Google Or-Tools Routing - Solution为空

Question

我正在尝试实现谷歌或工具的VRPTW。但我正面临着一个问题。当我传递动态时间矩阵时，解决方案对象为空，但是当我传递示例中给出的时间矩阵时，它就起作用了。

以下是我的代码

 public class DataModel
    {
        public long[,] DistanceMatrix { get; set; }
        public long[,] TimeMatrix = {
            //commented matrix is dynamic generated
  // {0,5,20,10,0,5},  
  //{5,0,25,10,5,5},
  //{20,25,0,30,20,20},
  //{10,10,30,0,10,15},
  //{0,5,20,10,0,5},
  //{5,5,20,15,5,0},
    {0, 6, 9, 8, 7, 3},
  {6, 0, 8, 3, 2, 6},
  {9, 8, 0, 11, 10, 6},
  {8, 3, 11, 0, 1, 7},
  {7, 2, 10, 1, 0, 6},
  {3, 6, 6, 7, 6, 0},
};
        public long[,] TimeWindows = {
  {0, 5},    // depot
  {7, 12},   // 1
  {10, 15},  // 2
  {16, 18},  // 3
  {10, 13},  // 4
  {0, 5},    // 5
};
        public int VehicleNumber = 3;
        public int Depot = 0;
    };

下面是主要的函数代码

DataModel data = new DataModel();
            // data.TimeMatrix = TimeMatrix;
            // Create Routing Index Manager
            RoutingIndexManager manager = new RoutingIndexManager(
                data.TimeMatrix.GetLength(0),
                data.VehicleNumber,
                data.Depot);

            // Create a Routing Model.
            RoutingModel routing = new RoutingModel(manager);

            // Create and register a transit callback.
            int transitCallbackIndex = routing.RegisterTransitCallback(
                (long fromIndex, long toIndex) =>
                {
                    // Convert from routing variable Index to distance matrix NodeIndex.
                    var fromNode = manager.IndexToNode(fromIndex);
                    var toNode = manager.IndexToNode(toIndex);
                    return data.TimeMatrix[fromNode, toNode];
                }
                );

            // Define the cost of each arc.
            routing.SetArcCostEvaluatorOfAllVehicles(transitCallbackIndex);

            // Add Distance constraint.
            routing.AddDimension(
                transitCallbackIndex, // transit callback
                30, // allow waiting time
                30, // vehicle maximum capacities
                false,  // start cumul to zero
                "Time");
            RoutingDimension timeDimension = routing.GetMutableDimension("Time");
            // Add time window constraints for each location except depot.
            for (int i = 1; i < data.TimeWindows.GetLength(0); ++i)
            {
                long index = manager.NodeToIndex(i);
                timeDimension.CumulVar(index).SetRange(
                    data.TimeWindows[i, 0],
                    data.TimeWindows[i, 1]);
            }
            // Add time window constraints for each vehicle start node.
            for (int i = 0; i < data.VehicleNumber; ++i)
            {
                long index = routing.Start(i);
                timeDimension.CumulVar(index).SetRange(
                    data.TimeWindows[0, 0],
                    data.TimeWindows[0, 1]);
            }

            // Instantiate route start and end times to produce feasible times.
            for (int i = 0; i < data.VehicleNumber; ++i)
            {
                routing.AddVariableMinimizedByFinalizer(
                    timeDimension.CumulVar(routing.Start(i)));
                routing.AddVariableMinimizedByFinalizer(
                    timeDimension.CumulVar(routing.End(i)));
            }

            // Setting first solution heuristic.
            RoutingSearchParameters searchParameters =
              operations_research_constraint_solver.DefaultRoutingSearchParameters();
            searchParameters.FirstSolutionStrategy =
              FirstSolutionStrategy.Types.Value.PathCheapestArc;

            // Solve the problem.
            Assignment solution = routing.SolveWithParameters(searchParameters);  //it is null when dynamic time matrix is used, but it is not null when time matrix mentioned in example is used.

问题似乎出在AddDimension方法中。我对此感到震惊，但找不到任何解决方案。请提出任何解决方案。

Answer 1

solution is null表示求解器找不到任何可行的解。很可能你的时间窗口太紧了。

要么试着放松你的时间窗

或者确保节点是可选的(使用addDisjunction)。