This sounds great.
> On Oct 15, 2016, at 12:17 AM, Dave May <[email protected]> wrote:
>
>
>
> On Saturday, 15 October 2016, Barry Smith <[email protected]> wrote:
>
> Unless the particles are more or less equally distributed over the the
> entire domain any kind of "domain decomposition" approach is questionably for
> managing the particles. Otherwise certain processes that have domains that
> contain most of the particles will have a great deal of work, for all of its
> particles, while domains with few particles will have little work. I can see
> two approaches to alleviate this problem.
>
> 1) constantly adjust the sizes/locations of the domains to load balance the
> particles per domain or
>
> 2) parallelize the particles (some how) instead of just the geometry.
>
> Anyways, there is a preliminary DMSWARM class in the development version of
> PETSc for helping to work with particles provided by Dave May. You might look
> at it. I don't know if it would useful for you or not. IMHO software library
> support for particle methods is still very primitive compared to finite
> difference/element support, in other words we still have a lot to do.
>
> If you are using an SPH formulation with a constant smoothing length (such as
> for incompressible media), then DMSWARM will be extremely useful. It manages
> the assignment of fields on point clouds and managed data exchanges required
> for particle advection and gather operations from neighbor cells required for
> evaluating the SPH basis functions.
>
> DMSWARM is in the master branch. We would be happy if you want to be beta
> tester. The API is in its infancy and thus having a user play with what's
> there would be the best way to refine the design as required.
>
> Take a look at the examples and let us know if you need help.
>
> Thanks,
> Dave
>
>
>
> Barry
>
>
>
>
>
> > On Oct 14, 2016, at 9:54 PM, Sang pham van <[email protected]> wrote:
> >
> > 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 <[email protected]> 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 <[email protected]> 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 <[email protected]> wrote:
> > >
> > > > On Oct 14, 2016, at 8:50 PM, Sang pham van <[email protected]> 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,
> > > >
> > >
> > >
> >
> >
