ValueRangeProvider on PlanningListVariable

[SER1-CG]

Hey TimeFold team, great work with TimeFold Solver. We love it!

Currently, we try to solve a rich VRP problem, based on your very comprehensive quick-start. We want to reduce the search space by narrowing the assignable Visit classes of a Vehicle. We thought of creating a cached problem fact in our PlanningSolution that precisely captures assignability per vehicle:

@ProblemFactCollectionProperty
private Map<Vehicle, List<Visit>> assignableVisitsForVehicle() {
    return vehicles.stream().collect(
            java.util.stream.Collectors.toMap(vehicle-> vehicle, vehicle -> visits.stream()
                     .filter(visit -> visit.isAssignableToVehicle(vehicle))
                     .toList()));
}

Now, we need to create a ValueRangeProvider on the Vehicle class that specifies the range of its visits using the according map entry of this problem fact. However, it must hold that globally on the solution, no assigned visit of a vehicle is assigned to another vehicle. This before was done via a ValueRangeProvider of visits in solution class. It is unclear to us how to implement this ValueRangeProvider for vehicles that supports this desired behavior: a value range per vehicle that is dependent on static information before optimizing, that forbids overlapping assigned values over the set of vehicles.

I could implement this as a constraint, but it wouldn't make too much sense as there are domain constraints that forbid assigning these - think of working hours of the vehicle that don't align with the availability time window of a visit.

[triceo]

Hello @SER1-CG!

You're right that doing this in a constraint would be painful and unnecessary.
Unfortunately, doing entity value ranges which depend on information in the solution is not very straightforward. Something which we need to improve in the future.

At the moment, I think your best bet is to generate your Visit instances with the value ranges already precomputed. Before you start solving, you can call any code you like and enrich your Visits with any data from the solution.

[SER1-CG]

Hi @triceo
Thanks for this blazingly fast answer. I see the limitations about dependencies of entity value ranges on the solution.

Yes, this is a good suggestion. But how do I make sure?
I statically compute a property from outside in applicableVisits and use it as a ValueRangeProvider while removing the ValueRangerProvider from the PlanningSolution :

class Vehicle {
    ...
    @JsonIdentityReference(alwaysAsId = true)
    @PlanningListVariable(valueRangeProviderRefs = { "applicableVisits" })
    private List<Visit> visits;
 
    @ValueRangeProvider(id = "applicableVisits")
    @JsonIgnore
    public List<Visit> getApplicableVisits() {
        return applicableVisits;
    }
    ...
}

But as far as I am concerned, this does not prohibit overlapping assigned visits: it could be the case that one visit is assigned to two distinct vehicles when visit is applicable to both vehicles.

[triceo]

@PlanningListVariable(valueRangeProviderRefs = { "applicableVisits" })
private List<Visit> visits;

@PlanningListVariable gives you this guarantee out of the box. Each Visit can only be in one list variable, and therefore in only one Vehicle.