Infeasibility Relaxation with Gurobi

Answered

Nitin Singh

December 05, 2023 05:42 Edited

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I have an infeasible model. I am attempting to perform Infeasibility Relaxation with model.feasRelax. 
While doing that, I am trying to keep a certain number of constraints outside of the analysis i.e. they can't be relaxed. 
Below is my pseudocode:

# constraint filtering condition
constraints_ls = [i for i in self.gurobi_model.getConstrs() if 'xyz_upper_bound' not in i.constrname if 'xyz_lower_bound' not in i.constrname]

# feasibility relaxation
self.gurobi_model.feasRelax(
                relaxobjtype=0, minrelax=False, vars=False, lbpen=None, ubpen=None,
                constrs=constraints_ls, rhspen=None)
            )

While, trying to do this, I get the following error:

TypeError: object of type 'bool' has no len()

I am not sure what is causing it. Could someone help me with it?
What more information would you need to help me?

Thanks

Related to

• FeasRelax

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  Riley Clement

  • Gurobi Staff

  December 05, 2023 05:55

  Hi Nitin,

  Note that in the documentation you linked it states the following for the vars parameter:

  vars: Variables whose bounds are allowed to be violated. 

  The function is expecting a collection of variables, such as a list, which is why vars=False is causing an error.

  - Riley

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  Nitin Singh

  December 05, 2023 05:57

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  But what if I don't want the relaxation to play with the variable bounds, but only the RHS of the constraints? 

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  Riley Clement

  • Gurobi Staff

  December 05, 2023 05:59

  Passing an empty list as an argument is acceptable.

  - Riley

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  Nitin Singh

  December 05, 2023 06:01

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  I just did that. Thanks.
  My bad that I thought it was a boolean.

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  Nitin Singh

  December 05, 2023 07:19 Edited

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  Riley Clement
  I have a follow up question on this. For the same infeasible model (now I am not filtering down any constraint for this relaxation exercise):
  If I try model.feasRelax as follows:

  self.gurobi_model.feasRelax(
                  relaxobjtype=0, minrelax=False, vars=[], lbpen=None, ubpen=None,
                  constrs=self.gurobi_model.getConstrs(), rhspen=None
              )

  The model still remains infeasible, however if I use the model.feasRelaxS as:

  self.gurobi_model.feasRelaxS(
                  relaxobjtype=0, minrelax=False, vrelax=False, crelax=True
              )

  , I am able to arrive at a possible feasibility relaxation. 
  
  What is likely to cause this difference in the behavior?
  
  

  Thanks

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  Riley Clement

  • Gurobi Staff

  December 05, 2023 08:21

  Hi Nitin,

  The rhspen parameter needs values if you are providing constraints to be relaxed.

  rhspen: Penalty for violating a linear constraint. One entry for each constraint in argument constrs. 

  If you use

  rhspen=[1]*len(m.getConstrs())

  then you will get equivalent results to feasRelaxS.

  - Riley

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