VRP with time window constraints - What unit of time?

[Hanna Hamilton]

Hi there - I am looking at the implementation here: https://developers.google.com/optimization/routing/vrptw

In the following lines of code, is there a certain unit of time that this implementation assumes (e.g. 30 minutes?)? I am wondering about this since I have my data in half hours, so I will need to make sure that everything is in half hours.

Also, what does "Don't force start cumul to zero." mean?

# Add Time Windows constraint.
    time = 'Time'
    routing.AddDimension(
        transit_callback_index,
        30,  # allow waiting time
        30,  # maximum time per vehicle
        False,  # Don't force start cumul to zero.
        time)
    time_dimension = routing.GetDimensionOrDie(time)

Thanks,

Hanna

[Laurent Perron]

There is no definition of unit of time in the routing library.

You decide what 1 unit of time means.

Laurent Perron | Operations Research | lpe...@google.com | (33) 1 42 68 53 00

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[Mizux Seiha]

In AddDimension() if you set "force start cumul to zero" to TRUE it means the TW for each vehicle start node will be set to [0, 0] aka cumulVar for any start node is "forced" to zero...

This is useful for distance dimension or duration dimension BUT for time dimension you usually don't want this behavior, e.g. supposing you want your vehicle to start at 8h00am and not forcing it at 0h00am

[Hanna Hamilton]

Okay, got it. Thanks!