Optimization speed is unexpected slow

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Heyy Simone,

Thanks very much for your repo, I like it a lot!

However, when I run Solomon instance C101 with 20 customers on your repo, the solution time would be around 40 minutes, which is a bit too slow, no?
When I ran the same instance with the default Gurobi solver (I am not sure which method it is used, maybe cut-pricing?), it would only take around 1.2 seconds...

Do you have any idea about the reasons for the slow solution time?

BTW My hardware is AMD EPYC 7313P

BW,
Jingsong