Model

Here is a brief description of the modeling of the problem in this simulation framework.

---

Locations

The default Location class is used.

for location_id, location_data in probdata['locations'].items():
    location = Location( location_id )
    location.x = location_data['x']
    location.y = location_data['y']
    model.add_location( location )

---

Orders

The default Order class is used.

• An order provider is used to request the orders.

orders = []

for order_id, order_data in probdata['orders'].items():
    order = Order( order_data['id'] )
    order.release_date = order_data['release_date']
    order.pickup_location = model.get_location_by_id( order_data['pickup_location'] )
    order.delivery_location = model.get_location_by_id( order_data['delivery_location'] )
    order.earliest_delivery_start = order_data['earliest_delivery_arrival']
    order.latest_delivery_start = order_data['latest_delivery_arrival']    
    orders.append( order )

model.env.process( order_provider( model, orders, decision_point_on_request= False ) )

---

Vehicles

A custom vehicle class (SDDPVehicle) is used.

• The distance callback (travel_distance) and the travel times callback (travel_time) return the (vehicle-independent) distance and travel time, respectively, between the given locations.

Vehicle classTravel time and distance

class SDDPVehicle(Vehicle):
    def __init__( self, id:str ) -> None:
        super().__init__(id)

def travel_distance( self, origin:Location, destination:Location ):
    """
    "(...) we first calculate the Manhattan distance between locations (...)"
    """
    return manhattan_distance( origin.x, origin.y, destination.x, destination.y )

def travel_time( self, origin:Location, destination:Location ):
    return round( 60 * self.travel_distance( origin, destination ) / self.aux['speed'] )

• Initial location and speed are set for each vehicle.

for vehicle_id, vehicle_data in probdata['vehicles'].items():        
        vehicle = SDDPVehicle( vehicle_id )
        vehicle.initial_location = model.get_location_by_id( vehicle_data['initial_location'] )
        vehicle.aux['speed'] = vehicle_data['speed']

        if vehicle.initial_location is None:
            raise ModelError( f'unknown initial location for order {vehicle_id}: {vehicle_data["initial_location"]}' )

        model.add_vehicle( vehicle )

---

Custom callbacks

The on_vehicle_arrival and the on_order_request callbacks of the model are customized to impose decision points on order requests and on vehicle arrivals.

Vehicle arrivalOrder request

def on_vehicle_arrival( self, vehicle:Vehicle ) -> None:
    """
    "(...) epoch occurs (...) as a result of (...) the following:
        1. a vehicle arrives at the depot (...)"
    """
    # check arrival at the depot from other location
    if vehicle.current_location.id == 'depot' and vehicle.previous_location.id != 'depot':
        self.request_for_routing()

def on_order_request( self, order:Order ) -> None:
    """
    "(...) epoch occurs (...) as a result of (...) the following:
        2. a new request arrives and at least one vehicle is waiting at the depot."
    """
    if any( vehicle for vehicle in self.vehicles if vehicle.is_idle and vehicle.current_visit.location.id == 'depot' and not vehicle.has_next_visit ):
        self.request_for_routing()