[petsc-users] partition of DM Vec entries

[Sang pham van]

Hi Barry,

Thank your for your answer. I am writing a parallel code for
smoothed-particle hydrodynamic, in this code I used a DMDA background mesh
for management of particles. Each DMDA cell manages a number of particles,
the number can change in both time and cell. In each time step, I need to
update position and velocity of particles in border cells to neighbor
partition. I think I can not use DMDA Vec to do this be cause the number of
particles is not the same in all ghost cells.

I think I am able to write a routine do this work, but the code may be
quite complicated and not so "formal", I would be very appreciated if you
can suggest a method to solve my problem.

Many thanks.




On Sat, Oct 15, 2016 at 9:40 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>   Thanks, the question is very clear now.
>
>   For DMDA you can use DMDAGetNeighborsRank() to get the list of the (up
> to) 9 neighbors of a processor. (Sadly this routine does not have a manual
> page but the arguments are obvious). For other DM I don't think there is
> any simple way to get this information. For none of the DM is there a way
> to get information about what process is providing a specific ghost cell.
>
>   It is the "hope" of PETSc (and I would think most parallel computing
> models) that the details of exactly what process is computing neighbor
> values should not matter for your own computation. Maybe if you provide
> more details on how you wish to use this information we may have
> suggestions on how to proceed.
>
>   Barry
>
>
>
> > On Oct 14, 2016, at 9:23 PM, Sang pham van <pvsang002 at gmail.com> wrote:
> >
> > Hi Barry,
> >
> > In 2 processes case, the problem is simple, as I know all ghost cells of
> partition 0 are updated from partition 1. However, in the case of many
> processes, how do I know from which partitions ghost cells of partition 0
> are updated? In other words, How can I know neighboring partitions of the
> partition 0? and can I get a list of ghost cells managing by a neighboring
> partition?
> > Please let me know if my question is still not clear.
> >
> > Many thanks.
> >
> >
> > On Sat, Oct 15, 2016 at 8:59 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> > > On Oct 14, 2016, at 8:50 PM, Sang pham van <pvsang002 at gmail.com>
> wrote:
> > >
> > > Hi,
> > >
> > > I am using DM Vec for a FV code, for some reasons, I want to know
> partition of all ghost cells of a specific partition. is there a way do
> that?
> >
> >   Could you please explain in more detail what you want, I don't
> understand? Perhaps give a specific example with 2 processes?
> >
> >  Barry
> >
> >
> >
> > >
> > > Many thanks.
> > >
> > > Best,
> > >
> >
> >
>
>
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