Subtour Elimination for several vehicles (VRP)

   Hi,

I try to implement the Subtour Elimination constraint for a Vehice Routing Problem with the "callback methode".
I tried to modify the code from tsp.py so it would work with several vehicles (highlited in bold). My variables consist of three indices (i,j for the nodes, k for the vehicle), so i added k's where I thought it would be necessary. Additionally, I added a second argument in the subtour-function (motivation: for every vehicle k the function looks for subtours seperately) and implemented a for-loop in the subtourelim function to eliminate subtours for every vehicle k.
Nevertheless, I still get a solution with subtours if I use more than just one vehicle. Following the code for the functions subtourelim and subtour.

 def subtourelim(model, where):
     for k in SetK: #SetK=[k for k in range(K)], where K is the maximal number of vehicles used
         if where == GRB.Callback.MIPSOL:
             vals = model.cbGetSolution(model._vars)
             # find the shortest cycle in the selected edge list
             tour = subtour(vals,k)
             if len(tour) < I: # I is the number of nodes to be visited
                 # add subtour elimination constr. for every pair of cities in tour
                 model.cbLazy(gp.quicksum(model._vars[i, j, k] for i, j in combinations(tour, 2))
                              <= len(tour)-1)
                
 def subtour(vals,k):
     # make a list of edges selected in the solution
         
     edges = gp.tuplelist((i, j,k) for i, j, k in vals.keys() if vals[i, j, k] > 0.5)
     unvisited = list(i for i in SetI if selection[i]==1)
     cycle = range(num_I+1)  # initial length has 1 more city
     while unvisited:  # true if list is non-empty
         thiscycle = []
         neighbors = unvisited
         while neighbors:
             current = neighbors[0]
             thiscycle.append(current)
             unvisited.remove(current)
             neighbors = [j for i, j, k in edges.select(current, '*') if j in unvisited]
         if len(cycle) > len(thiscycle):
             cycle = thiscycle
     return cycle