[Gmsh] Mesh partition - point and line elements

[B. Lazarov]

On Friday 06 February 2009 20:34:29 sguzik at arrow.utias.utoronto.ca wrote:
> Quoting Umut Tabak <u.tabak at tudelft.nl>:
> > B. Lazarov wrote:
> >> Hello,
> >>
> >> I am trying to partion simple mesh using the partitioning libraries
> >> comming with GMSH. The partitioning is fine however if I define physical
> >> lines and physical points in the geo file,  in the resulting mesh file
> >> the line or the point element  belong to partition 0.  For surface
> >> elements the partitioning is done properly. Is it a bug? Or there is
> >> some other way around this behaviour.
> >>
> >> Best regards,
> >> Boyan
> >>
> >>
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> >
> > Developers will reply it better but as far as I read from the METIS
> > manual (which is the default graph partitioner in Gmsh), it can handle
> > quadrangles, triangles, hexahedra and tetrahedra so it works for these
> > elements. There are no algorithms for points and lines as I understand,
> > I have not read about Chaco partitioner though.
> >
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>
> Currently, Gmsh can only partition the highest-dimension elements in a
> mesh.  The partition information is then propagated to lower-dimension
> elements but only those on the extents of the mesh.  For
> lower-dimension elements in the interior, it is (possibly) ambiguous
> to which partition they belong so they are not labeled.
>
> It is entirely possible to add the lower-dimension elements to the
> partitioning graph -- however, I imagine this would also require
> weighting the elements, depending on what is needed.  This
> functionality is not currently implemented through the Gmsh interface
> but can be achieved by using Metis or Chaco directly.
>
> Boyan, you aren't the first to ask about partitioning lines and
> points.  If there is some consensus on the partitioning requirements,
> it probably can be implemented in Gmsh.  How would you need the lines
> and points partitioned relative to the surface elements?
>
> Stephen

I have separate implementation based on metis to partition everything. The 
partitioning is done on the nodal graph. One can mix all type of elements 
solid, surface, line and point elements for creating the nodal connectivity 
graph. Once the partitioning of the nodes is done , partitioning is performed 
over the elements based on the nodes. If an element has nodes which belong to 
domain 1 and some nodes which belong to domain 2 and so on, a decision  based 
on some rule can be made. The simplest rule would be that the element should 
belong to the domain with the smaller number of elements. 

Something similar can be implemented in GMSH. I really like the possibility to 
mesh and partion at the same time in the program. Doing it separately opens 
possibilities for more mistakes.  

Boyan



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