Lazy cuts clarification

Answered

Matteo Petris

November 20, 2020 10:00

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I have a question regarding the lazy constraints.

From the reference manual, in addLazy, it seems to me that the lazy constraints included at a B&B node are not globally valid, but they are valid only in the subtree with root at that node.

I say this because of the following sentence: "Node solutions will usually respect previously added lazy constraints, but not always."

However, from the following post, I understand that they should be globally valid.

https://support.gurobi.com/hc/en-us/articles/360013197472-Can-I-add-locally-valid-constraints-in-Gurobi-MIP-

Can you please clarify this point?

Thanks a lot

 

 

 

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• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  June 23, 2025 03:04 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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  Jaromił Najman

  • Gurobi Staff

  December 01, 2020 12:20

  Hi Matteo,

  The sentence "Node solutions will usually respect previously added lazy constraints, but not always." means that during an optimization run with multiple threads, one thread may find a solution which results in the addition of some lazy constraint, while a different thread already computed some lower bound for a particular node without this lazy constraint. In the output, it then might occur that the LP relaxation solution of a node in such a case may not respect the added lazy constraint. However, all subsequent nodes will respect the newly added lazy constraint.

  Best regards,
  Jaromił

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