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Mincost is infeasible or unbounded


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Hello everyone, this is my error message.

Warning: After zero iterations the preprocessor of CPLEX 20.1 concluded that MinCost is infeasible or unbounded.

I think the problems lays in my constraints.

Production_workcenter is 100% incorrect but i’m not sure how to use the subset allowed_product_per_workcenter

Are there other problems ?

Thank you

 

Marc

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Best answer by Marcel Hunting 4 May 2022, 17:29

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Userlevel 4
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Hi @solam. Your model appears to be unbounded, that is, some of the X(i,w,t) or Tr(i,m,l,t) can become very negative. You can check this by (temporarily) adding the following constraint:

TotalCost >= -100000000

If you then solve the model TotalCost will become -100000000.

You declared both variables X and Tr as free variables, so having range (-inf,inf). Are you sure these variables should not be nonnegative?

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Hi Marcel, thank you for answering that fast. Nice catch theses variables should be nonnegative. Now the problem is, the solution is said to be infeasible.

Do you know why ? I’m sure my production capacity constraint is wrong but don’t know how to make it work.

 

Userlevel 3
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Complementing @Marcel Hunting, Inv should be nonnegative too. 

 

With the 3 decision variables nonnegative I was able to run without infeasibilities. Do you have a new scenario? 

And, looking on Production_capacity(w,t), I advise you to use units. For that, you will need create a Quantity with the units you will use on the project, then set on the parameter, variable and contraint ‘unit’ part, example: 

Then, if there is a unit problem with your constraint, AIMMS will give you an error. 

 

Hope that helps. 

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Yes, I was able to run the program. Thank your for your help!

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