Print entire solution in VRP callback

[Thomas Bridi]

Hello,

I'm trying to print each solution that the solver finds in a VRP.

In this group I've found the solution callback:

class SolutionCallback(object):

        def __init__(self, model):

            self.model = model

        def __call__(self):

            print("Solution", self.model.CostVar().Max())

            

solution_callback = SolutionCallback(routing)

routing.AddAtSolutionCallback(solution_callback)

And I have the classical print_solution of the examples:

def print_solution(manager, routing, assignment):

    """Prints assignment on console."""

    print('Objective: {} miles'.format(assignment.ObjectiveValue()))

    index = routing.Start(0)

    plan_output = 'Route for vehicle 0:\n'

    route_distance = 0

    while not routing.IsEnd(index):

        plan_output += ' {} ->'.format(manager.IndexToNode(index))

        previous_index = index

        index = assignment.Value(routing.NextVar(index))

        route_distance += routing.GetArcCostForVehicle(previous_index, index, 0)

    plan_output += ' {}\n'.format(manager.IndexToNode(index))

    print(plan_output)

    plan_output += 'Route distance: {}miles\n'.format(route_distance)

What I would like is to call the print_solution function from the __call__ of the SolutionCallback class.

What I can not find is the assignment. 

How can I get the assignment in the solution in the callback?

Thanks,

Thomas

[Vincent Furnon]

You actually don't need the assignment, you can directly look at the variable values when the callback is called. For instance, instead of index = assignment.Value(routing.NextVar(index)), just do index = routing.NextVar(index).Value().

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[Thomas Bridi]

It worked. Thanks

Il giorno lunedì 20 gennaio 2020 16:08:39 UTC+1, Vincent Furnon ha scritto:

You actually don't need the assignment, you can directly look at the variable values when the callback is called. For instance, instead of index = assignment.Value(routing.NextVar(index)), just do index = routing.NextVar(index).Value().

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[Haakon HR]

Is there a way to access the CumulVars inside the callback? I'm struggling with it at the moment. I'm using something like the below, but it does not work currently

class SolutionCallback(object):

        def __init__(self, model):

            self.model = model

            self.time = model.GetDimensionOrDie("Time")

        def __call__(self):

           index = self.model.NextVar(0)

           time_var = self.time.CumulVar(index)

           print(time_var.Value())

On Monday, January 20, 2020 at 4:08:39 PM UTC+1, Vincent Furnon wrote:

You actually don't need the assignment, you can directly look at the variable values when the callback is called. For instance, instead of index = assignment.Value(routing.NextVar(index)), just do index = routing.NextVar(index).Value().

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[Haakon HR]

The reason was obvious the moment I clicked "reply". I guess it is just due to the fact that the variable doesn't actually have a value, but an interval so only Min() and Max() makes sense; not Value().