[petsc-users] Understanding DMPlexDistribute overlap

[Francesco Caimmi]

Dear all, 

I was playing with DMPlex objects and I was trying to exactly figure out what 
the `overlap` parameter in DMPlexDistribute does.

From the tutorial "Flexible, Scalable Mesh and Data Management
using PETSc DMPlex" (slide 10) and from the work by Knepley et al. 
"Unstructured Overlapping Mesh Distribution in Parallel" I somehow got the 
idea that it should control the "depth" of the mesh overlap.
That is, given the partition boundary, if overlay is set to 0 only the 
entities adjacent (in the DMPlex topological sense and with the "style" defined 
by the AdjacencyUse routines) to entities at the boundary are shared, if 
overlay is 1 the first and the second neighbors (always in the DMPlex 
topological sense) are shared and so on, up to the point were we have a full 
duplicate of the mesh on each process (i.e. there is no upper bound on 
`overlap`).

Is this correct or am I -totally- misunderstanding the meaning of the 
parameter?

I am asking this because I see some behavior I cannot explain at varying the 
value of the overlap, but before going into the details I would like to be 
sure to understand  exactly what the overlap parameter is supposed to do.

Many thanks,
-- 
Francesco Caimmi
 
Laboratorio di Ingegneria dei Polimeri
http://www.chem.polimi.it/polyenglab/

Politecnico di Milano - Dipartimento di Chimica,
Materiali e Ingegneria Chimica “Giulio Natta”

P.zza Leonardo da Vinci, 32
I-20133 Milano
Tel. +39.02.2399.4711
Fax +39.02.7063.8173

francesco.caimmi at polimi.it
Skype: fmglcaimmi (please arrange meetings by e-mail)