VRP Column generation

[Thomas 1234]

Hello,

is it possible to access the created routes while solving the VRP somehow?

I would like to create a list of every route generated by the algorithm while solving the problem.

Thank you in advance.

[Laurent Perron]

There are no column generation techniques in the solver.

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

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[Thomas 1234]

okay thanks.

 but the solver has to generate tours somehow? can I get them?

[Laurent Perron]

The solver computes a solution, not individual tours. When it finds them, it reports them in a solution.

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

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[Vincent Furnon]

You can get solutions during the search using the RoutingModel::AddAtSolutionCallback(callback) method which sets the solver to call 'callback' each time a new solution is found. In the context of the callback all variables will be set, so you can get individual tours by iterating on each vehicle, getting its start node, then iterating on its route by getting the value of Next variables until you reach the vehicle's end node (a bit like you would to do to display a solution).

Vincent

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[Thomas 1234]

Tank you,

I think that is what I looked for.

[th.b...@gmail.com]

I tried to write a callback that iterates trough the tours but somehow it cant get the next nodes. I think the problem ist the red marked part.

 

class solution_found(object):

        def __init__(self, model):

            self.model = model

            self.routing = routing

            self.manager = manager

 

        def __call__(self):

            print(self.model.CostVar().Min())

 

            tours = []

            for vehicle_id in range(data['num_vehicles']):

                t = []

                print(vehicle_id)

                index = self.routing.Start(vehicle_id) #get first node

 

                while not self.routing.IsEnd(index): #append node if not end

                    node_index = self.manager.IndexToNode(index)

                    print(node_index)

                    t.append(node_index)

 

                    index = self.routing.NextVar(index) #get next node

                    print(t)

 

            t.append(self.manager.IndexToNode(index)) #append last node

            tours.append(t) #append tour to list of tours

            print(tours)

 

 

    solution_callback = solution_found(routing)

    routing.AddAtSolutionCallback(solution_callback)

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[Vincent Furnon]

It should be: index = self.routing.NextVar(index).Value() #get next node

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