Specifying Multiple Depots

[Alastair Andrew]

Hi,

Could anyone give me some advice about how to model multiple depots in a VRP problem. I've got a simple 4 location problem and I want to specify that 2 of the locations are depots. I'm using the Java API so rather than std::pairs I need to use the RoutingModel constructor that takes two arrays (the start depots and end depots). 

final int[] starts = { 0, 1 };
final int[] ends = { 0, 1 };
RoutingModel routing = new RoutingModel(size, 1, starts, ends);

When I run this though I get an error:

[15:14:33] src/constraint_solver/routing.cc:923: Check failed: (vehicles) == (starts.size())

I had thought what I was expressing was that there were two depots, nodes 0 and 1. And that if a route started from 0 then it had to end at 0 (and the same for node 1). I thought the search would choose which depot the vehicle would start from. It appears though that the number of depots has to be the same as the number of vehicles. Is it valid to express that there are several potential depots and the vehicle can choose at most one of them? I.e. basically a disjunction over the depot choice.

Cheers,
Alastair

[Ondrej Sykora]

Hi Alastair,

the starts and ends that you specify in the constructor always match the vehicles in the problem, i.e. the pair (0, 0) in your example is the start/end depot for the first vehicle. The number of vehicles you specify must match the number of starts and ends, so in your case,

final int[] starts = { 0, 1 };
final int[] ends = { 0, 1 }; 

RoutingModel routing = new RoutingModel(size, 2, starts, ends);

should do the trick.

Best,

Ondrej

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Ondrej

[Thomas Masuth]

 

 

Hallo,

If you define depots (starts and ends), you have to define vehicles, which start from these depots. The number of vehicles should be equal to the number of starts and the number of ends. A vehicle can start from one depot and can end at another one.

 

 

Thomas Masuth

phone         +49 421 741 48

 

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[Alastair Andrew]

I think my confusion was about whether you could provide alternative depots for a single vehicle. But I guess what you do is provide as many vehicles as there are depots and apply a cost for using a vehicle, so that it'll effectively just chose one of those vehicles. 

Thanks for all your replies.

A