On Tue, Apr 28, 2009 at 03:36:48PM -0500, Matthew Knepley wrote: > On Tue, Apr 28, 2009 at 3:32 PM, Anders Logg <[email protected]> wrote: > > On Tue, Apr 28, 2009 at 03:25:18PM -0500, Matthew Knepley wrote: > > On Tue, Apr 28, 2009 at 3:05 PM, Robert Kirby <[email protected]> > wrote: > > > > Hi all, > > it's my understanding that the way ufc ordering works is for > adjacent > cells > > to > > alternate orientation so that they traverse edges (and faces in 3d) > the > > same global > > way. It seems that in 2d this is equivalent to two-coloring a graph > (each > > cell is either > > clockwise or counterclockwise) > > > > Has there been any thought to issues at imposing ufc ordering in > parallel, > > where each > > process has to assign an orientation to the first local cell, and > different > > processors > > might disagree? > > > > > > How would this disagreement come about? Maybe I do not understand what > UFC is > > doing > > here is how I do it: > > > > 1) Values are associated with Sieve points. If there are multiple > values on > > an edge, these > > values are ordered here. > > > > 2) Every Sieve arrow has an orientation. This orientation produced by > a > > traversal concatenates > > these orientations, and is relative to orientation to the initial > > orientation in the Sieve. > > > > 3) I do not see the parallel problem because all data is just traded > between > > shared sieve > > points, and thus has identical orientations. However, I use the > > traversals to construct > > ordered arrays of data. Maybe UFC does something else. > > > > Matt > > With UFC, the orientation is never stored but implied by the vertices > of the entity, going from lower index to higher index. So an edge from > vertex 15 to 25 will be directed 15 --> 25 which means two cells > sharing a common edge from 15 to 25 will both assign the same > direction (since they have a common numbering for the vertices). > > > How does this work for higher dimensions? > > Matt
You mean faces on tets? Same thing there, we assign a unique orientation based on the vertices of the faces. Or do you mean higher dimension as in higher than R^3? Kent and I did this for arbitrary subsimplices in R^n in the Exterior Calculus package and it works there as well. In particular numbering entities based on a lexicographical ordering of their non-incident vertices. -- Anders
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