Decision Optimization

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  • 1.  Modelling Job Shop Scheduling Variant

    Posted Fri September 16, 2022 07:14 AM
    Edited by System Fri January 20, 2023 04:29 PM
    Hi All,

    I have a problem to schedule set of tasks to staffs instead of machines in job shop scheduling. tasks have precedence relations, it require specific skill and its duration is known. we have numerous staffs in each skill. How to build the schedule optimally with an objective to minimize the unassigned tasks and staffs used respecting the precedence constraints, one staff can take only one task at a time (non-overlap)? Please can you share your thoughts?


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    Shah
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    #DecisionOptimization


  • 2.  RE: Modelling Job Shop Scheduling Variant

    Posted Fri September 16, 2022 12:08 PM
    Edited by System Fri January 20, 2023 04:46 PM
    Dear Shah,

    You can try modeling your problem using:
    - optional interval vars  that represent each task
    - optional interval vars that represent the realization of each task by a specific staff (if its skills allow it).
    - for each task interval var, there must be an 'alternative' constraint that forces one of the realization interval to be present (one staff does the job)
    - for each staff, there must be a sequence var that contains all its realization intervals  and a noOverlap constraint which ensures that it won't perform two tasks simultaneously.
    You can compute your objectives with:
      - the sum of the presence attributes of each task intervals
      - the number of non empty staff sequence vars
    I hope it helps.

          Cheers,


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    Renaud Dumeur
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  • 3.  RE: Modelling Job Shop Scheduling Variant

    Posted Sat September 17, 2022 02:13 AM
    Thanks Renaud!

    by any chance do you have an example or any material for the above kind of a problem. That would be helpful.


    shah

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    Shah
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  • 4.  RE: Modelling Job Shop Scheduling Variant

    Posted Sun September 18, 2022 10:17 AM
    Dear Shah,

    You can have a look at the OPL examples described here: https://www.ibm.com/docs/en/icos/20.1.0?topic=programming-scheduling-examples#descriptiveTopic1204630323463__section1204631745558

    in particular, the  sched_optional model assigns tasks to workers with specific skills (similar to what you want to do). 
    For your particular problem each "master" interval of alternative constraints will have to be optional, since some task may not be executed.
    And of course, you can remove the continuity constraints which have no use in your problem.
    I hope this helps,


    Cheers,
    Cheers,

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    Renaud Dumeur
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