[petsc-users] AO versus DM for 3D CG solve

[Jed Brown]

On Sep 6, 2012 1:12 PM, "Ronald M. Caplan" <caplanr at predsci.com> wrote:
>
> Hi,
>
> I am trying to implement petsc into an existing (very large) FORTRAN code
which splits a 3D grid in each dimension (so for a 100x100x100 problem on 4
cores, each core gets a 25x25x25 part of the grid).

Do you mean 4^3 = 64 cores?

>
> The default partitioning for petsc just assigns contiguous rows of the
coefficient matrix to each core which is hampering performance.
>
> From looking around I have found that there are AO routines and DM
routines in petsc.
>
> What is the difference between using either of them for my problem?
> Should I be using DM to partition the petsc matrices/vectors so that they
match the grid points on each node, or do I use AO routines to do that?
> Or do AO routines just map the default petsc partitioning indices to my
problem's indices in which case I want to use DM?
>
> Thanks
>
> Ron Caplan
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