402e+08 4.2266e+08  0.32%   9.3  198s
 13135  8275 4.2382e+08  831  528 4.2402e+08 4.2266e+08  0.32%   9.3  203s
 13534  8670 4.2389e+08  928  450 4.2402e+08 4.2266e+08  0.32%   9.2  207s
 13912  9012 4.2395e+08 1024  404 4.2402e+08 4.2266e+08  0.32%   9.2  212s
H14310  9370                    4.240165e+08 4.2266e+08  0.32%   9.2  218s
 14323  9388 4.2401e+08 1125  319 4.2402e+08 4.2266e+08  0.32%   9.2  220s
 14858  9900 4.2290e+08  124 1006 4.2402e+08 4.2266e+08  0.32%   9.2  251s
 14900  9944 4.2291e+08  129  999 4.2402e+08 4.2266e+08  0.32%   9.2  256s
 15362 10409 4.2306e+08  201  942 4.2402e+08 4.2266e+08  0.32%   9.2  261s
 15822 10886 4.2317e+08  283  883 4.2402e+08 4.2266e+08  0.32%   9.1  265s
 16264 11314 4.2327e+08  339  857 4.2402e+08 4.2266e+08  0.32%   9.1  270s
 16698 11771 4.2333e+08  400  822 4.2402e+08 4.2266e+08  0.32%   9.1  275s
 17470 12516 4.2352e+08  493 1135 4.2402e+08 4.2266e+08  0.32%   9.1  297s
 17475 12519 4.2345e+08  288  774 4.2402e+08 4.2345e+08  0.13%   9.1  300s
 17482 12524 4.2374e+08  710  771 4.2402e+08 4.2346e+08  0.13%   9.1  305s
 17490 12531 4.2352e+08  493  764 4.2402e+08 4.2346e+08  0.13%  10.5  310s
 17492 12532 4.2346e+08  232  764 4.2402e+08 4.2346e+08  0.13%  10.5  315s
 17494 12536 4.2346e+08   32  763 4.2402e+08 4.2346e+08  0.13%  11.8  322s
 17495 12536 4.2347e+08   32  763 4.2402e+08 4.2346e+08  0.13%  11.8  328s
 17496 12537 4.2346e+08   33  764 4.2402e+08 4.2346e+08  0.13%  11.8  333s
 17505 12548 4.2348e+08   36  767 4.2402e+08 4.2347e+08  0.13%  11.8  339s
 17641 12631 4.2354e+08   70  751 4.2402e+08 4.2347e+08  0.13%  11.9  343s
 17729 12695 4.2357e+08   91  748 4.2402e+08 4.2347e+08  0.13%  11.9  349s
 17917 12822 4.2360e+08  138  714 4.2402e+08 4.2347e+08  0.13%  11.9  355s
 18182 12993 4.2364e+08  209  658 4.2402e+08 4.2347e+08  0.13%  12.0  361s
 18476 13194 4.2369e+08  282  598 4.2402e+08 4.2347e+08  0.13%  12.0  368s
 18807 13409 4.2372e+08  363  543 4.2402e+08 4.2347e+08  0.13%  12.0  374s
 19048 13572 4.2374e+08  423  492 4.2402e+08 4.2347e+08  0.13%  12.0  381s
 19363 13780 4.2377e+08  501  429 4.2402e+08 4.2347e+08  0.13%  12.1  388s
 19736 14033 4.2380e+08  591  381 4.2402e+08 4.2347e+08  0.13%  12.2  395s
H20136 13669                    4.239906e+08 4.2347e+08  0.12%  12.2  411s
H20137 13073                    4.239710e+08 4.2347e+08  0.12%  12.2  411s
 20138 13074 4.2384e+08  693  315 4.2397e+08 4.2347e+08  0.12%  12.2  419s
 20562 13357 4.2388e+08  797  261 4.2397e+08 4.2347e+08  0.12%  12.3  427s
 21013 13646 4.2391e+08  910  202 4.2397e+08 4.2347e+08  0.12%  12.3  435s
 21354 13826 4.2393e+08  979  161 4.2397e+08 4.2347e+08  0.12%  12.4  443s
 21809 14087 4.2356e+08   84  735 4.2397e+08 4.2348e+08  0.12%  12.4  451s
 22272 14394 4.2365e+08  198  657 4.2397e+08 4.2348e+08  0.12%  12.5  460s
 22753 14713 4.2373e+08  320  601 4.2397e+08 4.2348e+08  0.12%  12.5  469s
 23262 15052 4.2379e+08  448  514 4.2397e+08 4.2348e+08  0.12%  12.6  478s
 23795 15410 4.2384e+08  581  420 4.2397e+08 4.2348e+08  0.12%  12.6  486s
 24253 15713 4.2387e+08  692  348 4.2397e+08 4.2348e+08  0.12%  12.6  496s
 24858 16100 4.2393e+08  843  226 4.2397e+08 4.2348e+08  0.12%  12.6  506s
H25485 15349                    4.239534e+08 4.2348e+08  0.11%  12.7  533s
 25583 15320     cutoff 1051      4.2395e+08 4.2348e+08  0.11%  12.7  542s
 26023 15611 4.2362e+08  167  697 4.2395e+08 4.2348e+08  0.11%  12.7  552s
 26717 16066 4.2372e+08  327  600 4.2395e+08 4.2348e+08  0.11%  12.6  563s
 27500 16601 4.2381e+08  523  455 4.2395e+08 4.2348e+08  0.11%  12.6  575s
 28256 17085 4.2387e+08  667  383 4.2395e+08 4.2348e+08  0.11%  12.5  580s
 28421 17212 4.2388e+08  689  368 4.2395e+08 4.2348e+08  0.11%  12.5  591s
 29251 17740 4.2394e+08  879  240 4.2395e+08 4.2348e+08  0.11%  12.4  600s
 29930 18145 4.2357e+08   73  739 4.2395e+08 4.2348e+08  0.11%  12.3  610s
 30646 18617 4.2369e+08  227  667 4.2395e+08 4.2348e+08  0.11%  12.3  619s
 31336 19071 4.2377e+08  325  607 4.2395e+08 4.2348e+08  0.11%  12.2  628s
 31924 19439 4.2382e+08  426  535 4.2395e+08 4.2348e+08  0.11%  12.2  640s
 32206 19622 4.2385e+08  469  503 4.2395e+08 4.2348e+08  0.11%  12.2  648s
 32792 20001 4.2389e+08  566  443 4.2395e+08 4.2348e+08  0.11%  12.2  656s
 33348 20366 4.2394e+08  700  371 4.2395e+08 4.2348e+08  0.11%  12.2  680s
 33350 20371 4.2394e+08  698  372 4.2395e+08 4.2348e+08  0.11%  12.2  688s
 33876 20696 4.2359e+08  119  724 4.2395e+08 4.2348e+08  0.11%  12.2  697s
 34374 21029 4.2367e+08  247  652 4.2395e+08 4.2348e+08  0.11%  12.2  705s
 34375 21029 4.2367e+08  248  652 4.2395e+08 4.2348e+08  0.11%  12.2  716s
 34896 21387 4.2374e+08  355  588 4.2395e+08 4.2348e+08  0.11%  12.2  723s
 35412 21734 4.2378e+08  429  537 4.2395e+08 4.2348e+08  0.11%  12.2  730s
 35963 22081 4.2383e+08  536  462 4.2395e+08 4.2348e+08  0.11%  12.2  737s
 35964 22081 4.2384e+08  537  462 4.2395e+08 4.2348e+08  0.11%  12.2  742s


Solution

  • Gurobi isn't stalling. It has found a solution within 0.11% of optimal and is continuing to try to improve the bound to 0.01%. If you want to stop it sooner, you should change the parameter MIPGap.

    To actually make Gurobi faster, you can try changing other parameters with the Tuning Tool. You best bet is to tighten your model formulation, but that's very problem dependent, and you haven't posted your actual formulation.