[Trilinos-Users] Using Belos in place of AztecOO

[Eric Marttila]

I have been using AztecOO in my code and am interested in using Belos 
instead (with the goal of switching over to using TPetra and MuLue as 
well at some point in the future).

I have been using AztecOO with ML to perform linear solves within a 
non-linear outer iteration loop.  Because my 'A' matrix sometimes 
changes significantly in the outer iteration loop, I end up having to 
recompute the ML preconditioner periodically.

I've attached some psuedocode for my approch using AzteccOO, as well 
as psuedocode for my current approach using Belos.  (see attached 
aztec.cpp and belos.cpp)  Both of these approaches can be summarized 
as:

   1. Create A, x, b
   2. Do initial fill of A and B
   3. Start outer non-linear loop
          3.1. Update values in A and b
          3.2. Create or Recompute preconditioner if needed.
          3.2. Solve linear system
          3.3. Repeat previous steps until convergence

The question I have is related to my use of Belos, where it appears 
that I have to recreate the Belos linear problem each time that my A 
matrix changes in the outer iteration loop.  Is that the right thing 
to do? That was not necessary when using AztecOO, and I am concerned 
that I'm adding a lot of overhead by recreating these objects, and 
especially by calling the 'setProblem()' methods.

I would appreaciate any advice regarding my usage of Belos in 
this manner.

Thank you,
--Eric
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