Delete a Constraint

Answered

Cris

• October 26, 2020 16:00

Hello, I have a column generation problem. I am working matrix and I would like delete a constraint to create another new. I would like to know what is the correct option to do this. I saw in documentation 

model.remove(model.getConstrs()[1:3])

but in each iteration y generate more constrains so I will not know the correct i and j.

I would like to know if I use

model.remove(model.getConstrs())

It clears all restrictions in my model. 

Best regards and thanks

 

0

• Official comment

  

  Simranjit Kaur

  Gurobi Staff

  • December 06, 2024 00:40

  This post is more than three years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum. Or why not try our AI Gurobot?.
• 

  Jaromił Najman

  Gurobi Staff

  • October 27, 2020 12:26
  • Edited

  Hi Cris,

  Yes,

  model.remove(model.getConstrs())

  removes all constraints from your model.

  In order to check what your problem looks like after you removed only a few or all constraints, you can use the Model.write() to write an LP file and examine the file to see whether all desired constraints have been removed.

  Best regards,
  Jaromił

  0
• 

  Cris

  • October 27, 2020 14:10

  

  

  

  Thanks for your answer Jaromił.

  I Have a question yet. If I call my constraints 

  master.update()
  
  # Restricciones
  R1m = master.addConstrs((quicksum(s[k,t] for k in K) <= PAt[t]) for t in T)
  R2m = master.addConstrs((s[k,t] <= M_grande * z[k,t]) for k in K for t in T)
  R3m = master.addConstrs((quicksum(Rt[k][m]*s[k,t] for k in K) >= D[m][t]) for m in M for t in T) # Restricción Auxiliar

  There is an option to delete just the R3m??. Something like this

  model.remove(model.getConstrs(R3m))

  I dont know the correct sintax to do that.

  (I am using benders decomposition and I need a first solution so I tryed to do some cuts with R3m and then I need delete it)

   

  Best regards and thanks for your answer

  0
• 

  Jaromił Najman

  Gurobi Staff

  • October 27, 2020 15:31

  Hi Cris,

  You can use

  model.remove(R3m)

  to remove the \(\texttt{R3m}\) constraints only.

  I would again use the Model.write() function to double check whether the correct constraints have been removed.

  Best regards,
  Jaromił

  0
• 

  Cris

  • October 27, 2020 17:56

  

  

  

  Thanks for your answer. I try to used Model.write() but I wasn´t too sure of how. I read the link but I wasn´t to clear how to do It. I will try with 

  model.remove(R3m)

  Thanks for your help 

  0
• 

  Jaromił Najman

  Gurobi Staff

  • October 28, 2020 08:03

  Hi Cris,

  The Model.write() function can be used as

  model.write("my_LP_before_remove.lp")
  model.remove(R3m)
  model.write("my_LP_after_remove.lp")

  The above will generate 2 LP files. You can use the \(\texttt{write}\) function to also write different files. All are summarized in the documentation of the \(\texttt{write}\) function.

  Best regards,
  Jaromił

   

  0
• 

  Cris

  • October 28, 2020 13:59

  

  

  

  Thanks for your help Jaromił. I am going to see it right now

  Best regards

  Cristian

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