Unable to retrieve attribute 'x' error

回答済み

Mert Eroglu

2023年01月12日 14:19

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Hello, 

Below, you can find my code's rows.

However, i keep getting unable to retrieve 'x' error until i comment out the rows involve '.x' element.

Both x and z variables has the same range and elements of i,j,k.

Could you please help me on this, Thanks

for i in warehouse:
  for j in customers:
    for k in years:
      if z[i,j,k].x > 0.5:
        print("AAA")

関連

• Attribute

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  Jaromił Najman

  • Gurobi Staff

  2023年01月12日 15:20

  Hi Mert,

  Is a feasible solution available at the point of executing the code snippet you provided? In other words, did you run the optimize() method and Gurobi did find at least one feasible solution point before trying to access the X attribute?

  You could implement a safe guard

  if model.SolCount > 1:
    for i in warehouse:
      for j in customers:
        for k in years:
          if z[i,j,k].x > 0.5:
            print("AAA")
  else:
    print("No feasible solution available")

  If the above does not help, please provide a minimal reproducible example resulting in the error.

  Best regards, 
  Jaromił

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  Mert Eroglu

  2023年01月13日 06:56

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  Hello, thanks for your fast support. I implemented your codes into mine and printed:  "No feasible solution available". Therefore why .x is not being used in my code, result i didn't understand that part. You can find a part of example below.

  I have more constraints, but the outcome is infeasible despite commenting out my constraints.

  When i run with constraints, my code gives an error at the first line with ".x".

  Thanks.

   

  x = {}
  for i in warehouses:
      for j in customers:
          for k in years:
              x[i,j,k] = m.addVar(vtype=GRB.BINARY, name="x_%d_%d_%d" % (i, j,k))

   

  z = {}
  for i in warehouses:
      for j in customers:
          for k in years:
              z[i,j,k] = m.addVar(vtype=GRB.BINARY, name="z_%d_%d_%d" % (i,j,k))

   

  for i in warehouses:

    for j in customers:
           for k in years:
                if z[i,j,k].x > 0.5:
                    print("Customer", j, "will be switched in year",k)

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  Jaromił Najman

  • Gurobi Staff

  2023年01月13日 08:14

  I have more constraints, but the outcome is infeasible despite commenting out my constraints.

  In this case, please refer to the Knowledge Base article How do I determine why my model is infeasible?

  When i run with constraints, my code gives an error at the first line with ".x".

  Just to make sure, do you call optimize() before trying to access the X attribute? It is not present in your code snippet.

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  Mert Eroglu

  2023年01月16日 11:26

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  I was getting the error despite calling optimize(), i guess there was a problem with my constraints. But i used another approach for my problem, for now.

  Thanks for your support.

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