Modelling Nonlinear Objective function/Constraint

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Suyog Nigudkar

2021年12月22日 12:25 編集済み

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Dear all,

I am facing issue in modelling a nonlinear constraint in Gurobi : x^3 >= k; (where x is the a variable between [-1,1] and k is a constant)

I am modelling the constraint as shown below:

int b = 3;
model.addGenConstrPow(x, z, b);

model.addConstr(z >= k);

I am facing the following error:

Error code = 10003
lower bound of x variable is less than zero for POW function

Can someone explain how to manage the issue as I cannot change the bounds on the variable to positive values?

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• 正式なコメント

  

  Simranjit Kaur

  • Gurobi Staff

  2025年06月23日 02:42 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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  Jaromił Najman

  • Gurobi Staff

  2021年12月22日 12:37 編集済み

  Dear Suyog,

  The documentation of the addGenConstrPow method explicitly states that the lower bound of the \(x\) variable has to be nonnegative. This is mainly to avoid domain error caused when non-integer values are used in the exponent.

  To model \(x^3\) with \(x \in [-1,1]\), you can use the addGenConstrPoly method. Your constraint can be model as

  import gurobipy as gp 
  from gurobipy import GRB
  
  m = gp.Model("test")
  
  x = m.addVar(lb=-1, ub=1, vtype=GRB.CONTINUOUS, name="x")
  z = m.addVar(lb=-1, ub=1, vtype=GRB.CONTINUOUS, name="z")
  
  # z = 1.0 * x^3 constraint
  m.addGenConstrPoly(x, z, [1,0,0,0])

  Best regards,
  Jaromił

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  Suyog Nigudkar

  2021年12月22日 12:40

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  Thanks a lot Jaromil. 

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