On Mon, Jun 22, 2015 at 5:04 AM, Orxan Shibliyev <orxan.shibli@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