Steps for loading CVRPLIB into Ecole as an Instance

[ndrwnaguib]

Hi,

I am trying to load CVRPLIB into Ecole. However, I do not think designing it as an instance generator is the way. I view it as a loader instead. I'm not sure what steps I should follow to achieve that, I'd appreciate any pointers.

Off topic: if you believe there would be considerable use for these datasets, I also would like to contribute it to Ecole problem instances.

Thank you.

[AntoinePrv]

Hi @ndrwnaguib

It seems these files are of type .vrp, but I am not sure what their structure is / how to read them. Do you know how they are typically read? Do you have a reference to a parser/loader that can read these files?
I imagine that if they're not written as MILPs, it's that their formulation would be too big. Hence it's difficult to parse them into a Model without knowing what solution method would be used (decomposition methods most likely).

[AntoinePrv]

The file you are pointing to is an example file, not part of the library, so we would need to duplicate it.
The file also use a custom pricer. While we are interested in supporting this, it is not something that can be done quickly. Any help is appreciated.

[ndrwnaguib]

Great! I'd love to help. Can you please how can I? Do I prepare a PR? is there a contributing guide? :))

[AntoinePrv]

Sorry for the delay. Unfortunately, Ecole is going in a slow mode, and there is nobody that can look more in details into this.
At a first look, it seem to be that we cannot "just load" these instances like regular ones, otherwise SCIP would have added a loader for them.

[ndrwnaguib]

Sorry for the delay. Unfortunately, Ecole is going in a slow mode, and there is nobody that can look more in details into this.

I see; I will try to work on that on my own until Ecole's development is active again. Thanks for letting me know.

At a first look, it seem to be that we cannot "just load" these instances like regular ones, otherwise SCIP would have added a loader for them.

I'm not sure how is this different than the regular ones; I believe SCIP has a loader for CVRPLIB datasets in https://www.scipopt.org/doc/html/main__vrp_8cpp_source.php. Well, it's an example, but it should work, right?

[AntoinePrv]

My uncertainty is about the pricer on line 425. This makes me wonder that the problem loaded without the pricer might not be a complete one (not an expert here).
So I don't know if we should load them with the pricer or leave that out.