Got it.

I'm specifically thinking about this in terms of the gather stage of my PIC code, where I loop over local particles to fill local density and flux arrays by linearly interpolating particle positions to the grid. The gather function currently assumes that the coordinates (i.e., the array representation of DMSwarmPICField_coor) of all particles on a given rank would correspond to only the global indices owned by that rank, via the relationship between indices and coordinates in the associated cell DM. Based on what you described, it sounds like I need to make sure that I initially lay down the particles so that their rank matches their coordinates.

--Matt
==========================
Matthew Young, PhD (he/him)
Research Scientist II
Space Science Center
University of New Hampshire
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On Fri, May 12, 2023 at 5:15 AM Matthew Knepley <knepley@gmail.com> wrote:
On Thu, May 11, 2023 at 9:15 PM Matthew Young <myoung.space.science@gmail.com> wrote:
Does setting up a PIC-type DMSWARM with an associated cell DM guarantee that each MPI rank will own the particles with coordinates inside the bounds of the portion of the grid it owns?

There is a caveat that we are currently fixing. Swarm communication is setup to be nearest neighbor (since there is no coarse grid of bounding boxes). So if your particles are initially in the right place, and only move nearest neighbor, everything is fine. We are adding a hierarchy of bounding boxes so that we can communicate anywhere.

  Thanks,

      Matt
 
--Matt
==========================
Matthew Young, PhD (he/him)
Research Scientist II
Space Science Center
University of New Hampshire
==========================


--
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