谷歌最小成本流解决交通流问题

假设我们有以下数据来解决运输问题:

          A1      A2      A3      Supply
T1        0       600     100     700
T2        500     0       300     800
Demand    500     600     400

我想用谷歌优化工具最小成本流来解决运输问题。我正试图用以下代码来解决这个问题:

    private static void SolveMinCostFlow()
    {
        // Define four parallel arrays: sources, destinations, capacities, and unit costs
        // between each pair. For instance, the arc from node 0 to node 1 has a
        // capacity of 15.
        // Problem taken From Taha's 'Introduction to Operations Research',
        // example 6.4-2.

        int numNodes = 5;
        int numArcs = 6;
        int[] startNodes = { 0, 0, 0, 1, 1, 1 };
        int[] endNodes = { 2, 3, 4, 2, 3, 4};
        int[] capacities = { 500, 600, 400, 500, 600, 400 };
        int[] unitCosts = { 0, 600, 100, 500, 0, 300 };

        // Define an array of supplies at each node.

        int[] supplies = { 700, 700, 800, 800, 800 };



        // Instantiate a SimpleMinCostFlow solver.
        MinCostFlow minCostFlow = new MinCostFlow();

        // Add each arc.
        for (int i = 0; i < numArcs; ++i)
        {
            int arc = minCostFlow.AddArcWithCapacityAndUnitCost(startNodes[i], endNodes[i],
                                                 capacities[i], unitCosts[i]);
            if (arc != i) throw new Exception("Internal error");
        }

        // Add node supplies.
        for (int i = 0; i < numNodes; ++i)
        {
            minCostFlow.SetNodeSupply(i, supplies[i]);
        }


        //Console.WriteLine("Solving min cost flow with " + numNodes + " nodes, and " +
        //                  numArcs + " arcs, source=" + source + ", sink=" + sink);

        // Find the min cost flow.
        int solveStatus = minCostFlow.Solve();
        if (solveStatus == MinCostFlow.OPTIMAL)
        {
            long optimalCost = minCostFlow.OptimalCost();
            Console.WriteLine("Minimum cost: " + optimalCost);
            Console.WriteLine("");
            Console.WriteLine(" Edge   Flow / Capacity  Cost");
            for (int i = 0; i < numArcs; ++i)
            {
                long cost = minCostFlow.Flow(i) * minCostFlow.UnitCost(i);
                Console.WriteLine(minCostFlow.Tail(i) + " -> " +
                                  minCostFlow.Head(i) + "  " +
                                  string.Format("{0,3}", minCostFlow.Flow(i)) + "  / " +
                                  string.Format("{0,3}", minCostFlow.Capacity(i)) + "       " +
                                  string.Format("{0,3}", cost));
            }
        }
        else
        {
            Console.WriteLine("Solving the min cost flow problem failed. Solver status: " +
                              solveStatus);
        }
    }

    static void Main(string[] args)
    {
        SolveMinCostFlow();
        Console.Read();
    }

但我得到了一个错误:解决最小成本流问题失败了。解算器状态:4 我做错了什么?我想在SolveMinCostFlow的开头应该有一些定义参数的东西,但无法理解。