Slow moving BestBd and Gap

ユーザーの入力を待っています。

songtao wang

2023年02月15日 12:36

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I have a question about the log of the gurobi returns. As I know that the head of the log will be like the following picture.

and when I was programming, I found that the BestBd data don't change. But I get some knowledge form website that the normal progress will be like the Incumbent will decrease and the BestBd will increase until the Gap between them is small enough. The optimization problem will be solved. The following picture shows the message of the log of my programming.

So I want to know the reason of this problem.

and then I also want to decrease the Gap to obtain a better solution. But now the BestBd is unchanging and the Gap is also big for me. So I hope that you can tell me the way the decrease the Gap.

The code is more than 150 rows, so I will show the main part of it as follow. If you need more information about my program, I will send it in time.

Hoping to get your instructions sincerely, Thank you.

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  Jaromił Najman

  • Gurobi Staff

  2023年02月15日 13:29

  Please note that posting screenshots of your code is of no help because it is not copy-pastable.

  You could generate an LP file of your model via the gurobi_write() function and share it with the community. Maybe, then someone can provide help. Note that uploading files in the Community Forum is not possible but we discuss an alternative in Posting to the Community Forum.

  But I get some knowledge form website that the normal progress will be like the Incumbent will decrease and the BestBd will increase until the Gap between them is small enough. The optimization problem will be solved.

  While this is true for most problems, there are models that behave completely different. Especially purely discrete models often show a slowly (or even almost non-moving) bounds. This can be a formulation issue. The webinar about converting weak formulations to strong ones for MIPs might be of interest to you.

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