or-tools: dirrerent slack_max for some locations - or-tools

Question

In my project I use or-tools for solving VRPTW problem.
I need to set different waiting time for different nodes.
For example. I have 6 locations.
Depot of vehicle. With max time window (0, 1440)
Pickup point for client 1. Time window (0, 10)
Delivery point for client 1. Time window (0, 50)
Pickup point for client 2. Time window (500, 510)
Delivery point for client 2. Time window (500, 600)
Vehicle service point. With max time window (0, 1440)
If I set slack_max with addDimension
routing.addDimension(transitCallbackIndex, // transit callback
1440, // allow waiting time
60 * 24 * 2,
false, // start cumul to zero
"Time");
My vehicle can wait time in range (0, 1440) in each location. In that case time goes of out range time windows of pickup/delivery node . How can I set slack only for Vehicle service point, because time window for that node is max?
I tried set slack like this
if (index == 5) {
timeDimension.slackVar(index).setRange(0, 1440);
}
but that doesn't work as I expected.
Full code sample:
package test;
import com.google.ortools.Loader;
import com.google.ortools.constraintsolver.Assignment;
import com.google.ortools.constraintsolver.FirstSolutionStrategy;
import com.google.ortools.constraintsolver.IntVar;
import com.google.ortools.constraintsolver.IntervalVar;
import com.google.ortools.constraintsolver.RoutingDimension;
import com.google.ortools.constraintsolver.RoutingIndexManager;
import com.google.ortools.constraintsolver.RoutingModel;
import com.google.ortools.constraintsolver.RoutingSearchParameters;
import com.google.ortools.constraintsolver.Solver;
import com.google.ortools.constraintsolver.main;
import java.util.Arrays;
import java.util.logging.Logger;
/** Minimal VRP with Resource Constraints.*/
public class Test {
// static {
// System.loadLibrary("jniortools");
// }
private static final Logger logger = Logger.getLogger(Test.class.getName());
static class DataModel {
public final long[][] timeMatrix = {
{0, 0, 0, 0, 0, 0},
{0, 0, 10, 0, 10, 0},
{0, 10, 0, 10, 0, 0},
{0, 0, 10, 0, 10, 0},
{0, 10, 0, 10, 0, 0},
{0, 0, 0, 0, 0, 0}
};
public final long[][] timeWindows = {
{0, 1440},
{0, 10}, // 1 from
{0, 50}, // 1 to
{500, 510}, // 2 from
{500, 600}, // 2 to
{0, 1440}, // rest location
};
public final int[][] pickupDeliveries = {
{1, 2},
{3, 4},
};
public final int vehicleNumber = 1;
public final int depot = 0;
}
public static void main(String[] args) throws Exception {
Loader.loadNativeLibraries();
// Instantiate the data problem.
final DataModel data = new DataModel();
// Create Routing Index Manager
RoutingIndexManager manager =
new RoutingIndexManager(data.timeMatrix.length, data.vehicleNumber, data.depot);
// Create Routing Model.
RoutingModel routing = new RoutingModel(manager);
Solver solver = routing.solver();
// 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.timeMatrix[fromNode][toNode];
});
// Define cost of each arc.
routing.setArcCostEvaluatorOfAllVehicles(transitCallbackIndex);
// Add Time constraint.
routing.addDimension(transitCallbackIndex, // transit callback
1440, // allow waiting time
60 * 24 * 2,
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.length; ++i) {
long index = manager.nodeToIndex(i);
if (index >= 0) {
timeDimension.cumulVar(index).setRange(data.timeWindows[i][0], data.timeWindows[i][1]);
}
if (index == 5) {
timeDimension.slackVar(index).setRange(0, 1440);
}
}
// 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)));
}
// Define Transportation Requests.
for (int[] request : data.pickupDeliveries) {
long pickupIndex = manager.nodeToIndex(request[0]);
long deliveryIndex = manager.nodeToIndex(request[1]);
routing.addPickupAndDelivery(pickupIndex, deliveryIndex);
solver.addConstraint(
solver.makeEquality(routing.vehicleVar(pickupIndex), routing.vehicleVar(deliveryIndex)));
solver.addConstraint(solver.makeLessOrEqual(
timeDimension.cumulVar(pickupIndex), timeDimension.cumulVar(deliveryIndex)));
}
// Setting first solution heuristic.
RoutingSearchParameters searchParameters =
main.defaultRoutingSearchParameters()
.toBuilder()
.setFirstSolutionStrategy(FirstSolutionStrategy.Value.PATH_CHEAPEST_ARC)
.build();
// Solve the problem.
Assignment solution = routing.solveWithParameters(searchParameters);
if (solution == null) {
System.err.println("No solution found");
return;
}
// Print solution on console.
printSolution(data, routing, manager, solution);
}
/// #brief Print the solution.
static void printSolution(
DataModel data, RoutingModel routing, RoutingIndexManager manager, Assignment solution) {
RoutingDimension timeDimension = routing.getMutableDimension("Time");
long totalTime = 0;
for (int i = 0; i < data.vehicleNumber; ++i) {
long index = routing.start(i);
logger.info("Route for Vehicle " + i + ":");
String route = "";
while (!routing.isEnd(index)) {
IntVar timeVar = timeDimension.cumulVar(index);
route += manager.indexToNode(index) + " Time(" + solution.min(timeVar) + ","
+ solution.max(timeVar) + ") -> ";
index = solution.value(routing.nextVar(index));
}
IntVar timeVar = timeDimension.cumulVar(index);
route += manager.indexToNode(index) + " Time(" + solution.min(timeVar) + ","
+ solution.max(timeVar) + ")";
logger.info(route);
logger.info("Time of the route: " + solution.min(timeVar) + "min");
totalTime += solution.min(timeVar);
}
logger.info("Total time of all routes: " + totalTime + "min");
}
}

Answer 1

In your code:
// Add time window constraints for each location except depot.
for (int i = 1; i < data.timeWindows.length; ++i) {
long index = manager.nodeToIndex(i);
if (index >= 0) {
timeDimension.cumulVar(index).setRange(data.timeWindows[i][0], data.timeWindows[i][1]);
}
if (index == 5) {
timeDimension.slackVar(index).setRange(0, 1440);
}
}
I think:
here your if conditions should use i,
since your loop start at 1 you already skip the depot (node 0),
your timeWindows structure already contains [0, 1440] for node 5.
to force slack to zero for P&D nodes you should use SetValue()
So you could rewrite it like this:
// Add time window constraints for each location except depot.
for (int i = 1; i < data.timeWindows.length; ++i) {
long index = manager.nodeToIndex(i);
timeDimension.cumulVar(index).setRange(data.timeWindows[i][0], data.timeWindows[i][1]);
if (i == 5) {
timeDimension.slackVar(index).setRange(data.timeWindows[i][0], data.timeWindows[i][1]);
} else { // disable waiting time for Pickup&Drop location
timeDimension.slackVar(index).setValue(0);
}
}
possible output:
$ mvn exec:java
[INFO] --- exec-maven-plugin:3.0.0:java (default-cli) # test ---
Dec 22, 2020 12:40:45 PM Test printSolution
INFO: Route for Vehicle 0:
Dec 22, 2020 12:40:45 PM Test printSolution
INFO: 0 Time(0,0) -> 1 Time(0,10) -> 2 Time(10,20) -> 5 Time(10,20) -> 3 Time(500,500) -> 4 Time(510,510) -> 0 Time(510,510)
Dec 22, 2020 12:40:45 PM Test printSolution
INFO: Time of the route: 510min
Dec 22, 2020 12:40:45 PM Test printSolution
INFO: Total time of all routes: 510min
So last question, what do you means by "but that doesn't work as I expected."
What is the observed output and what did you expect ?