Using "addGenConstrPow" but model is infeasible

回答済み

Jack Kaz

2022年11月17日 11:06 編集済み

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Hello together,

I am trying to solve an easy power function for "x = 20 + A"  with A=200, but it is infeasible. I do not understand why. If I set my variable A = 0 it is feasible. Thank you.

Here is my example:

model = gp.Model("test")

A = 200

x0 = model.addVar(vtype=GRB.CONTINUOUS, name="x0")
x = model.addVar(vtype=GRB.CONTINUOUS, name="x")
x_pow4 = model.addVar(vtype=GRB.CONTINUOUS, name="x_pow4")

model.addConstr(x0 == 20)
model.addConstr(x == x0 + A)

model.addGenConstrPow(x,x_pow4,4)

model.optimize()

関連

• Numerics
• General Constraints

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• 正式なコメント

  

  Simranjit Kaur

  • Gurobi Staff

  2026年11月13日 01:52

  This post is more than two 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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  Jaromił Najman

  • Gurobi Staff

  2022年11月17日 11:42

  Hi Jack,

  The issue is caused by the default value of the FuncMaxVal parameter which is 1e+6. This limits the bounds on variables participating in general constraints, but \(220^4 > 10^6\). Thus, your model is declared as infeasible.

  To avoid this, you have to set the parameter to a larger value, e.g.,

  model.setParam("FuncMaxVal",10e+20)

  Please note that working with such large values is not recommended. So, if you want to extend your model and indeed work with the value of \(\texttt{x_pow4}\) in an extension of your model, then this might very likely lead to numerical issues.

  Best regards, 
  Jaromił

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  Jack Kaz

  2022年11月17日 12:34

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  Hi Jaromil,

  thank you very much for your advice!

  Unfortunately, we have this big values in thermodynamics when working with absolute temperatures.. Is there a suggestion to reduce the possibility of numerical issues? I was thinking of a way to limit the value range of the function.. or is it done when defining upper and lower bounds to the variables?

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  Jaromił Najman

  • Gurobi Staff

  2022年11月17日 13:42

  Hi Jack,

  Unfortunately, we have this big values in thermodynamics when working with absolute temperatures.. Is there a suggestion to reduce the possibility of numerical issues? I was thinking of a way to limit the value range of the function.. or is it done when defining upper and lower bounds to the variables?

  I understand. You could re-scale the orders of magnitude, e.g., say that 1 unit for some variable equals 1000 degrees instead of 1. This would already scale the values by 4 orders of magnitude. For more detailed tips, please have a look at our Guidelines for Numerical Issues.

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