On 15 May 2014 15:03, Garth N. Wells <gn...@cam.ac.uk> wrote: > > > On Thu, 15 May, 2014 at 2:43 PM, David Ham <david....@imperial.ac.uk> > wrote: > > Hi Chris, > > > > In Firedrake we solve this problem by imposing an additional > > constraint on numbering of entities (and DoFs) such that ghost > > entitites (which we call halo entities) are numbered after the owned > > ones. > > > Yes, this is the natural thing to do. DOLFIN already does this for dofs > (this will be more apparent in the upcoming switch to local dof > indexing). > > > This imposes a slightly suboptimal traversal order, since you are > > constraining RCM or SFC or whatever order you were using, but it > > means you can traverse owned cells and/or halo cells as contiguous > > blocks. (In fact we do a more complex version of this where we > > distinguish between owned cells which can't see the boundary and > > owned cells which can, but the principle is the same). > > I wouldn't expect this sub-optimal ordering to have a noticeable impact > on performance. > > I agree. We haven't noticed a problem.
David > Garth > > > Cheers, > > > > David > > > > > > On 15 May 2014 14:26, Chris Richardson <ch...@bpi.cam.ac.uk> wrote: > >> > >> Dear all, > >> > >> I am trying to integrate some changes for "ghost mesh" creation into > >> dolfin. > >> This involves adding some extra cells to the local mesh on each > >> process, > >> which overlap with neighbouring processes. > >> > >> That much is fine, but in order not to break user code, I was > >> thinking > >> that > >> the MeshEntityIterator should not by default iterate over these > >> "ghost > >> cells" or their any of their associated facets, edges and vertices, > >> unless they are shared with other "real" cells. > >> > >> However, skipping over them without reducing memory or CPU efficiency > >> could be tricky. Does anyone have any ideas? Or should it just be > >> left > >> up to users to sort out (i.e. just provide a way of flagging up if > >> you > >> are on a ghost cell). > >> > >> Chris > >> _______________________________________________ > >> fenics mailing list > >> fenics@fenicsproject.org > >> http://fenicsproject.org/mailman/listinfo/fenics > > > > > > > > -- > > Dr David Ham > > Departments of Mathematics and Computing > > Imperial College London > > > > http://www.imperial.ac.uk/people/david.ham > > -- Dr David Ham Departments of Mathematics and Computing Imperial College London http://www.imperial.ac.uk/people/david.ham
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