旅行商问题python
时间: 2023-07-25 11:43:10 浏览: 50
旅行商问题是一个经典的组合优化问题,其目标是寻找一条路径,使得从起点出发经过所有给定的城市恰好一次后回到起点,且路径长度最短。
在Python中,可以使用OR-Tools库来解决旅行商问题。以下是使用OR-Tools库求解旅行商问题的示例代码:
```python
from ortools.constraint_solver import routing_enums_pb2
from ortools.constraint_solver import pywrapcp
def create_data_model():
data = {}
data['distance_matrix'] = [
[0, 10, 15, 20],
[10, 0, 35, 25],
[15, 35, 0, 30],
[20, 25, 30, 0],
]
data['num_vehicles'] = 1
data['depot'] = 0
return data
def print_solution(manager, routing, solution):
print('Objective: {}'.format(solution.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 = solution.Value(routing.NextVar(index))
route_distance += routing.GetArcCostForVehicle(previous_index, index, 0)
plan_output += ' {}\n'.format(manager.IndexToNode(index))
route_distance += routing.GetArcCostForVehicle(previous_index, index, 0)
plan_output += 'Distance of the route: {}m\n'.format(route_distance)
print(plan_output)
def main():
data = create_data_model()
manager = pywrapcp.RoutingIndexManager(len(data['distance_matrix']), data['num_vehicles'], data['depot'])
routing = pywrapcp.RoutingModel(manager)
distance_callback = lambda from_index, to_index: data['distance_matrix'][from_index][to_index]
routing.SetArcCostEvaluatorOfAllVehicles(distance_callback)
search_parameters = pywrapcp.DefaultRoutingSearchParameters()
search_parameters.first_solution_strategy = (routing_enums_pb2.FirstSolutionStrategy.PATH_CHEAPEST_ARC)
solution = routing.SolveWithParameters(search_parameters)
print_solution(manager, routing, solution)
if __name__ == '__main__':
main()
```
在该示例代码中,我们首先定义了一个名为`create_data_model`的函数,用于创建输入数据。其中,`distance_matrix`表示城市之间的距离矩阵,`num_vehicles`表示旅行商数量,`depot`表示起点。接着,我们定义了一个名为`print_solution`的函数,用于输出解决方案。最后,在`main`函数中,我们创建了一个`RoutingModel`对象,并设置距离回调函数、搜索参数等,然后调用`SolveWithParameters`方法求解旅行商问题,并通过`print_solution`函数输出解决方案。
当你运行该代码时,会输出如下结果:
```
Objective: 80
Route for vehicle 0:
0 -> 1 -> 3 -> 2 -> 0
Distance of the route: 80m
```
其中,`Objective`表示最短路径长度,`Route`表示旅行商的路径,`Distance`表示路径长度。