[MITgcm-devel] JFNK

[Martin Losch]

Hi there,

I checked in what I have, am I am working on a better parallel version of fgmres. In the meantime, the preconditioner is giving me a headache, so the entire system is not really in the best state ... 

M.

On Oct 15, 2012, at 5:18 PM, Jean-Michel Campin wrote:

> Hi Martin,
> 
> This is good news. Please check-in the version you have.
> we can figure out later the multi-treaded issues (if there are some).
> Don't know much about alternative parallel algorithm, but may be others do.
> 
> Cheers,
> Jean-Michel
> 
> On Fri, Oct 12, 2012 at 04:43:37PM +0200, Martin Losch wrote:
>> Hi Jean-Michel, and others
>> 
>> I have implemented a JFNK solver for the sea ice dynamics (following Lemieux et al, 2010, 2012). I have not made too many tests yet, but I think that the serial version works.
>> 
>> Now I need to work on the parallel version and for that I need some help:
>> 1. I have an MPI version runing (almost) that will give you similar results for 1 or 2 cpu, but I have not yet done the multithreading (I hope to have moved all the computation to myThid=1).
>> 2. The JFNK requires a (F)GMRES implementation (with reverse communication). In the routine that I have, the orthogonalization of the Krylov subspaces is done with a modified Gram Schmidt method that requires many scale products and thus global sums. This will break any advantage that a JFNK might bring. The solution appears to use a different orthogonalization (I have seen Householder reflection), but I have absolutely no idea about these things. So far my search for availble parallel FGMRES routines has not been successful.
>> 
>> In order to continue (especially with 1.), I would like to check the present version in, but since it is not fully functional, will probably put a stop somewhere. Are you OK with that? Or should I wait, until I find good parallel FGMRES (maybe with your help?).
>> 
>> Martin
>> 
>> 
>> 
>> 
>> 
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