attribute error '__cindex__' using absolute value and square root

回答済み

María Ciudad Alañón

2022年06月08日 10:34

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Hello!

I'm trying to implement a maximization of the following function: \sqrt(\abs(I)) + \sqrt(\abs(J)), where I and J are linear combinations of other variables. For that, I have add auxiliary variables for I and J and then I add also auxiliary variables for the absolute value (Iabs and Jabs) and for the square root of them (Isqrt and Jsqrt) and add the correspond constraints as follows:

m.addGenConstrAbs(Iabs,I)
m.addGenConstrAbs(Jabs,J)
m.addGenConstrPow(Iabs,Isqrt,0.5)
m.addGenConstrPow(Jabs,Jsqrt,0.5)

However I got the following error: AttributeError: 'gurobipy.LinExpr' object has no attribute '__cindex__'

Do you know what am I doing wrong? Thank you!

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• 正式なコメント

  

  Simranjit Kaur

  • Gurobi Staff

  2025年11月16日 23:35

  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 try Gurobot, our chatbot interface offering instant, expert-level support.
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  Marika Karbstein

  • Gurobi Staff

  2022年06月08日 13:28 編集済み

  Hi María,

  How did you add your auxiliary variables?
  Doing like this

  import gurobipy as gp
  m = gp.Model("abs")
  
  x = m.addVars(5, vtype = gp.GRB.CONTINUOUS, name = "x")
  Iabs = m.addVar(vtype = gp.GRB.CONTINUOUS, lb = 0, name = "Iabs")
  I = gp.quicksum(x[i] for i in range(4))
  m.addGenConstrAbs(Iabs, I, "abs")

  would result in the error you mentioned.

  You need to add the auxiliary variable and the constraint also to the model:

  import gurobipy as gp
  m = gp.Model("abs")
  
  x = m.addVars(5, vtype = gp.GRB.CONTINUOUS, name = "x")
  Iabs = m.addVar(vtype = gp.GRB.CONTINUOUS, lb = 0, name = "y")
  I = m.addVar(vtype = gp.GRB.CONTINUOUS, name = "I")
  m.addConstr(I == gp.quicksum(x[i] for i in range(4)))
  m.addGenConstrAbs(Iabs, I, "abs")

  I hope this helps,
  Marika

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  María Ciudad Alañón

  2022年06月08日 14:21

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  Thank you very much! It has been very helpful!

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