Most efficient way to extract the IIS of a LP?

Awaiting user input

Haoze Wu

April 21, 2022 20:53 Edited

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Hi,

I'm trying to use the computeIIS() function from the C++ API on a LP. The documentation (https://www.gurobi.com/documentation/9.5/refman/py_model_computeiis.html) says that

"IIS results are returned in a number of attributes: IISConstr, IISLB, IISUB, IISSOS, IISQConstr, and IISGenConstr. Each indicates whether the corresponding model element is a member of the computed IIS."

However the computeIIS function does not return anything. Therefore, I'm wondering what is the most efficient way to access the constraints (constraints and bounds) in the IIS?

There seems to be two ways to access the IIS, 

1. dump it to a file;

2 or iterate over every var/constraints and check their flag. 

But I'm wondering whether there is a more efficient way?

Thanks a lot!

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• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  November 16, 2025 23:39

  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 try Gurobot, our chatbot interface offering instant, expert-level support.
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  Matthias Miltenberger

  • Gurobi Staff

  April 22, 2022 10:03

  Hi!

  What do you mean by "more efficient"? This largely depends on what you intend to do with the results. As you have mentioned, the documentation on Model.computeIIS() shows those two ways of accessing the information - either one by one or by inspecting the full IIS LP file. The method does indeed not return anything, instead it populates the respective model attributes.

  Cheers,
  Matthias

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