the time

Answered

hamzih alsmadi

• March 05, 2021 00:46
• Edited

Hello, I try to solve a problem in LP format, the problem is NP-hard. if the optimizer will find all solution should take exponential time to visit all node and compare the constraints, but when I found the solution in gurobi just it takes 5s I think should take at least 14 hours depending on the matrix, what the command line should I change to make it visit all node and take a long time

I used the parameter value is : ConcurrentMIP=1  Method=2

thank you very much.

1

• 

  Jaromił Najman

  Gurobi Staff

  • March 05, 2021 08:14

  Hi,

  Finding all solutions of a MIP problem would in general indeed take a great amount of time. However, it is possible that Gurobi is able to detect some specific structure and find solutions quickly for particular problem instances.

  I used the parameter value is : ConcurrentMIP=1 Method=2

  The parameter ConcurrentMIP is very likely not what you are looking for. For a detailed description of Gurobi's concurrent optimizer please refer to the documentation.

  The parameter Method only controls the algorithm used and not the number of desired solutions. Thus, it does not have to be set either.

  What you are looking for is Gurobi's solution pool feature, which makes Gurobi search for multiple solutions. Note that there is no way to make Gurobi search for all solutions. However, you can just set the number of desired solutions very high. A similar issue is discussed in the Community Forum post Get all solutions.

  Best regards,
  Jaromił

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