[MITgcm-devel] JFNK

[Martin Losch]

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