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  • having difficulties to execute my VRP model

    From simo@21:1/5 to All on Wed Aug 16 08:13:01 2017
    hello,
    im working on vehicle routing problem , so first of all i putted my model in cplex, and while executing i encounter some errors and i did solve them , so my model was working perfectly for n=10 customers or below , but when i try to execute my model
    for a large number of customers like 35 customers , i encounter no errors and no solution either ,so i need your help, at this moment in the engine log i have this so far:

    tried aggregator 2 times.
    MIP Presolve eliminated 252 rows and 260 columns.
    MIP Presolve modified 7 coefficients.
    Aggregator did 7 substitutions.
    Reduced MIP has 45130 rows, 18634 columns, and 151424 nonzeros.
    Reduced MIP has 9310 binaries, 9072 generals, 0 SOSs, and 0 indicators.
    Elapsed time 10.02 sec. for 6% of probing (10 vars fixed).
    Elapsed time 20.03 sec. for 12% of probing (26 vars fixed).
    Probing fixed 26 vars, tightened 976 bounds.
    Probing time = 21.78 sec.
    Tried aggregator 1 time.
    MIP Presolve eliminated 654 rows and 542 columns.
    MIP Presolve modified 17588 coefficients.
    Reduced MIP has 44476 rows, 18092 columns, and 141698 nonzeros.
    Reduced MIP has 9046 binaries, 9046 generals, 0 SOSs, and 0 indicators. Presolve time = 22.45 sec.
    Probing time = 0.34 sec.
    Clique table members: 83920.
    MIP emphasis: balance optimality and feasibility.
    MIP search method: dynamic search.
    Parallel mode: deterministic, using up to 4 threads.
    Root relaxation solution time = 0.48 sec.
    Nodes Cuts/
    Node Left Objective IInf Best Integer Best Node ItCnt Gap
    0 0 50.9260 428 50.9260 1083
    0 0 cutoff 2110 Elapsed real time = 26.52 sec. (tree size = 0.00 MB, solutions = 0)
    Implied bound cuts applied: 2
    Gomory fractional cuts applied: 4
    Root node processing (before b&c):
    Real time = 4.07
    Parallel b&c, 4 threads:
    Real time = 0.00
    Sync time (average) = 0.00
    Wait time (average) = 0.00
    -------
    Total (root+branch&cut) = 4.07 sec.
    Refine conflict on 10109 members...
    Iteration Max Members Min Members
    1 5055 0
    2 2528 0
    3 1264 0
    4 948 0
    5 790 0
    6 786 0
    7 784 0

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  • From Paul@21:1/5 to simo on Wed Aug 16 14:21:02 2017
    On Wednesday, August 16, 2017 at 11:13:03 AM UTC-4, simo wrote:

    Refine conflict on 10109 members...
    Iteration Max Members Min Members
    1 5055 0
    2 2528 0
    3 1264 0
    4 948 0
    5 790 0
    6 786 0
    7 784 0

    This output seems to indicate that the conflict refiner was run. Did your code trigger it?

    Assuming that it was run on the same problem for which the rest of the log applies, it would seem your model is infeasible. If you think that is incorrect, can you write down a feasible solution? (It does not matter how bad the solution is, just that it
    is feasible.) If so, try fixing the variables to those values (by setting lower bound = upper bound = value) and run the conflict refiner on the modified model. Either it was say no conflict (in which case the model really is feasible) or else it should
    point you to some violated constraints (which you should check for errors).

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  • From [email protected]@21:1/5 to All on Wed Aug 16 17:12:03 2017
    Le mercredi 16 août 2017 22:21:06 UTC+1, Paul a écrit :
    On Wednesday, August 16, 2017 at 11:13:03 AM UTC-4, simo wrote:

    Refine conflict on 10109 members...
    Iteration Max Members Min Members
    1 5055 0
    2 2528 0
    3 1264 0
    4 948 0
    5 790 0
    6 786 0
    7 784 0


    thank you for your answer , in fact my model works so well , i took an example of n=10 customers and i realize that i had an optimale solution , so far all my variables are bounded , unless my objective function , so i tried to fix this objective
    function by setting lower bound and upper bound , but i still have the same problem and i don't know how to solve it ,and of course my code trigger the conflict refiner

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