How to store a solution from gurobi optimizer in a list in python ?

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Anis Boudieb

2020年09月01日 21:39

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I have an assignment problem where I used gurobi to optimise my model. I have results in this format when I use the optimize() function : 

assign[287,128]:1.0
assign[292,129]:1.0
assign[271,130]:1.0
assign[272,131]:1.0
assign[270,132]:1.0

How do I store them in list ?

new_list = [("287, "128") , ("292", "129")..........]

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• 正式なコメント

  

  Simranjit Kaur

  • Gurobi Staff

  2025年06月23日 03:07 編集済み

  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?.
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  Eli Towle

  • Gurobi Staff

  2020年09月01日 22:49

  Do you want the list to contain the indices of the \( \texttt{assign} \) variables for which the corresponding \( \texttt{assign} \) variable takes a value of 1 at the optimal solution? Assuming you defined your \( \texttt{assign} \) variables like

  assign = m.addVars(...)

  you can do this with a list comprehension:

  new_list = [k for k, v in assign.items() if v.X > 0.5] 

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  Anis Boudieb

  2020年09月02日 15:12

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  Hi Eli,

  I used the list comprehension as you said and my combinations have been stored. Thank you for you help.
  

   

   

   

   

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  Anis Boudieb

  2020年09月02日 18:00

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  Hi Eli,

  I have another question please. How I store the costs related to each variable. 

  By using multidict(), I am attributing costs to each variable as:

  combinations, ms = multidict({k: v for k, v in zip(list3, Costs)})
  x = m.addVars(combinations, name='assign')
  when I print ms I have this:
  
  ('287','128'): 2
  ('292','129'): 3
  ('271','130'): 1
  ('272','131']: 0
      etc....
  
  After running the model I want to store the delays assigned. How is it possible ?
  
  

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  Eli Towle

  • Gurobi Staff

  2020年09月02日 20:33

  Could you clarify what the delays are in your code, and what format you're trying to store them in?

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  Anis Boudieb

  2020年09月02日 21:54

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  I have two lists:

  Costs = [2, 3, 1, 0...]
  list3 = [('287','128'), ('292','129'), ('271','130'), ('272','131')...]

  I am using this code below to assign the cost to each combination. (I have more than thousands combination and associated cost, I just wrote few of them in this example)

  combinations, ms = multidict({k: v for k, v in zip(list3, Costs)})
  

  If I print ms I will have:

  {('287','128'): 2, ('292','129'): 3, ('271','130'): 1, ('272','131'): 0...}

  When I run my model I have this result   :

  assign[287,128]:1.0
  assign[292,129]:1.0
  assign[271,130]:1.0
  assign[272,131]:1.0

  But it does not show the costs associated with every variable assigned after the optimisation, and I would like to store the cost in a new list as :

  new_cost = [2, 3, 1, 0] 

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  Eli Towle

  • Gurobi Staff

  2020年09月02日 22:33

  The construction is basically the same, with the extra step of mapping the keys to the appropriate costs using the \( \texttt{ms} \) dictionary:

  cost_list = [ms[k] for k, v in x.items() if v.X > 0.5]

  Also, I don't see a reason to use multidict here, since you are just constructing a single dictionary. You could instead write

  ms = {k: v for k, v in zip(list3, Costs)}

  to obtain the same \( \texttt{ms} \) dictionary. Then, you can use the \( \texttt{list3} \) list instead of the \( \texttt{combinations} \) list, since these should be the same.

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