[petsc-users] Convergence is different with different processors

[Hui Zhang]

From my understanding of the bjacobi, it is a block Jacobi method with each block corresponding to a processor.
What I can not understand is why you get convergence with eight blocks but divergence with four (fewer) blocks.
Which directory is the program ex4f from?


On Feb 16, 2013, at 6:36 PM, w_ang_temp wrote:

> 
> 
> I use the two commands in the same project. The first is divergent while the second is convergent.
> nohup mpiexec -n 4 ./ex4f -ksp_type bcgs -pc_type bjacobi -ksp_rtol 1.0e-5 -ksp_converged_reason >out.txt &
> nohup mpiexec -n 8 ./ex4f -ksp_type bcgs -pc_type bjacobi -ksp_rtol 1.0e-5 -ksp_converged_reason >out.txt &
> So what is the reason?
> Thanks.                    Jim
> 
> 
> 
> >> 2013-02-07 13:16:51，"Matthew Knepley" <knepley at gmail.com> 写道：
> >> On Thu, Feb 7, 2013 at 12:11 AM, w_ang_temp <w_ang_temp at 163.com> wrote:
> >> Hello,
> >>     I use the same project, but I find that when different number of processors is choosed,
> >> the convergence is different. For example, when the processors are 4, it is divergent; when
> >> the processors are 8, it is convergent.
> >>     So what is the reason?
> 
> >It is likely that your preconditioner changed.
> 
>   > Matt
>  
> >>     Thanks.
> >>                                    Jim.
> 
> 
> 
> 
> 
> -- 
> 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
> 
>