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4 replies Latest Post - ‏2013-07-05T14:24:59Z by MFC
MFC
MFC
5 Posts
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Pinned topic How can we set the timeLimit after getting the first feasible solution (CP Improve Solution)

‏2013-07-03T16:54:18Z |

Hi, 

Is there a way of setting the optimization parameters before and after getting the first feasible solution. I prefer to get some feasible solution, but after getting a feasible solution, don't want to spend too much time for improving it. 

So I need something like

TimeLimit (before the first feasible solution) = 1000

TimeLimit (after the first feasible solution) = 500

FailLimit (before the first feasible solution) = 3000

FailLimit (after the first feasible solution) = 600

Seems like the profiler is already keeping these times separately, such as CP Search, CP Improve Solution.

Thanks in advance, 

  • PhilippeLaborie
    PhilippeLaborie
    36 Posts
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    Re: How can we set the timeLimit after getting the first feasible solution (CP Improve Solution)

    ‏2013-07-04T07:12:17Z  in response to MFC

    Hello,

    I suppose from your question that you are using OPL. You can iterate over the solutions and change the limits on the engine after the first solution is found. You can do this with some scripting in you OPL model. For instance:

    main {
      var TimeLimitFirstSolution = 1000;
      var TimeLimitImprovement   = 500;
      var FailLimitFirstSolution = 300000;
      var FailLimitImprovement   = 60000;
      cp.param.TimeLimit = TimeLimitFirstSolution;
      cp.param.FailLimit = FailLimitFirstSolution;
     
      var model = thisOplModel;
      model.generate();
      cp.startNewSearch();
      var nSol = 0;
      writeln("Searching for first solution with initial limits");
      while(cp.next()) {
        if (nSol == 0) {
          writeln("First solution found, changing limits");
          cp.param.TimeLimit = TimeLimitImprovement;
          cp.param.FailLimit = FailLimitImprovement;
          nSol++;
        }      
        model.postProcess();
      }
    }

    Philippe

    • MFC
      MFC
      5 Posts
      ACCEPTED ANSWER

      Re: How can we set the timeLimit after getting the first feasible solution (CP Improve Solution)

      ‏2013-07-05T11:59:45Z  in response to PhilippeLaborie

      Thanks a lot Philippe.

      A quick question about this script: When the (timeLimit and) failLimit are set second time within the if loop, does it reset the previous failures that happened till getting the first solution, and start counting from zero? For example, if numberOfFailures is 40000 when we got the first solution, then is the remaining failLimit for the improvement 60000-40000=20000? 

      Updated on 2013-07-05T12:16:09Z at 2013-07-05T12:16:09Z by MFC
      • PhilippeLaborie
        PhilippeLaborie
        36 Posts
        ACCEPTED ANSWER

        Re: How can we set the timeLimit after getting the first feasible solution (CP Improve Solution)

        ‏2013-07-05T13:21:21Z  in response to MFC

        No, it does not restart counting from 0, it just changes the limit but the reference is always the beginning of the search. Note that you can access the current information on the engine (current number of failures, current time) in order to emulate restarting the limit:

        cp.param.TimeLimit = cp.info.SolveTime     + TimeLimitImprovement;
        cp.param.FailLimit = cp.info.NumberOfFails + FailLimitImprovement;
         

        Philippe

        • MFC
          MFC
          5 Posts
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          Re: How can we set the timeLimit after getting the first feasible solution (CP Improve Solution)

          ‏2013-07-05T14:24:59Z  in response to PhilippeLaborie

          Great! 

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