how to increment num_locations in routing.SolveWithParameters

[bragosso]

I wrote a script to optimize the waste collect management, using python and OR-Tools (last version for both). The script runs in a good ways if the number of location is 200 or less, when i give it the real file with 344 locations, the script end without error or log, it stops.
It stops at this command solution = routing.SolveWithParameters(search_parameters)
I tried to incapsulate in an try except but nothing change
I tried also to change some parameter (like time_limit.seconds) but there was no change.
Did one of you encountered this problem and soleved it ?
Thanlks
Bragosso

[lperron]

You cannot. You need to recreate a model.

[bragosso]

How to recreate ? any suggestion ?
this is the code

# OR-TOOLS per risolvere il TSP - Attenzione gestisce al massimo 200 punti
import psutil
from ortools.constraint_solver import routing_enums_pb2
from ortools.constraint_solver import pywrapcp
from shapely.wkt import loads as wkt_loads
from colorama import Fore, Back, Style
def create_data_model(locations):
    data = {}
    data['locations'] = locations
    data['num_locations'] = len(locations)
    data['depot'] = 0  # Indice del deposito (posizione di partenza)
    return data

def compute_distance(location1, location2):
    # Calcola la distanza euclidea tra due punti di sosta
    point1 = wkt_loads(location1['position'])
    point2 = wkt_loads(location2['position'])
    distance = point1.distance(point2)
    return distance

def create_distance_callback(data):
    # Crea una funzione di callback per calcolare la distanza tra due punti di sosta
    def distance_callback(from_index, to_index):
        from_location = data['locations'][from_index]
        to_location = data['locations'][to_index]
        distance = compute_distance(from_location, to_location)
        return distance
    return distance_callback

def solve_tsp(locations):
    print(Fore.RED + "Crea il routing model " + Style.RESET_ALL + ' ')
    # Risolve il TSP utilizzando OR-Tools
    data = create_data_model(locations)
    print(Fore.RED + "Entro in VRPOR " + Style.RESET_ALL + ' ')
    # Crea il routing model
    manager = pywrapcp.RoutingIndexManager(data['num_locations'], 1, data['depot'])
    # print(data['num_locations'])
    # print(data['depot'])
    routing = pywrapcp.RoutingModel(manager)
    print(Fore.RED + "Crea una matrice delle distanze " + Style.RESET_ALL + ' ')
    # Crea una matrice delle distanze
    distance_callback = create_distance_callback(data)
    transit_callback_index = routing.RegisterTransitCallback(distance_callback)
    routing.SetArcCostEvaluatorOfAllVehicles(transit_callback_index)
    print(Fore.RED + "Imposta i parametri di ricerca " + Style.RESET_ALL + ' ')
    # Imposta i parametri di ricerca
    search_parameters = pywrapcp.DefaultRoutingSearchParameters()
    # print(search_parameters)
    search_parameters.first_solution_strategy = routing_enums_pb2.FirstSolutionStrategy.PATH_CHEAPEST_ARC
    # print(search_parameters)
    print(Fore.RED + "Risolve il problema " + Style.RESET_ALL + ' ')
    # Risolve il problema
    try:
        solution = routing.SolveWithParameters(search_parameters)
    except:
        print(Fore.RED + "Errore in SolveWithParameters " + Style.RESET_ALL + ' ')
    print(Fore.RED + "Costruisce la lista ordinata dei punti di sosta " + Style.RESET_ALL + ' ')
    # Costruisce la lista ordinata dei punti di sosta
    ordered_locations = []
    index = routing.Start(0)
    while not routing.IsEnd(index):
        ordered_locations.append(data['locations'][index])
        index = solution.Value(routing.NextVar(index))
    ordered_locations.append(data['locations'][manager.IndexToNode(index)])

    print(Fore.RED + "Esco da VRPOR " + Style.RESET_ALL + ' ')
    return ordered_locations

[jmarca]

I'm not 100% sure of what you are asking. Are you saying the above script works fine with 200 nodes, but fails with 300+?

Try turning on logging to see what is going on.

        search_parameters = pywrapcp.DefaultRoutingSearchParameters()
        search_parameters.log_search = True

Also, your distance matrix is incredibly inefficient. Every time the solver needs a distance, it has to run some code. One simple fix is to run all to all once and store that in a lookup matrix. But that is still terrible, because crossing from C++ to python is slow, and you are asking it to do that a lot with a large problem. Even better is to turn on caching so that the distance lookups for the dimensions are just called the minimum number of times needed from the C++.

       model_parameters = pywrapcp.DefaultRoutingModelParameters()
       model_parameters.max_callback_cache_size = 2 * num_nodes  
       ...
        routing = pywrapcp.RoutingModel(manager, model_parameters)

[bragosso]

Thanks, I'll try
I'm new to python and to OR-Tools, so the problem you mentioned are real ...