[Trilinos-Users] AztecOO convergence

[Hoang Giang Bui]

Hi

Thank you for your reply. I tried AztecOO without preconditioner but the 
convergence is the same. For more information, the problem size I tested 
is 60000 and the convergence test is AZ_r0. The rhs norm is 1.493e+07. 
The krylov space is 1000. The preconditioner doesn't involve any local 
iterative solve.

Any idea could help me to improve this ?

BR
Bui



On 06/24/13 21:28, Heroux, Michael A wrote:
> A few questions:
>
>   * What is your problem size?
>   * What residual test are you using?  In particular, if you are
>     scaling by the RHS and it has a small norm you might be asking for
>     a convergence tolerance that is unachievable in double precision
>     arithmetic.
>
> Mike
>
> From: Hoang Giang Bui <hgbk2008 at gmail.com <mailto:hgbk2008 at gmail.com>>
> Date: Monday, June 24, 2013 1:02 PM
> To: "trilinos-users at software.sandia.gov 
> <mailto:trilinos-users at software.sandia.gov>" 
> <trilinos-users at software.sandia.gov 
> <mailto:trilinos-users at software.sandia.gov>>
> Subject: [Trilinos-Users] AztecOO convergence
>
>
> Hi
>
> When using AztecOO with user defined preconditioner. I obtained 
> convergence behaviour like this:
>
>
> *******************************************************
> ***** Problem: Epetra::CrsMatrix
> ***** Preconditioned GMRES solution
> ***** N4Teko22BlockLowerTriInverseOpE
> ***** No scaling
> *******************************************************
>          iter: 0 residual = 1.000000e+00
>          iter: 100 residual = 1.698526e-03
>          iter: 200 residual = 3.441675e-04
>          iter: 300 residual = 4.356401e-05
>          iter: 400 residual = 3.333877e-05
>          iter: 500 residual = 1.901319e-05
>          iter: 600 residual = 1.574073e-05
>          iter: 700 residual = 1.438600e-05
>          iter: 800 residual = 1.372764e-05
>          iter: 900 residual = 1.351302e-05
>          iter: 1000 residual = 1.335775e-05 
> ***************************************************************
> Warning: maximum number of iterations exceeded without convergence
> Solver: gmres
> number of iterations: 1000
> Recursive residual = 3.6551e-08
>
> The convergence rate at iteration > 200 is very slow. In this case, 
> what should I do to improve the convergence rate of Gmres?
>
> BR
> Bui
>

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