Multi Depot Routing

[Divya Manikantan]

I have few depots, amnd all vehicles will start and end based on their nearest depot , but the issue I am facing is I have too keep num vehicles same as num depots or python crashes without any error. Example 2 depots then 2 vehicles, how do I solve this problem?

[Mizux Seiha]

When using the override method: 
 RoutingIndexManager(int num_nodes, int num_vehicles,
                      const std::vector<NodeIndex>& starts,
                      const std::vector<NodeIndex>& ends);

What is your problem to fulfill the constraint:
starts.size() == ends.size() == num_vehicles ?

If you have 2 vehicles starting from A, two vehicles starting from B, and all vehicles finishing at C then you can write:
RoutingIndexManager(
...., # num locations
/*num_vehicles=*/4, 
/*starts=*/[A, A, B, B],
/*ends=*/[C, C, C, C])

[Divya Manikantan]

Thanks for the input, my query is that, I want to dynamically choose the start and end depots, based on minimum distance example I have 2 depots A,B and suppose order is to be picked from X and delivered to Y, the start and end depots to be determined based on proximity to the pickup or drop. Example X is closer to B and Y is closer to A then, B --> X ---> Y ---> A, is this possible?

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[Huib Donkers]

I see my previous message was deleted, maybe because it look too much like spam, containing only half a sentence and a single link?
Anyway, if I understand correctly, you basically want the solver to have free choice of where vehicles start and end, so it'll pick the depot locations that yield the best objective value (which probably means it'll be the closest depot). You can use/modify the approach described in the "guide" pages on google or-tools. I'd give the link but I tried that before.. You can google for "google or tools common routing tasks" or "google or tools arbitrary start and end locations" to find the page. It doesn't give much information, but the key idea is to set the distance to 0, between your actual depots (nodes) and the node that OR-tools thinks is your (start/end) depot. Technically your routes will still always start and end at the same location, but you modify the graph such that the second and the second-to-last vertices must be one of your depots.

[Divya Manikantan]

Thank you will try this one and update