dolfin team mailing list archive

["Johan Hoffman" <jhoffman@xxxxxxxxxx>]

> On Tue, Dec 19, 2006 at 02:59:29PM +0100, Johan Hoffman wrote:
>> I am now working on mesh refinement/coarsening in Dolfin. There are 2
>> different approaches; either (1) we have one mesh object that we modify,
>> or (2) we have a hierarchy of meshes. I think we should support both (1)
>> and (2). The benefit of (1) is that it is simple and cheap to store,
>> whereas (2) can make coarsening simpler and is typically needed in
>> geometric multigrid.
>>
>> I plan to add a class MeshHierarchy for the purpose of (2). I want to
>> keep
>> it simple, but to minimize storage we need to be somewhat more clever
>> than
>> just using a simple array with meshes. I guess something like (i) a
>> primitive base mesh; mesh0, which is a regular mesh object, together
>> with
>> (ii) the number of refinement levels, and (iii) for each level k the
>> cells
>> that are part k but not k-1, together with their vertices and edges.
>
> Sounds good. The mesh class should support this without difficulty
> (storing a mesh that is not connected).

Good.

> The mapping from one level to the other can use the class MeshFunction
> in the same way that it is currently used to map entities on a
> boundary mesh to the original mesh.

Ok.

>> Is there any problem in considering (iii) to be some sort of "broken
>> mesh", and treat mesh_k as a regular mesh object that may not be
>> connected? If we do this then MeshHierarchy would basically just be a
>> collection of mesh objects, together with parent-child info.
>
> So the parent-child info could be a MeshFunction.
>
> I think there should also be some functionality for storing the entire
> hierarchy so that each mesh in the hierarchy is a complete
> representation. Maybe there could be a flag to choose how the
> hierarchy is stored?

Yes, we could do that. In either case one should be able to ask for mesh_k
and get a complete mesh object by assembling the "leaf cells" of meshes
m<k, with the leaf cells being cells without children.

/Johan






> /Anders
>
>
>> Any other ideas/comments/objections?
>>
>> /Johan
>
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