Retrieve the objective function value for multiple solutions

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Ana Guasque Ortega

2021年01月08日 13:37

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Hi,

I would like to obtain multiple feasible solutions in my model with gap = 0.1.

I have followed this post and I am able to obtain the solutions with this code:

m.setParam('PoolSearchMode',2) 
m.setParam('PoolSolutions',20) #Maximum number of solutions
m.setParam('PoolGap',0.1)

I am able to obtain the values of the variables for each solution but I also would like to know which the objective value for each solution is. Could anybody help me? This is the code for getting the solutions:

solut = m.SolCount

sol = {}

for i in range(solut):
   sol.clear()
   m.setParam('SolutionNumber', i) #

   for var in m.getVars():
         if round(var.Xn) != 0 and 'A' in var.Varname:
              sol[var.Varname] = round(var.Xn)
   print(m.objVal)   #This always prints the same objective value, I suppose this is the objective value of the optimal solution.
   print(sol)

Thanks in advance. 

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• 正式なコメント

  

  Gwyneth Butera

  • Gurobi Staff

  2021年01月08日 14:18

  Hi Ana - Please see Retrieving Solutions in the Reference Manual:

  Sub-optimal solutions can be obtained by first setting the SolutionNumber parameter and then querying the Xn attribute to obtain the solution or the PoolObjVal attribute to obtain the objective value for the corresponding solution.

  Gwyneth
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  Simranjit Kaur

  • Gurobi Staff

  2025年06月23日 03:02 編集済み

  This post is more than three years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum. Or why not try our AI Gurobot?.
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  Ana Guasque Ortega

  2021年01月11日 15:16

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  Many thanks! That was the solution. 

  Is there any way of obtaining not-repeated solutions? For example, in a classical multiple Knapsack problem, if I have 2 bins and 4 items, I'll get these solutions:

  Solution 1: 

        Bin0: item0, item2, item3

        Bin1: item 1

  Solution 2: 

        Bin0: item 1

        Bin1: item0, item2, item3

  , and they are equal. I also get other solutions, which are exactly the same, for example Solution3 = Solution 2. Is they any way of avoiding this if I don't know the actual number of solutions or should I evaluate them later?

  Thanks.

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