Running multiple (unrelated) LP models

Answered

Nan D

October 20, 2023 07:22

• 
• 
• 

Hi, I would like to run multiple LP models automatically one after the other in Python (so not parallel). I will use a for loop for this and thus create a new LP model and solve it in each iteration of the for loop. Now I’m wondering: do I have to reset the Gurobipy Model in each iteration of the for loop? I searched in the forum and documentation and found the model.dispose() and model.reset() options, but I do not see their differences and use cases. Or could i just create a new model through model=gurobipy.Model() at the start of each iteration of the for loop? Thank you!

Related to

• Python

0

• 

  Mario Ruthmair

  • Gurobi Staff

  October 20, 2023 12:42

  Hi Nan,

  If the models are completely different from each other and you have to create them from scratch in each iteration, then you should create a new model at the beginning of your loop iteration and dispose of it at the end. This can be automated by using Python's context manager. The method model.reset() only resets the solution progress, the model formulation stays the same.
  Note that each model requires a Gurobi environment (e.g., for licensing), but the same environment can be used for all the models.
  You might use something like the following:

  import gurobipy as gp
  
  ...
  
  with gp.Env() as env:
    # The environment is disposed of automatically through the context manager
    # upon leaving this block.
    for i in range(N):
      with gp.Model(env=env) as model:
        # 'model' is now an instance tied to the enclosing Env object 'env'.
        # The model is disposed of automatically through the context manager
        # upon leaving this block.
        model.addVars(...)
        ...
        model.optimize()
        ...

  In this article, there are a few further hints to clean up your models and environments.

  1
• 

  Nan D

  October 26, 2023 07:58

  • 
  • 
  • 

  Hi Mario, thank you for your answer! It has gotten much clearer now what to do. I do wonder: why do we need a Gurobi Env for this use case? It’s the first time I see it, although I have solved other LP models with Gurobi. Thank you for your answer!

  0
• 

  Riley Clement

  • Gurobi Staff

  October 26, 2023 11:07

  Hi Nan,

  Mario is away for a few days so I'll jump in.  Every time you solve a model with Gurobi you will have used a Gurobi Env.  If you didn't explicitly create one then a default environment would have been used.  It is often not necessary to explicitly create an environment but it is good practice.

  You can learn more about this here:
  How do I manage Gurobi environments in gurobipy? 

  - Riley

   

  1

Please sign in to leave a comment.