Decision Optimization

Decision Optimization

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  • 1.  Change CPLEX parameters after a certain time limit has reached

    Posted 10/17/21 06:30 PM
    Hi,

    I would like to change certain parameters during the B&B process in Java API and was wondering what could be the most efficient way to do so. 

    Suppose I start my solution process by setting RINS parameter as 250 cplex.setParam(IloCplex.Param.MIP.Strategy.RINSHeur, 250)

    Then, I intend to update this parameter, say after 5 minutes later. My question might be more related to coding rather than CPLEX, but I thought that someone might have already done this in the CPLEX community. 

    I would appreciate any help.

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    S Y
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    #DecisionOptimization


  • 2.  RE: Change CPLEX parameters after a certain time limit has reached

    Posted 10/18/21 03:19 AM
    Hi,

    what you could do is set a time limit , solve and then solve again with the new value

    See in OPL what you also could do in java

    int nbKids=300;
float costBus40=500;
float costBus30=400;
 
dvar int+ nbBus40;
dvar int+ nbBus30;
 
minimize
 costBus40*nbBus40  +nbBus30*costBus30;
 
subject to
{
 40*nbBus40+nbBus30*30>=nbKids;
} 


main
{
  thisOplModel.generate();
  cplex.rinsheur=250;
  cplex.tilim=5*60;
  cplex.solve();
  cplex.rinsheur=100; // new value;
}​


    ------------------------------
    [Alex] [Fleischer]
    [EMEA CPLEX Optimization Technical Sales]
    [IBM]
    ------------------------------



  • 3.  RE: Change CPLEX parameters after a certain time limit has reached

    Posted 10/18/21 09:09 AM
    Edited by System Admin 01/20/23 04:46 PM
    When I call cplex.solve() again, doesn't the B&B process start all over again? or Does it continue where it is left?

    As far as I know, when I add a new constraint to an existing model, it restarts the solution process. So wouldn't changing the CPLEX parameters in this way restart everything? 

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    S Y
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    Original Message


  • 4.  RE: Change CPLEX parameters after a certain time limit has reached

    Posted 10/18/21 09:16 AM
    Hi,

    it will go on from previous solution.

    See https://github.com/AlexFleischerParis/zooopl/blob/master/zoogetsolutiononebyone.mod

    regards

    ------------------------------
    [Alex] [Fleischer]
    [EMEA CPLEX Optimization Technical Sales]
    [IBM]
    ------------------------------

    Original Message


  • 5.  RE: Change CPLEX parameters after a certain time limit has reached

    Posted 10/18/21 09:21 AM
    Hi,

    Thanks for letting me know.

    Just to be on the same page, adding a new constraint restarts everything, doesn't it? I am not referring to any callback function. If I add a hard constraint into my model, that destroys the current tree and creates a new one from the scratch, right?

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    S Y
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    Original Message


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