[petsc-users] FW: Parallel vs. single processor

[Jed Brown]

1. Please reply to the list rather than me personally.

2. Upgrade to petsc-3.3 for GAMG. You can also use ML or BoomerAMG with
older versions of PETSc.

3. Send full convergence output.

4. Lots of general tips here:
http://scicomp.stackexchange.com/questions/513/why-is-my-iterative-linear-solver-not-converging


On Mon, Nov 12, 2012 at 11:10 AM, Rob Kunz <rfk102 at arl.psu.edu> wrote:

>  Hi Jed:****
>
> Thanks for your response.****
>
> I am currently doing all PETSC call from C.****
>
> Attached is the code snippet I am using based on ex54.c.html.****
>
> I get an error that PCGAMG is undefined.****
>
> Must I do something on the command line?****
>
> Thanks****
>
> Rob****
>
> ** **
>
> ** **
>
> Robert F. Kunz****
>
> Head, Computational Mechanics Division, Applied Research Laboratory****
>
> Professor, Aerospace Engineering****
>
> The Pennsylvania State University****
>
> PO Box 30****
>
> University Park, PA 16804****
>
> rfk102 at arl.psu.edu****
>
> 814-360-1901****
>
> ** **
>
> ** **
>
> ** **
>
> ** **
>
> ** **
>
> ** **
>
> *From:* petsc-users-bounces at mcs.anl.gov [mailto:
> petsc-users-bounces at mcs.anl.gov] *On Behalf Of *Jed Brown
> *Sent:* Monday, November 12, 2012 11:31 AM
> *To:* PETSc users list
> *Subject:* Re: [petsc-users] Parallel vs. single processor****
>
> ** **
>
> Try (e.g., -pc_type gamg) and additive Schwarz. Also try using ASM as a
> smoother.****
>
> ** **
>
> On Mon, Nov 12, 2012 at 10:21 AM, Rob Kunz <rfk102 at arl.psu.edu> wrote:****
>
> Hi:****
>
> I have a pressure based CFD code using PETSC for nearly SPD pressure
> equation.****
>
> PETSC default solver + preconditioner (GMRES+BJ for n-proc) is very
> reliable for me.****
>
> However I have a very tough bearing problem with extremely high aspect
> ratio cells and the 1-processor run works fine (GMRES+ILU0), but for
> nproc>1 the code does not converge.****
>
> Of course I can get the code to return identical 1-proc and 12-proc
> convergence histories if I choose a point preconditioner like Jacobi, but
> that kills the convergence of both.****
>
> Any recommendations?****
>
> Thanks
> Rob Kunz****
>
> ** **
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20121112/1001c4c4/attachment.html>