[Trilinos-Users] Trouble Ensuring x (as Guess) is used in Belos Solver

[Corey A. Henderson]

I did not. I was going to ping the thread to be sure it had been seen.

I am still not able to convince myself that x is being used as a guess.

On Sat, Feb 9, 2019, 8:19 PM Heroux, Mike <MHeroux at csbsju.edu wrote:

> Corey,
>
>
>
> Did you get past this issue?  Messages being sent to
> trilinos-users at trilinos.org are not being reliably received by everyone
> on the list.
>
>
>
> Thanks.
>
>
>
> Mike
>
>
>
>
>
> *From: *Trilinos-Users <trilinos-users-bounces at trilinos.org> on behalf of
> "Corey A. Henderson" <cahenderson at wisc.edu>
> *Date: *Wednesday, December 26, 2018 at 1:30 PM
> *To: *"trilinos-users at trilinos.org" <trilinos-users at trilinos.org>
> *Subject: *[Trilinos-Users] Trouble Ensuring x (as Guess) is used in
> Belos Solver
>
>
>
> Hello,
>
>
>
> I am trying to set up an iterative call to the Pseudoblock GMRES solver in
> Belos where I expect x to vary only slightly between calls (because b
> varies only slightly). When I inspect the number of iterations after
> subsequent calls, even if b is not changed, I get no reduction in
> iterations as I would expect from using the previous x as a guess. I
> believe I am missing something in how Belos is reset().
>
>
>
> I need some help in learning how to ensure the previously-solved x is
> reused as a guess for subsequent iterations.
>
>
>
> Pseudocode:
>
>
>
> Set up A, x=0, preconditioner M, initial b
>
> Create problem from M, A, x, b
>
> Create solver ("GMRES")
>
> Solver.setProblem()
>
> loop
>
>     solve()
>
>     print numIters
>
>     copy off of x
>
>     Solver.reset(Problem)  <-- Where I think my mistake is
>
>     update b
>
> end loop
>
>
>
> Even if b is unchanged, I get the same number of iterations (and duration)
> on subsequent solves, where I would expect them to drop significantly since
> x is near (or just is) the solution. If I omit the solver.reset() call I
> get an error on the next solve(). I believe x is not being used as a guess
> the way I'm setting up my code, but I don't understand why.
>
>
>
> Can someone explain how to ensure Belos uses x as a guess? I have been
> over the documentation and can't figure it what I'm doing wrong.
>
>
>
> Thanks!
>
>
>
> Corey
>
> --
>
> Corey A. Henderson
>
> PhD Candidate and NSF Graduate Fellow
>
> Dept. of Engineering Physics
>
> Univ. of Wisconsin - Madison
>
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