Unexpectedly many solutions from Solution Pool

Answered

Alejandro Schaffer

• July 21, 2023 01:57

We are using Gurobi 10.0.0 and gurobipy

We use 

num_sol = 5

model.setParam(GRB.param.PoolSearchMode, 2)
model.setParam(GRB.param.PoolSolutions, num_sol)

On some instances get 15 (not necessarily distinct) solutions even though the value of num_sol is set to a constant that is < 15. From other posts, I understand why we get the same solution multiple times, but I do not understand why we get more than num_sol solutions.

Has anyone observed this behavior?

Alejandro Schaffer

Are 

Related to

• Solution Pools

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• 

  Marika Karbstein

  Gurobi Staff

  • July 21, 2023 10:55

  Hi Alejandro,

  Do I understand correctly that after optimization if you check the attribute model.SolCount you get 15 but calling model.getParamInfo('PoolSolutions')  gives
  ('PoolSolutions', <class 'int'>, 5, 1, 2000000000, 10) ?

  Can you share an example?

  Thanks, Marika

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• 

  Marika Karbstein

  Gurobi Staff

  • July 21, 2023 13:09

  The problem was solved

  • use model.SolCount  to get the number of stored solutions
  • use parameter SolutionNumber to define which solution to access when querying attribute Xn, ObjNVal, or PoolObjVal  

  An example can be found in poolsearch.py

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