KeyError: addConstr

Answered

Krypt

November 24, 2022 07:19 Edited

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Hello,

I am encountering keyError at the constraint highlighted in bold. The reproducible code is below. I want to have a set of constraints where my binary variables X are summed up to L[i]. I want to sum over X[i,j] for all i in pot_route and for all j in route_set only, when j meets certain conditions.

My constraints should look like:

L[12] = X[2_OD1,124] + X[2_OD1,1234] + 

L[13] = X[2_OD1,134]

L[24] = X[2_OD1,124] + X[10_OD2, 24]

L[23] = X[2_OD1,1234] + X[10_OD2, 234]

L[34] = X[2_OD1,134] + X[2_OD1,1234] + X[10_OD2, 234]

However, I get a keyError when I use this code. Any help is much appreciated!

pot_route = {'2_OD1': [124, 1234, 134], '10_OD2': [24, 234]}
which_links_in_route = {134: [13, 34], 234: [23, 34], 1234: [12, 23, 34], 24: [24], 124: [12, 24]}
road_travel_time = {12: 4.5, 13: 5, 24: 6, 23: 0.8, 34: 5}
mdl = Model('OTR')
X = {}
z1 = {}
z2 = {}
for item in pot_route:
   for element in pot_route[item]:
       X[item,element] = mdl.addVar(vtype=GRB.BINARY, name="X[{0},{1}]".format(item,element))
mdl.addConstrs((quicksum(X[item,j] for j in pot_route[item])==1) for item in pot_route)
LC = {}
for item in road_travel_time:
    route_set = []
    for element in which_links_in_route:
        if item in which_links_in_route[element]:
            route_set.append(element)
    mdl.addConstr(LC[item]==quicksum(X[i,j] for i in pot_route for j in route_set), LC)

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  Jaromił Najman

  • Gurobi Staff

  November 24, 2022 11:34 Edited

  Hi Tanvir,

  The error you get occurs because you have to introduce \(\texttt{LC[item]}\) as an optimization variable first.

  for item in road_travel_time:
      route_set = []
      for element in which_links_in_route:
          if item in which_links_in_route[element]:
              route_set.append(element)
      LC[item] = mdl.addVar(lb=-GRB.INFINITY, name="LC[{0}]".format(item))
      mdl.addConstr(LC[item]==quicksum(X[i,j] for i in pot_route for j in route_set), name="L[{0}]".format(item))

  However, this results in another key error which is caused by how you construct your \(\texttt{route_set}\).

  KeyError: ('10_OD2', 1234)

  This means, that you try to access \(\texttt{X['10_OD2', 1234]}\) which is not defined. I don't know what you are trying to achieve with the \(\texttt{route_set}\) so I will leave this fix up to you. Maybe the following is already enough

  dl.addConstr(LC[item]==quicksum(X[i,j] for i in pot_route for j in route_set if j in pot_route[i]), name="L[{0}]".format(item))

  Best regards, 
  Jaromił

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