infeasible subset with Model.computeIIS()

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Emrah Öztürk

2021年03月16日 08:52

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Hi,

I have a model which according to Gurobi is infeasible. I get the following output when i use the commands model.computeIIS() and model.write('')

The variable dN_BF- is supposed to be the difference N_BF[n] - N_BF[n+1] and is not bounded. So i think this constraint should be fine.

The question I now have is why is this displayed as an infeasible subset? and what does the bound constant=1 mean?

Thanks in advance.

Emrah

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  Simranjit Kaur

  • Gurobi Staff

  2025年06月23日 02:58 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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  Matthias Miltenberger

  • Gurobi Staff

  2021年03月16日 12:12 編集済み

  Hi Emrah,

  This model is not the IIS but your original model. You need to use \(\texttt{model.write("model.ilp")}\) to write the IIS to a file - the file extension determines whether the original model or the IIS is written.

  Concerning the model itself: \(\texttt{dN_BF-[19]}\) does not appear in the \(\texttt{BOUNDS}\) section and is hence non-negative, making the model infeasible since the other two variables are fixed.

  Cheers,
  Matthias

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