[petsc-users] Using DMDAs with an assigned domain decomposition to Solve Poisson Equation

[Matthew Knepley]

On Mon, Feb 24, 2020 at 6:35 AM Pierpaolo Minelli <pierpaolo.minelli at cnr.it>
wrote:

>
>
> Il giorno 24 feb 2020, alle ore 12:24, Matthew Knepley <knepley at gmail.com>
> ha scritto:
>
> On Mon, Feb 24, 2020 at 5:30 AM Pierpaolo Minelli <
> pierpaolo.minelli at cnr.it> wrote:
>
>> Hi,
>> I'm developing a 3D code in Fortran to study the space-time evolution of
>> charged particles within a Cartesian domain.
>> The domain decomposition has been made by me taking into account symmetry
>> and load balancing reasons related to my specific problem.
>
>
> That may be a problem. DMDA can only decompose itself along straight lines
> through the domain. Is that how your decomposition looks?
>
>
> My decomposition at the moment is paractically a 2D decomposition because
> i have:
>
> M = 251 (X)
> N = 341 (Y)
> P = 161 (Z)
>
> and if i use 24 MPI procs, i divided my domain in a 3D Cartesian Topology
> with:
>
> m = 4
> n = 6
> p = 1
>
>
>
>
>> In this first draft, it will remain constant throughout my simulation.
>>
>> Is there a way, using DMDAs, to solve Poisson's equation, using the
>> domain decomposition above, obtaining as a result the local solution
>> including its ghost cells values?
>>
>
> How do you discretize the Poisson equation?
>
>
> I intend to use a 7 point stencil like that in this example:
>
>
> https://www.mcs.anl.gov/petsc/petsc-current/src/ksp/ksp/examples/tutorials/ex22f.F90.html
>

Okay, then you can do exactly as Mark says and use that example. This will
allow you to use geometric multigrid
for the Poisson problem. I don't think it can be beaten speed-wise.

  Thanks,

     Matt


>
>   Thanks,
>
>     Matt
>
>
>> As input data at each time-step I know the electric charge density in
>> each local subdomain (RHS), including the ghost cells, even if I don't
>> think they are useful for the calculation of the equation.
>> Matrix coefficients (LHS) and boundary conditions are constant during my
>> simulation.
>>
>> As an output I would need to know the local electrical potential in each
>> local subdomain, including the values of the ghost cells in each
>> dimension(X,Y,Z).
>>
>> Is there an example that I can use in Fortran to solve this kind of
>> problem?
>>
>> Thanks in advance
>>
>> Pierpaolo Minelli
>>
>>
>
>
> Thanks
> Pierpaolo
>
>
> --
> 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
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>
>
>

-- 
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

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20200224/65f0dd08/attachment.html>