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Creating set of sets.

  • 19 May 2019
  • 1 reply
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Hi,
I'm making a model of flexible flow shop for academic project and I have a problem with declaring one set(or sets in fact). The set I'm talking about is a set of parallel machins which are bounded to specific stages. It looks more or less like this:
  • t - stage index, t = 1, 2, 3, . . . , k
  • i - machine index, i = 1, 2, 3, . . . , mt (t is upper index)
Do I have to specify every set of machines seperatly for each stage or is there some convinient way of doing it?
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Best answer by deannezhang 20 May 2019, 03:05

Hi,



You do not need to specify every set of machines for each stage, what you can do is to introduce a parameter StageMachineMapping (t,i).



If machine i belongs to stage t, then StageMachineMapping is 1, otherwise it's 0.



Then when you declare your decision variables, for example, JobSchedule(t,i,j), which is to assign job j to machine i on stage t, you want to use StageMachineMapping (t,i) as domain condition of this variable, so for each job j the model will only use a machine i if it belongs to stage t. You also need to use this parameter as domain condition for all variables and constrains when it applies.



Hope this helps.
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Userlevel 3
Hi,

You do not need to specify every set of machines for each stage, what you can do is to introduce a parameter StageMachineMapping (t,i).

If machine i belongs to stage t, then StageMachineMapping is 1, otherwise it's 0.

Then when you declare your decision variables, for example, JobSchedule(t,i,j), which is to assign job j to machine i on stage t, you want to use StageMachineMapping (t,i) as domain condition of this variable, so for each job j the model will only use a machine i if it belongs to stage t. You also need to use this parameter as domain condition for all variables and constrains when it applies.

Hope this helps.

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