Get all solutions

Answered

Maxim Santalov

• August 28, 2020 08:34

How I can get all solutions of the model, if the SolutionNumber is >1?

0

• Official comment

  

  Matthias Miltenberger

  Gurobi Staff

  • August 28, 2020 09:29
  • Edited

  Hi Maxim,

  Did you already check out this guide on SolutionPools?
  This post about how to save solutions directly to disk as they are found using the SolFiles parameter might also be interesting.

  Cheers,
  Matthias
• 

  Maxim Santalov

  • August 28, 2020 09:57

  

  

  

  Thank you for your reply.

   

  I am new to Gurobi and some solutions presented at guide are not obvious for me.

  By this moment, my code looks like this:

  ....(Model initialization, setting up Vars and Cons)...

  m.setParam(GRB.Param.PoolSearchMode, 2)

  m.optimize()

  nSolutions = m.SolCount
  print('Number of solutions found: ' + str(nSolutions))
  for sol in range(nSolutions):
      m.setParam(GRB.Param.SolutionNumber, sol)
      print(m.ObjVal)
      for station_idx in range(0, len(station_in_route)):
  
          m.cbGetSolution(m.getVars())

         ### Here I need to request the current solution from the model

         # If variable in solution is  > 0:
                 # print(' Station %d' % station_idx, end='\n')
  print('')

  If you could help with editing part of the code marked as(###) I will be very glad.

  WIth kind regards,

  Maxim

   

  0
• 

  Matthias Miltenberger

  Gurobi Staff

  • August 31, 2020 10:46

  Hi Maxim,

  To query the n'th solution value of a variable you need to query the Xn attribute of that variable after setting the SolutionNumber to the respective number n. The method cbGetSolution is only used to work with a solution while running inside a callback. You don't seem to be using callbacks in your code.

  Cheers,
  Matthias

  1
• 

  Maxim Santalov

  • September 01, 2020 06:33

  

  

  

  Hi Matthias,

  Thank you for the reply. It helped to restore order in my code.

  I will leave it here( possibly, it would help someone):.

  ...(previous part remains the same)
  for sol in range(nSolutions):
      m.setParam(GRB.Param.SolutionNumber, sol)
      values = m.Xn
  ...I receive a list of values of the solution with specified SolNumber

  0

Please sign in to leave a comment.