How to use multiplication of variable inside gp.max_() ?

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Md Yeakub Hassan

2020年10月12日 16:21

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x is a continuous varibale, and a[] is an array of decision variables.  I want to add the following

model.addConstr(x == gp.max_(a[0]*1, a[1]*3, a[2]*4))

But I am getting error. How to solve this?

 

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  Simranjit Kaur

  • Gurobi Staff

  2025年06月23日 03:06 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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  Silke Horn

  • Gurobi Staff

  2020年10月13日 09:38

  The max_ function only takes a list of decision variables (or constants). You will have to define some auxiliary variables (say aux[1] and aux[2]) and add constraints as follows:

  model.addConstr(aux[1] == a[1]*3)
  model.addConstr(aux[2] == a[2]*4)

  Then you can add the max constraint using the auxiliary variables:

  model.addConstr(x == gp.max_(a[0], aux[1], aux[2]))

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  Alexia Payan

  2021年05月21日 22:21

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  Hello Silke,

  I have a question regarding the use of the max_ function. I noticed that using it slows down the optimization somewhat. Is this because it is technically not a linear constraint? Have you ever observed a similar behavior?

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  Alison Cozad

  • Gurobi Staff

  2021年06月14日 14:45

  Yes, adding the max_() constraints may make your model harder to solve.  Depending on how \(x\) is used in your model, the max_() general constraint helper function will add either constraints or constraints and variables to your model.  Please check out Part 2 of this Modeling presentation from when the general constraint helper functions were first introduced to get a feel for how this is done.

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