what's the difference between {split volume} {subtract(boolean)} in gambit
 

I am the newer of gambit, and I do the exercise according to http://cfd.mae.wvu.edu/mae433/PDFs/F...20exercise.pdf

In the first place, it makes the outer_cylinder splitted by the inner_cylinder. But in my experience, I always do that using Boolean cooperation. what's the difference? Thanks.

there is no difference, BUT boolean operations only work on real volumes.
If your geometry becomes virtual after some merge or clean operations, then you cannot use Boolean operations. But you can still use split operations (more difficult with virtual than real, but it works).
I only use boolean operations (substrat) for extracting fluid domain from CAD.

I take pleasure in knowing that :)
and Many thanks for your quick response.