Retrieving multiple solutions using Pyomo

Answered

Federico D'Onofrio

June 28, 2023 10:15 Edited

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Hi!

I am using Pyomo and I want to retrieve the solutions from the SolutionPool that Gurobi found. I know how to do it with Gurobi's Python API, but I am struggling to do the same when using Pyomo.

Thanks,

Federico

Related to

• Pyomo
• Solution Pools

0

• 

  Lennart Lahrs

  • Gurobi Staff

  June 28, 2023 15:36

  Hi Frederico,

  Please find below a suggestion of how to access objective values and the Xn attribute of Gurobi model variables for multiple solutions in Pyomo.

  import pyomo.environ as pe
  
  m = pe.ConcreteModel()
  ...
  opt = pe.SolverFactory('gurobi_persistent')
  opt.set_instance(m)
  opt.set_gurobi_param("PoolSolutions", 2)
  opt.set_gurobi_param("PoolSearchMode", 2)
  opt.solve()
  
  # Print number of solutions stored
  nSolutions = opt.get_model_attr("SolCount")
  print('Number of solutions found: ' + str(nSolutions))
  
  # Print objective values of solutions
  for e in range(nSolutions):
      opt.set_gurobi_param("SolutionNumber", e)
      print('%g ' % opt.get_model_attr("PoolObjVal"), end='')
  print('')
  
  # Print variable values of different solutions
  opt.set_gurobi_param("SolutionNumber", 0)
  opt._solver_model.printAttr('Xn')
  opt.set_gurobi_param("SolutionNumber", 1)
  opt._solver_model.printAttr('Xn')

  Did this do the trick for you?
  
  Best regards,
  Lennart

  0

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