Can model.copy() also copy my own data structures of variables in the original model (in Python)?

回答済み

Bo Lan

2019年09月20日 17:42

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Greetings,

I made a model and added binary decision variables  into a data structure like the following in Python:

def make_model(some_arguments):

      model = grb.Model()

      ......

      x[i,j] = model.addVar(......)

      y[i,j] = model.addVar(......)

      ......

      model._data = x, y

      return model

 

Then in another function I can extract those groups of variables, i.e. x, y, like

def solve_model(model):

      x, y = model._data

      ......

 

Now I want to make a copy of the original model and manipulate the copy and solve it again. the code is something like

copy = model.copy()

This is a good copy of the original  model but it does not copy my data structure of x, y. When I call the following function

def solve_copy(copy):

      x, y = copy._data

     for i in y:
          y[i].ub = 0

      ......

The line of 'x, y = copy._data' will throw an error of 'AttributeError: 'gurobipy.Model' object has no attribute '_data''. then I cannot manipulate y with their upper bounds.

 

Can anyone give me some suggestions about how to copy a model and its data structures of decision variables  simultaneously?

 

Thanks,

 

Larry

 

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  Simranjit Kaur

  • Gurobi Staff

  2024年12月06日 00:53

  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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  Baptiste Lambin

  2020年01月10日 14:42

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  Hello there,

  I don't know the policy of this forum regarding duplicate posts.

  To avoid posting the same topic, I thus post here to see if anyone has an answer to this, as I also would like to be able to copy a model together with its custom attributes (attributes starting with _)

  Thanks a lot,
  Regards,
  Baptiste

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  Matthias Miltenberger

  • Gurobi Staff

  2020年01月15日 16:27

  Hi Larry and Baptiste,

  I don't suppose there is a way currently to copy user data when calling Model.copy(). I recommend to only use one data object _data to store all your user data and after copying the model call model2._data = model._data.

  Cheers,
  Matthias

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  Baptiste Lambin

  2020年01月15日 16:45

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  Hi Matthias,

  Thanks for your answer.

  However for the case described here, using model2._data = model._data will not work, as model._data contains variables from model, model2._data would also contain the variables from model. Here is a minimal working example in Python :

  m = Model()
  x = m.addVar(vtype=GRB.BINARY, name="x")
  y = m.addVar(vtype=GRB.BINARY, name="y")
  m.update()
  m._data = [x,y]
  m2 = m.copy()
  m2._data = m._data
  x2,y2 = m2._data
  m2.addConstr(x2 + y2 == 1)

  The addConstr call then throw an error "GurobiError: Variable not in model".
  I am not surprised by this though, but it would be nice to be able to make it work "easily".
  Of course, you can always create the correct m2._data using
  m2._data = [m2.getVarByName("x"), m2.getVarByName("y")]
  but it is a bit cumbersome.

  The usecase I was thinking about is e.g. callbacks, where using custom attributes makes it really easy to access the variables inside the callback. Having the correct variables directly in m2._data make it easier to use e.g. two different callbacks.

  But I'll use getVarByName to get it done, the current behavior makes sense in a way, I was just wondering if there was some obscure way to easily do this.

  Thanks again,
  Regards,
  Baptiste

   

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  Bo Lan

  2020年01月15日 20:56

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  Thank you, Baptiste, for sharing your practice. It's helpful.

  Larry

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