set the value of unused variables

Answered

Amir Ghiasi Noughaby

May 10, 2021 06:26

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Hi, 

In my model, there are some unused binary variables. I want to set the default value of them zero rather than one. How can I do this?

 

Thanks  

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• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  June 23, 2025 02:55 Edited

  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

  May 10, 2021 08:13

  Hi,

  In Gurobi, variables don't have a default value. If there are multiple optimal solutions (for example by choosing different values for variables that do not participate in any constraint or the objective), Gurobi will return the first one it finds -- which one this is may depend on the solver path.

  If you want "unused variables" to be zero, you could simply add a constraint that fixes them to zero or you could add them to your objective function with the appropriate sign (depending on whether you're maximizing or minimizing).

  Silke

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