Copying Model

回答済み

Amin Ahmadi

2021年01月17日 17:08 編集済み

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Hello,

I generate a model with several decision variables and constraints. Let's call it Model_1. Next, I want to use Model_1 and add  new constraints to it in a while loop. However, after the loop, I want to work with the initial Model_1 without those extra constraints that I have added in the while loop. Can I make a copy of a Model_1 with Model_1.copy() and call it Model_2. Are all decision variables and constraints of Model_1 are in Model_2? How can I call decision variables and constraints of Model_2 in the while loop? 

Model_1=Model()

x={}

for i in range(I):
      x[i]=Model_1.addVar()

Model_1.addConstr()
Model_2=Model_1.copy()

while iteration<10:
      Add constraints to Model_2 
      Model_2.update()
      Model_2.optimize()

Back to Model_1

Thanks.

0

• 正式なコメント

  

  Simranjit Kaur

  • Gurobi Staff

  2025年06月23日 03:02 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

  2021年01月18日 20:20

  Yes, you can use Model.copy() for this purpose. However, as you noticed, copying a model doesn't give you local Python variables for the new model's Var/Constr objects. You can construct these data structures yourself using Model.getVarByName() and Model.getConstrByName().

  Another (probably easier) approach is to only create one model, then use Model.remove() to remove the extra constraints once your loop completes. E.g.:

  import gurobipy as gp
  
  # Model: min{x : x >= 0}
  m = gp.Model()
  x = m.addVar(obj=1, name='x')
  
  # Optimal objective is 0
  m.optimize()
  
  # Add constraints in loop
  cons = []
  for i in range(10):
      # Add each Constr object to cons list
      cons.append(m.addConstr(x >= i + 1))
      # Optimal objective is i+1
      m.optimize()
  
  # Remove constraints added in loop above
  for c in cons:
      m.remove(c)
  
  # Optimal objective is 0 again
  m.optimize()

   

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• 

  huan liu

  2021年01月21日 02:45

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  Hello,

  when I use the method of Model.getVarByName(), I have the following problems：

  subproblem1 = Model('branch1')
  model.update()    #have defined
  subproblem1 = model.copy()
  X = subproblem1.getVarByName('x_' + str(i) + '_' + str(j))  #name
  print(X)
  subproblem1.addConstr(X[index[0],index[1]] <= 0)
  
  TypeError: 'NoneType' object is not subscriptable
  
  (and the X is None)

  How can I solve this problem? Looking forward to your reply.

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