[petsc-users] Very low CFL number for PETSC's GS

[Matthew Knepley]

On Mon, Jun 22, 2015 at 5:04 AM, Orxan Shibliyev <orxan.shibli at gmail.com>
wrote:

> I wanted to compare my own GS and the one of PETSC's. I used KSPRICHARDSON
> with PCSOR to obtain GS. I tested my GS with CFL=40 and solved Ax=b problem
> successfully and fast. However, PETSC failed to solve at CFL=40 and it
> gives an answer only for very low CFL numbers such as 0.1. Of course, the
> convergence was very slow. My question is that if A and b and the
> implementations are the same why PETSC fails to solve with same CFL number
> as for my GS solver?
>
> PS1: My GS solver is a plain GS, no fancy stuff.
> PS2: A is a block matrix (MATSEQBAIJ) for PETSC. Also, the process is
> sequential.
>

1) For any solver question, send the output of

  -ksp_view -ksp_monitor_true_residual -ksp_converged_reason

2) Did you use
http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCSOR.html
and set the options
    so that the algorithm matches yours?

   Matt

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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