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gurobi set initial solution slow down the solver

Ongoing
Jiangfei DUAN
Gurobi-versary
Conversationalist
Curious

Hi, gurobi community,

I am trying to use an initial solution to speed up the solver (MILP model). But in my case, the initial solution sometimes slow down the solving speed.  Here are my two result.

I wonder, why could initial solution slow down gurobi solver?

Thanks a lot!

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Comments

4 comments

Date Votes
  • Official comment
    Simranjit Kaur
    Gurobi Staff Gurobi Staff
    This post is more than three years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum. Or why not try our AI Gurobot?.
  • Silke Horn
    Gurobi Staff Gurobi Staff

    Hi,

    Did you set a full MIP start or a partial one? Sometimes completing a partial MIP start can take considerable time.

    Apart from that, it is difficult to say more without a log file.

    Silke

    0
  • Jiangfei DUAN
    • Edited
    Gurobi-versary
    Conversationalist
    Curious

    Hi,

    Thanks for your reply.

    I set a partial solution, but it solves the partial solution quickly, and here is my log.

    The log without setting initial solution

    Academic license - for non-commercial use only - expires 2021-03-19
    Using license file /home/duanjiangfei/gurobi.lic
    Gurobi Optimizer version 9.1.1 build v9.1.1rc0 (linux64)
    Thread count: 16 physical cores, 32 logical processors, using up to 32 threads
    Optimize a model with 77563 rows, 5257 columns and 314269 nonzeros
    Model fingerprint: 0xd279248c
    Variable types: 1406 continuous, 3851 integer (3843 binary)
    Coefficient statistics:
    Matrix range [6e-05, 2e+04]
    Objective range [1e+00, 2e+01]
    Bounds range [1e+00, 7e+00]
    RHS range [1e+00, 3e+04]
    Presolve removed 8769 rows and 153 columns
    Presolve time: 1.52s
    Presolved: 68794 rows, 5104 columns, 280004 nonzeros
    Variable types: 750 continuous, 4354 integer (3835 binary)
    Root relaxation: objective 0.000000e+00, 4599 iterations, 0.36 seconds
    Nodes | Current Node | Objective Bounds | Work
    Expl Unexpl | Obj Depth IntInf | Incumbent BestBd Gap | It/Node Time
    000.000000120 - 0.00000 - - 4s
    H 0 0 34.0000000 0.00000 100% - 4s
    000.00000047834.000000.00000100% - 9s
    000.00000048234.000000.00000100% - 10s
    H 0 0 28.8901786 0.00000 100% - 19s
    000.00000029028.890180.00000100% - 23s
    000.00000029428.890180.00000100% - 24s
    000.0000009028.890180.00000100% - 36s
    H 0 0 28.8901786 0.00000 100% - 36s
    000.00000018228.890180.00000100% - 36s
    000.00000019328.890180.00000100% - 38s
    H 0 0 21.2723214 0.00000 100% - 42s
    000.0000009221.272320.00000100% - 43s
    000.00000031721.272320.00000100% - 44s
    000.00000011921.272320.00000100% - 51s
    000.00000011921.272320.00000100% - 53s
    020.0000009821.272320.00000100% - 57s
    15290.00000431321.272320.00000100% 406 60s
    78750.00000828821.272320.00000100% 338 68s
    H 84 75 21.2723214 0.00000 100% 348 68s
    94820.00000928821.272320.00000100% 338 73s
    111880.00000107921.272320.00000100% 361 75s
    1801650.000001316421.272320.00000100% 367 80s
    H 181 165 21.2723214 0.00000 100% 365 80s
    H 211 165 21.2723214 0.00000 100% 351 80s
    H 360 260 17.4723214 0.00000 100% 314 93s
    4293040.000002116317.472320.00000100% 294 97s
    5423860.000002318017.472320.00000100% 314 104s
    740488 cutoff 3017.472320.00000100% 295 110s
    10085030.000001817517.472320.00000100% 284 123s
    10776470.000001918517.472320.00000100% 277 131s
    1403830 cutoff 2517.472320.00000100% 288 141s
    177110230.000001225517.472320.00000100% 310 153s
    2242116013.483331411917.472320.00000100% 308 163s
    26871421 cutoff 2117.472320.00000100% 326 177s
    346514872.765623231817.472320.00000100% 311 206s
    H 3504 1487 17.3629464 0.00000 100% 309 206s
    H 3573 1217 13.2723214 0.00000 100% 312 206s
    361813737.125001921913.272320.00000100% 312 222s
    432113746.400001011913.272320.00000100% 313 230s
    432313757.80937919613.272320.00000100% 313 257s
    4324137610.625002570513.272320.00000100% 313 282s
    432513770.0000016107213.272320.00000100% 313 286s
    432613770.000001517913.272320.00000100% 313 295s
    433013800.00000277913.272320.00000100% 312 305s
    433413839.375002115113.272320.00000100% 312 323s
    433613840.000001724013.272320.00000100% 312 327s
    434013877.87500164013.272320.00000100% 312 331s
    H 4341 1317 13.2723214 0.00000 100% 312 344s
    H 4341 1251 13.2723214 0.00000 100% 312 344s
    H 4341 1188 13.2723214 0.00000 100% 312 344s
    4342118911.400003116113.272320.00000100% 312 347s
    434411901.339293015613.272320.00000100% 311 352s
    434511940.000001025113.272320.00000100% 358 363s
    434711970.000001157013.272320.00000100% 358 385s
    435112010.000001257613.272320.00000100% 358 400s
    435912050.000001335813.272320.00000100% 358 407s
    437212120.000001432613.272320.00000100% 358 425s
    H 4375 1151 13.2723214 0.00000 100% 358 425s
    438811560.000001519813.272320.00000100% 359 434s
    440411610.000001538913.272320.00000100% 359 471s
    442011650.000001642513.272320.00000100% 363 493s
    443611720.000001626013.272320.00000100% 364 499s
    446111814.687501741113.272320.00000100% 365 511s
    H 4477 1119 13.2723214 0.00000 100% 368 511s
    448811270.000001737813.272320.00000100% 369 518s
    451411308.925001858113.272320.00000100% 375 540s
    453311434.687501841313.272320.00000100% 375 546s
    457211389.987742069813.272320.00000100% 376 558s
    H 4595 1077 13.2589286 0.00000 100% 375 558s
    460010878.925002055213.258930.00000100% 375 563s
    H 4655 1038 13.2589285 0.00000 100% 375 573s
    H 4727 966 13.2580915 0.00000 100% 375 573s
    H 4740 914 13.2299107 0.00000 100% 375 573s
    47469579.215992568013.229910.00000100% 375 581s
    48459424.9359527136913.229910.00000100% 376 601s
    H 4885 885 13.2254464 0.00000 100% 376 601s
    4891936 infeasible 3413.225450.00000100% 376 613s
    50529895.312501954913.225450.00000100% 373 623s
    52361073 infeasible 2313.225450.00000100% 368 631s
    H 5242 1029 13.2254464 0.00000 100% 369 631s
    H 5264 983 13.2254464 0.00000 100% 367 631s
    H 5266 944 13.2254463 0.00000 100% 367 632s
    H 5345 882 13.2254463 0.00000 100% 365 632s
    54409639.204462180113.225450.00000100% 360 644s
    H 5462 922 13.1160714 0.00000 100% 359 644s
    H 5592 846 13.1160714 0.00000 100% 355 644s
    H 5638 800 13.0066964 0.00000 100% 354 644s
    56468219.204462582313.006700.00000100% 355 653s
    577783013.004463878713.006700.00000100% 357 665s
    591779513.004466664313.006700.00000100% 359 694s
    H 5946 756 12.7879456 0.00000 100% 360 694s
    5976776 cutoff 6712.787950.00000100% 361 705s
    61178214.037502734512.787950.00000100% 361 719s
    6240842 infeasible 3012.787950.00000100% 362 731s
    63618673.937502250512.787950.00000100% 368 745s
    64548879.200002387512.787950.00000100% 372 758s
    66028593.937502359212.787950.00000100% 376 771s
    6706859 infeasible 2412.787950.00000100% 378 784s
    6874830 infeasible 2312.787950.00000100% 382 801s
    69718775.312502649512.787950.00000100% 385 815s
    71548604.687502572512.787950.00000100% 388 829s
    7299856 infeasible 2712.787950.00000100% 392 845s
    74018915.312502328712.787950.00000100% 395 859s
    7571882 cutoff 2512.787950.00000100% 399 874s
    77728680.131341936812.787950.00000100% 401 900s
    78558830.306452031812.787950.00000100% 403 915s
    8021873 infeasible 2612.787950.00000100% 407 933s
    82088699.987742845412.787950.00000100% 407 951s
    83448797.6927033115412.787950.00000100% 409 967s
    85738827.6927036130612.787950.00000100% 411 997s
    87089337.6927037134512.787950.00000100% 410 1014s
    8951965 cutoff 4012.787950.00000100% 412 1039s
    91779804.037502418912.787950.00000100% 412 1085s
    93271015 infeasible 2512.787950.00000100% 412 1107s
    9669105910.625002342112.787950.1451698.9% 411 1129s
    100291072 infeasible 2212.787950.1741998.6% 409 1151s
    1041610928.075002564412.787950.2909997.7% 408 1174s
    1089111358.550001934012.787950.2909997.7% 404 1197s
    11328113611.250002855712.787951.2193590.5% 402 1222s
    116621166 infeasible 3712.787953.5625072.1% 403 1246s
    1195011948.002233063812.787953.5625072.1% 402 1270s
    122961224 cutoff 2812.787953.5625072.1% 400 1296s
    1267712309.3222930105712.787953.5625072.1% 398 1322s
    1303312648.008932988412.787953.8000070.3% 398 1350s
    1342212578.0089340120612.787953.8000070.3% 399 1380s
    1390812673.9811424121512.787953.9375069.2% 398 1410s
    14397131710.500002763512.787953.9375069.2% 399 1442s
    1502813334.722982548612.787953.9375069.2% 397 1474s
    1563313174.380243075012.787953.9375069.2% 395 1509s
    164041307 cutoff 3812.787954.2750066.6% 391 1544s
    1711412728.075002546912.787954.7250063.1% 387 1584s
    1758313888.075002456512.787955.0000060.9% 385 1626s
    1910812858.800003557612.787955.3125058.5% 369 1667s
    2038812775.6250031101012.787955.6250056.0% 359 1711s
    2049113339.775001970612.787956.4285749.7% 359 1749s
    213561425 cutoff 3312.787957.6898639.9% 354 1786s
    221381391 cutoff 3412.787957.6934039.8% 350 1842s
    234851471 cutoff 2412.787958.0000037.4% 344 1873s
    244291434 cutoff 3112.787958.0067037.4% 337 1904s
    2560313998.2063249107012.787958.0111637.4% 330 1936s
    272611283 cutoff 3212.787958.0111637.4% 317 1964s
    28528122010.625002437312.787958.3780434.5% 308 1992s
    2974611578.925002147112.787958.8000031.2% 300 2022s
    3113312789.3452728117112.787959.0250029.4% 291 2053s
    331121253 cutoff 3312.787959.4500026.1% 279 2085s
    349621244 infeasible 2512.787959.4500026.1% 270 2114s
    36777118910.625003794512.787959.4500026.1% 262 2143s
    387551107 infeasible 8312.7879510.6250016.9% 254 2177s
    41562908 infeasible 3612.7879510.6250016.9% 242 2208s
    4415774812.187992594912.7879510.6250016.9% 232 2234s
    4591371512.217865550612.7879511.2500012.0% 226 2261s
    4672069411.2500056101112.7879511.2500012.0% 224 2289s
    4872538311.250005277612.7879511.2500012.0% 218 2317s
    506688412.672933684112.7879511.2500012.0% 213 2333s
    515340 infeasible 3712.7879512.200004.60% 211 2338s
    Cutting planes:
    Cover: 2
    Implied bound: 20
    Clique: 1
    MIR: 1
    Flow cover: 2
    GUB cover: 1
    Inf proof: 3
    RLT: 161
    Explored 51707 nodes (10953536 simplex iterations) in 2338.39 seconds
    Thread count was 32 (of 32 available processors)
    Solution count 10: 12.7879 13.0067 13.1161 ... 13.2299
    Optimal solution found (tolerance 1.00e-04)
    Best objective 1.278794561044e+01, best bound 1.278794561044e+01, gap 0.0000%
    Warning: variables 1507 and 1707 have the same name "delta_c[0,0]"
    Warning: default variable names used to write solution file
    dur：0.799
    The log with setting initial solution (partial log since it costs too much time to run)
    Academic license - for non-commercial use only - expires 2021-03-19
    Using license file /home/duanjiangfei/gurobi.lic
    >>> Set initial solution!
    Gurobi Optimizer version 9.1.1 build v9.1.1rc0 (linux64)
    Thread count: 16 physical cores, 32 logical processors, using up to 32 threads
    Optimize a model with 77563 rows, 5257 columns and 314269 nonzeros
    Model fingerprint: 0xc0f5c681
    Variable types: 1406 continuous, 3851 integer (3843 binary)
    Coefficient statistics:
    Matrix range [6e-05, 2e+04]
    Objective range [1e+00, 2e+01]
    Bounds range [1e+00, 7e+00]
    RHS range [1e+00, 3e+04]
    User MIP start produced solution with objective 15.0469 (0.15s)
    User MIP start produced solution with objective 14.75 (0.16s)
    Loaded user MIP start with objective 14.75
    Presolve removed 8769 rows and 153 columns
    Presolve time: 1.55s
    Presolved: 68794 rows, 5104 columns, 280004 nonzeros
    Variable types: 750 continuous, 4354 integer (3835 binary)
    Root relaxation: objective 0.000000e+00, 4599 iterations, 0.37 seconds
    Nodes | Current Node | Objective Bounds | Work
    Expl Unexpl | Obj Depth IntInf | Incumbent BestBd Gap | It/Node Time
    000.00000012014.750000.00000100% - 4s
    000.00000045714.750000.00000100% - 8s
    000.00000045714.750000.00000100% - 8s
    000.00000026214.750000.00000100% - 16s
    000.00000016414.750000.00000100% - 23s
    000.00000044414.750000.00000100% - 28s
    000.0000009514.750000.00000100% - 33s
    000.0000009214.750000.00000100% - 34s
    000.00000014514.750000.00000100% - 35s
    000.00000022814.750000.00000100% - 35s
    000.00000023614.750000.00000100% - 38s
    000.00000014214.750000.00000100% - 41s
    020.00000014214.750000.00000100% - 46s
    370.00000228914.750000.00000100% 1905 50s
    75820.00000726714.750000.00000100% 415 56s
    H 136 134 13.4910714 0.00000 100% 303 69s
    1522190.000001020613.491070.00000100% 283 71s
    H 269 235 13.2723214 0.00000 100% 233 93s
    H 283 235 13.1272321 0.00000 100% 235 93s
    2873260.000001618513.127230.00000100% 233 104s
    4205587.476672112613.127230.00000100% 215 110s
    761796 infeasible 913.127230.00000100% 185 117s
    1144988 infeasible 1713.127230.00000100% 177 124s
    153512539.375002013613.127230.00000100% 178 132s
    212913020.000002125213.127230.00000100% 183 155s
    22841745 infeasible 2713.127230.00000100% 186 166s
    317225953.750002724613.127230.00000100% 185 177s
    450825968.4000020714213.127230.00000100% 168 186s
    4510259711.250002312413.127230.00000100% 168 213s
    4511259811.800009525113.127230.00000100% 168 225s
    4514260010.0000010426413.127230.00000100% 168 230s
    4516260111.25000244813.127230.00000100% 168 235s
    451926038.400002067313.127230.00000100% 168 242s
    452126058.400001948613.127230.00000100% 168 249s
    452226050.00000298313.127230.00000100% 167 250s
    452326060.000004323913.127230.00000100% 167 260s
    4525260713.0729220924213.127230.00000100% 167 265s
    452826090.000002927813.127230.00000100% 167 272s
    452926104.200005327713.127230.00000100% 167 279s
    453026113.8000021921813.127230.00000100% 167 285s
    453226150.000001021113.127230.00000100% 209 313s
    453426170.000001114313.127230.00000100% 209 322s
    453826220.000001214113.127230.00000100% 209 329s
    454526290.00000139213.127230.00000100% 209 340s
    455826370.00000148813.127230.00000100% 210 357s
    457426460.000001514213.127230.00000100% 211 362s
    459026510.000001510613.127230.00000100% 212 367s
    460626570.000001620413.127230.00000100% 212 370s
    464726780.273871724213.127230.00000100% 214 384s
    467226790.000001726213.127230.00000100% 214 392s
    469726780.000001824713.127230.00000100% 217 438s
    472127230.290991936413.127230.00000100% 223 451s
    488527014.687502166113.127230.00000100% 227 472s
    499227548.800002346213.127230.00000100% 230 486s
    519827778.800002648913.127230.00000100% 233 506s
    5409290613.024743171413.127230.00000100% 242 524s
    5680308913.006704547413.127230.00000100% 246 563s
    607330560.000002018513.127230.00000100% 242 587s
    628932420.000002340713.127230.00000100% 243 607s
    H 6456 3054 13.1082589 0.00000 100% 246 607s
    6648351313.008934044113.108260.00000100% 243 633s
    H 6664 3380 13.0948661 0.00000 100% 243 633s
    H 6727 3241 13.0926339 0.00000 100% 241 633s
    H 7301 2989 13.0803571 0.00000 100% 234 663s
    H 7308 2879 13.0789621 0.00000 100% 234 663s
    79252985 cutoff 19813.078960.00000100% 228 686s
    8590294013.006703148413.078960.00000100% 222 711s
    900332108.528464746713.078960.00000100% 222 736s
    960936264.9875020111013.078960.00000100% 221 769s
    10474367010.625001864613.078960.00000100% 218 794s
    H11089 2854 13.0652902 0.00000 100% 219 824s
    1135429526.032973758313.065290.00000100% 219 855s
    11903327213.008932748213.065290.00000100% 226 887s
    1250535448.925001975413.065290.00000100% 230 920s
    1318638200.000003238813.065290.00000100% 234 954s
    137584121 cutoff 3013.065290.00000100% 238 988s
    1442241790.000002128713.065290.00000100% 242 1027s
    1473744627.513642638213.065290.00000100% 244 1066s
    1543847190.000002763813.065290.00000100% 247 1118s
    H15447 4527 13.0516183 0.00000 100% 248 1118s
    H15607 4346 13.0379465 0.00000 100% 248 1118s
    1594448454.687503017513.037950.00000100% 248 1173s
    169565298 cutoff 3513.037950.00000100% 251 1218s
    H16957 5271 13.0379464 0.00000 100% 251 1218s
    1803956029.303992169813.037950.00000100% 254 1266s
    1899760768.800002855813.037950.00000100% 254 1311s
    2008464949.200003972713.037950.00000100% 257 1360s
    212437048 cutoff 3013.037950.00000100% 258 1426s
    2266175299.025003355213.037950.00000100% 259 1474s
    2390177510.337842768013.037950.00000100% 260 1523s
    2451183583.937502557113.037950.00000100% 262 1582s
    25985852513.015185375613.037950.00000100% 263 1650s
    Jiangfei
     
    0
  • Silke Horn
    Gurobi Staff Gurobi Staff

    Hi Jiangfei,

    Thanks for pasting the logs. Unfortunately, they are partly illegible because of missing spaces. For example, consider this line:

    000.00000047834.000000.00000100% - 9s

    I can only guess where the spaces between the numbers have been.

     

    Anyway, I would assume that the difference in running time is due to luck. It looks as though Gurobi needs to traverse the entire branch & bound tree in the first log before finishing with an optimal solution. (The numbers in the first column decrease quickly in the last two lines of the branch & bound log.)

    With the MIP start, the solver uses a different path for which it takes longer / more nodes to traverse the full tree.

    To test this hypothesis, you could try running both settings with different random seeds to see how this affects the behavior.

    Silke

    0

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