[Petsc-trilinos-discussion] Scope and requirements

[Bartlett, Roscoe A.]

> > 3) Before Hydra-TH get coupled into any other code, we need to remove
> > the direct insertion of ML support in the PETSc lib and defer it to
> > Hydra-TH or some other downstream lib that uses dependency injection
> > to overcome the link order issue.
> 
> What is the "link order issue"?  AFAIK, ML never depends on PETSc, so
> there is no dependency loop.  In any case, registering the ML plugin
> later is a pure build system issue (no source code changes).

[Bartlett, Roscoe A.] 

ML gets built along with the rest of Trilinos as a TriBITS package in VERA where PETSc is treated as a pre-built static TPL.  This is done because changes are being made to Trilinos to drive CASL work but not for PETSc.   Building PETSc downstream from Trilinos would mean wrapping PETSc as a TriBITS package and we don't want to go there unless we are forced to do so.  There are a lot of complexities and regrets when you have to do this (as our experience with MOOSE is showing).

-Ross