Is it possible to dump the discovered implied bounds after solving LP?

Answered

Haoze Wu

• January 26, 2021 22:31
• Edited

I'm not sure whether this is a sensible question. If some bound tightening/propagation techniques are used when solving a LP problem (e.g., examining a row when revised Simplex is running), is it possible to extract those updated bounds?

For example, 

If the original query is
x1<=4 and x2 >= 2 and x1 + x2 <= 3

I presume the simplex engine can deduce that x1 has a tighter upper bound of 1. My question is whether I can extract that tighter bound? 

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• Official comment

  

  Simranjit Kaur

  Gurobi Staff

  • December 06, 2024 00:36

  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?.
• 

  Jaromił Najman

  Gurobi Staff

  • January 27, 2021 11:38
  • Edited

  Hi,

  You cannot access the variable bounds deduced by a specific heuristic. However, you can access the presolved model which will most likely hold the information you seek. The Knowledge Base article How does presolve work? may be of interest. Note that, if a problem is too simple, then the presolve procedure will most likely solve the problem completely, meaning that the resulting presolved model is empty.

  Best regards,
  Jaromił

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• 

  Haoze Wu

  • January 27, 2021 16:51

  

  

  

  Ah I see. Thanks for the explanation!

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