clearify semantics of preconditioner pre/apply/post
I always assumed that for every
Preconditioner object, it is necessary to call
apply. Then it is safe to call
apply as often as necessary to converge and the
post ensures cleanup of temporary data.
The pthread tests in
dune/istl/paamg/test now also test variants, where the
pre is called before cloning the
AMG and the running it in several threads. I'm surprised by this behaviour, and it tests a stronger requirement than I always assumed.
What is the proper behaviour here?