Amesos2: Repeated map construction

[cgcgcg]

Enhancement

MueLu uses` Amesos2 for coarse solves. This means that the same linear system is solved repeatedly. Only the RHS changes.

Trilinos/packages/amesos2/src/Amesos2_MultiVecAdapter_def.hpp

Lines 353 to 358 in fc8b056

	const Teuchos::RCP<const Tpetra::Map<lo_t,go_t,node_t> > map
	= Amesos2::Util::getDistributionMap<lo_t,go_t,gs_t,node_t>(distribution,
	mv->getGlobalLength(),
	mv->getComm(),
	indexBase,
	mv->getMap());

constructs a map for each solve. Is that necessary or could this step be cached? Or is MueLu using Amesos2 incorrectly?

[iyamazaki]

Thank you, @cgcgcg. I think there are some short-cuts for special cases (like if your coarse-space vector is already on a single MPI and contiguous). But, it will be nice if we can cache the map, especially for solve. I'll see where to store, and when to recompute the map (e.g., when it does not match with mv->getMap()?). I think these routines are trying to cover lots of corner cases @ndellingwood.