How to fix Null Point Exception in Google Or-Tools solution?

Question

When i create test for Google Or-Tools and send my distance matrix, solution the solution is always null.

When i use default distance matrix from here https://developers.google.com/optimization/routing/vrp but when i use my custom distanceMatrix array Assigment solution is always null.

Where is mistake?

Full test class

import com.google.ortools.constraintsolver.*;
import org.junit.FixMethodOrder;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.MethodSorters;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.logging.Logger;

@RunWith(SpringRunner.class)
@SpringBootTest
@FixMethodOrder(MethodSorters.NAME_ASCENDING)
public class OrToolsTests {

    private static final Logger logger = Logger.getLogger(OrToolsTests.class.getName());

    static {
        System.loadLibrary("jniortools");
    }

    @Test
    public void b_googleOrTools() throws Exception {
        // Instantiate the data problem.
        final DataModel data = new DataModel();

        // Create Routing Index Manager
        RoutingIndexManager manager =
                new RoutingIndexManager(data.data.length, data.vehicleNumber, data.depot);

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

        // Create and register a transit callback.
        final int transitCallbackIndex =
                routing.registerTransitCallback((long fromIndex, long toIndex) -> {
                    // Convert from routing variable Index to user NodeIndex.
                    int fromNode = manager.indexToNode(fromIndex);
                    int toNode = manager.indexToNode(toIndex);
                    return data.data[fromNode][toNode];
                });

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

        // Add Distance constraint.
        routing.addDimension(transitCallbackIndex, 0, 3000,
                true, // start cumul to zero
                "Distance");
        RoutingDimension distanceDimension = routing.getMutableDimension("Distance");
        distanceDimension.setGlobalSpanCostCoefficient(100);

        // Setting first solution heuristic.
        RoutingSearchParameters searchParameters =
                main.defaultRoutingSearchParameters()
                        .toBuilder()
                        .setFirstSolutionStrategy(FirstSolutionStrategy.Value.PATH_CHEAPEST_ARC)
                        .build();

        // Solve the problem.
        Assignment solution = routing.solveWithParameters(searchParameters);

        // Print solution on console.
        printSolution(data, routing, manager, solution);
    }

    private void printSolution(
            DataModel data, RoutingModel routing, RoutingIndexManager manager, Assignment solution) {
        // Inspect solution.
        long maxRouteDistance = 0;
        for (int i = 0; i < data.vehicleNumber; ++i) {
            long index = routing.start(i);
            logger.info("Route for Vehicle " + i + ":");
            long routeDistance = 0;
            String route = "";
            while (!routing.isEnd(index)) {
                route += manager.indexToNode(index) + " -> ";
                long previousIndex = index;
                index = solution.value(routing.nextVar(index));
                routeDistance += routing.getArcCostForVehicle(previousIndex, index, i);
            }
            logger.info(route + manager.indexToNode(index));
            logger.info("Distance of the route: " + routeDistance + "m");
            maxRouteDistance = Math.max(routeDistance, maxRouteDistance);
        }
        logger.info("Maximum of the route distances: " + maxRouteDistance + "m");
    }

    class DataModel {
        public final long[][] data = {
                {0, 58305, 41338, 16599, 22834, 36364, 24979, 9797, 22023, 5880, 21282, 39248},
                {58147, 0, 82634, 49102, 39605, 93558, 72909, 49687, 67379, 55889, 76274, 22047},
                {41663, 81167, 0, 47046, 58798, 56366, 18071, 41586, 60532, 36117, 49432, 74933},
                {15666, 49990, 53000, 0, 7358, 51077, 30428, 13558, 34534, 13408, 33793, 30933},
                {22151, 39552, 59486, 7391, 0, 57563, 36914, 20043, 41019, 19893, 40278, 24535},
                {36164, 93036, 56237, 51331, 57566, 0, 37419, 44529, 44381, 41822, 17567, 73980},
                {25224, 72585, 18046, 30880, 37115, 37483, 0, 25147, 44093, 19678, 30549, 53529},
                {9218, 49544, 41424, 13485, 19719, 44630, 25065, 0, 28086, 5966, 27345, 30488},
                {22816, 72597, 60379, 34430, 40665, 44423, 44020, 27629, 0, 24921, 27138, 57079},
                {6858, 56163, 36826, 14458, 20693, 42270, 20467, 6781, 25726, 0, 24985, 37107},
                {22678, 75998, 49002, 34292, 40527, 17284, 30184, 27490, 27342, 24783, 0, 56941},
                {38986, 22165, 76018, 29941, 24347, 74398, 53749, 30526, 57854, 36728, 57113, 0}};
        public final int vehicleNumber = 4;
        public final int depot = 0;
    }
}

If you get an exception you should post the stack trace and point out on what row in your code the exception occurs. — Joakim Danielson, May 28 '19 at 07:30
A null solution is the sign that the solver did not find any solution. Therefore, first you should protect your code so that it does not try to display the solution if it is null. Then you need to debug why your model is infeasible (not enough vehicles, route constraints too tight...) — Laurent Perron, May 28 '19 at 21:53

score 1 · Answer 1 · answered May 28 '19 at 21:57

1

From what I understand, you add a dimension with a max cumul of 3000, while the distance matrix has a lot of inter-node distances above 10k.

answered May 28 '19 at 21:57

Laurent Perron

8,594
1
8
22

score 1 · Answer 2 · answered May 29 '19 at 07:25

The 3000 value in #addDimension represents the vehicle maximum travel distance. Since the values in your distance matrix are higher, or-tools is not able to find a solution.

To fix this you have to change the 3000 value so that it is higher than the highest value in your distance matrix. For example

change

// Add Distance constraint.
routing.addDimension(transitCallbackIndex, 0, 3000,
        true, // start cumul to zero
        "Distance");

to

// Add Distance constraint.
routing.addDimension(transitCallbackIndex, 0, 100000,
        true, // start cumul to zero
        "Distance");

and your code will work.

How to fix Null Point Exception in Google Or-Tools solution?

2 Answers2