Exporting the Reduced (Pre-solved) model

Answered

Prabhu Manyem

July 10, 2022 02:20

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Let us call the model AFTER pre-solving as the "Reduced Model"... How can I get this reduced model?  Is it possible to export this to a file from command line?  Doesn't matter whether I can get this done with or without running the problem to completion.

I have seen this:  https://support.gurobi.com/hc/en-us/articles/360024738352-How-does-presolve-work-  and this:  https://www.gurobi.com/documentation/9.5/refman/py_model_presolve.html

But unfortunately they don't say how to get the Reduced Model from the command line.

Why do I need the reduced model?  So that I don't need to use the presolver repeatedly.

Thanks.

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  Jonasz Staszek

  • Community Moderator

  July 10, 2022 10:58

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  Hi Prabhu,

  you could try:

  reduced_model = model.presolve()
  reduced_model.write("reduced_model.lp")

  Best regards
  Jonasz

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  Prabhu Manyem

  July 11, 2022 00:16

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  Hi Jonasz,  Thank you, but, as I asked in my previous post, is it possible to do all this from the command line?

   

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  Jonasz Staszek

  • Community Moderator

  July 11, 2022 06:58

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  Yes, exactly in the same fashion.

  You first generate the presolved model:

  > reduced_model = model.presolve()

  and then you store it in your desired location:

  > reduced_model.write("reduced_model.lp")

  Best regards,
  Jonasz

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  Gwyneth Butera

  • Gurobi Staff

  July 11, 2022 10:59

  Please also see the Knowledge Base article How does presolve work? for more information.

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  Matthias Miltenberger

  • Gurobi Staff

  July 11, 2022 11:04

  Please note that you need to be in an interactive Python shell to run those commands. Exporting the presolved model does not work directly through the command line with gurobi_cl.

  Cheers,
  Matthias

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  Prabhu Manyem

  July 11, 2022 23:12 Edited

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  Thanks Matthias.. Yes, I should have made it clear that I was talking about the LINUX shell command line (gurobi_cl) -- NOT the Python shell :-)

  Anyway, I got the job done by writing Python code, by following this post by Glockner at Stack Overflow.  Here's my modified code:

  #!/opt/gurobi951/linux64/bin/python3.7
  (Your python3.7 may be located in a different directory.
  So replace the above line accordingly.)
  
  import gurobipy as gp
  from gurobipy import GRB
  
  modello = gp.read("Original_Model.lp")
  reduced_model = modello.presolve()
  reduced_model.write("reduced_model.lp")

  Thanks everyone.

   

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