Maximum of two values

Answered

SAKIR KARAKAYA

March 03, 2023 06:33 Edited

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Hi.

In my model coded in Python, after getting the optimal values of some variables, I built a mathematical expression to get a number, i.e. 

for i in I:
    y[i] = max(0, y[i-1]+ a*z[i-1])

Here z[i-1] and and y[i-1] are variables' optimal values obtained by solving an optimization model. I'm trying to make y[i] equal to zero if the second expression within the paranthesis takes a negative value.

However, I am getting a "NotImplementedError" error code due to the "max" operation.

Could you kindly help me to solve this problem? Thank you in advance.

Sakir.

 

 

s

Related to

• General Constraints
• Python

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  Jonasz Staszek

  • Community Moderator

  March 03, 2023 07:44

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  Hi Sakir,

  first of all, the max_() method in Guroby Python has a slightly different syntax - take a look at the documentation.

  On top of this, the max_() method takes variables as arguments and not linear expressions. You might want to try something along the lines of:

  aux = model.addVars(I, vtype="C", name="aux")
  for i in I
      model.addLConstr(aux[i] == y[i-1] + a*z[i-1])
      model.addConstr(y[i] == max_(aux[i], constant=0))

  Hope this helps.

  Best regards
  Jonasz

   

   

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  Gwyneth Butera

  • Gurobi Staff

  March 03, 2023 13:56 Edited

  Also, the article How do I model logical and general expressions? may be of use when using max in a constraint in gurobipy.

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  SAKIR KARAKAYA

  March 03, 2023 19:28 Edited

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  Hi,

  Thank you so much for your quick response. The equation I shared is not a constraint. After solving the constrained optimization model, I'd like to make a straightforward mathematical operation. Actually, when I tried the following, the problem is solved. 

  y[i] = max(0, y[i-1].X+ a*z[i-1].X)

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