gurobipy.GurobiError: Second tuple member should be a Var

Ongoing

SAMAN ESKANDARZADEH

• June 25, 2021 01:51

Hello,

I have a constraint as follows that produces error "gurobipy.GurobiError: Second tuple member should be a Var". I do not know how to resolve this.

model.addConstrs(y[j]-y[i] <= (1 - x.sum(i, '*')) for (i, j) in index_pairs)

  The full error message is as follows:

ERROR:root:Traceback (most recent call last):
File "/DataWarehouse/BreakPolicyComparisonProject/MutipleVehicle/main.py", line 111, in pricing_mip
planning_quantities, dic_distance_matrix, service_time_task, CAPACITY,dual_values)
File "\DataWarehouse\BreakPolicyComparisonProject\MutipleVehicle\sample_models.py", line 163, in generate_pricing_mip_model
1 - var_consecutive_visits_pairs.sum(i, '*')) for (i, j) in index_pairs)
File "src\gurobipy\model.pxi", line 3443, in gurobipy.Model.addConstrs
File "\DataWarehouse\BreakPolicyComparisonProject\MutipleVehicle\sample_models.py", line 163, in <genexpr>
1 - var_consecutive_visits_pairs.sum(i, '*')) for (i, j) in index_pairs)
File "src\gurobipy\linexpr.pxi", line 483, in gurobipy.LinExpr.__mul__
File "src\gurobipy\quadexpr.pxi", line 45, in gurobipy.QuadExpr.__init__
File "src\gurobipy\linexpr.pxi", line 47, in gurobipy.LinExpr.__init__
gurobipy.GurobiError: Second tuple member should be a Var

 

0

• 

  Jaromił Najman

  Gurobi Staff

  • June 25, 2021 07:34
  • Edited

  Hi,

  Could you provide a minimal reproducible example showing this issue?

  Best regards,
  Jaromił

  0
• 

  SAMAN ESKANDARZADEH

  • June 25, 2021 08:10

  

  

  

  Thanks. I found out what the problem was. I had simplified my question but it turned out that the source of the error was in the parts, I had excluded. 

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• 

  Shashank Vats

  • September 16, 2021 12:37

  

  

  

  Hey SAMAN ESKANDARZADEH,

  I'm facing the same issue while using LinExp(). Can you please let me know how you solved this issue? 

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• 

  SAMAN ESKANDARZADEH

  • September 16, 2021 13:10

  

  

  

  Hey Shashank,

  It was a while ago, I do not recall it exactly, however, I think the problem was that for some (i,j) in the index_pair, there was not a corresponding variable defined. So for example tuple (2,3) was in index_pairs but x[2,3] was not defined as a var. I hope this helps.   

   

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• 

  Shashank Vats

  • September 17, 2021 06:15

  

  

  

  Hi SAMAN ESKANDARZADEH,

  Thanks for the reply!

  In my case, I'm using the following statement:

  objective_func = LinExpr((dict1_ijk.get((i, j, k), 0) *
                                      dict2.get((d, l),0), dict3_dijl.get((d, i, j, l),0))
                                      
                                     for d in list1 for j, k, l in list2 
                                     for i in dict4_j[j] )
  
  

  In the code snippet above, the second element of the LinExp() function, dict3_dijl.get((d, i, j, l),0), should be Var type but since I'm using get() function to check if that variable is present or not and returning 0 if its not, I'm being thrown with the error telling the second tuple member should be Var (the get() function is returning 0 when the variable is not present).

  Can you suggest a way to get past this error? 

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