dolfin team mailing list archive

[Matthew Knepley <knepley@xxxxxxxxx>]

On Wed, Apr 29, 2009 at 6:17 AM, Jed Brown <jed@xxxxxxxx> wrote:

> Matthew Knepley wrote:
>
> > I cannot be more emphatic here. <voice_of_god>THERE IS NO SPECIAL
> > CASING</voice_of_god>.  At all. In the whole thing. You can argue that
> > in some cases it might be slower, but it works for any arrangement in
> > any dimension. I will never put that special case crap in my
> > code. Ever.
>
> Voice of g-d or otherwise, the code disagrees.
>
> compute{Triangle,Quadrilateral,Tetrahedral,Hexahedral,LineFace}Geometry
> orientTriangle
>
> MeshInterpolatePoints - Assumes 3D and tetrahedron


Yep, it is geometric, not topological.


>
> Sieve/MeshSurgery.hh is all special-cased


Not mine.


>
> But the above is either necessary or superficial.  Now consider
> Selection::numFaceVertices which appears to require homogeneous topology
> and assume that all faces have the same topology.  Furthermore, if you
> want to support dim > 3 or more exotic polyhedrons, it is no longer the
> case that topological dimension and total number of vertices defines the
> element topology.
>
>      switch (cellDim) {
>      case 0 :
>        _numFaceVertices = 0;
>        break;
>      case 1 :
>        _numFaceVertices = 1;
>        break;
>      case 2:
>        switch (numCorners) {
>        case 3 : // triangle
>          _numFaceVertices = 2; // Edge has 2 vertices
>          break;
>        case 4 : // quadrilateral
>          _numFaceVertices = 2; // Edge has 2 vertices
>          break;
>        default :
>          throw ALE::Exception("Invalid number of face corners");
>        }
>        break;
>      case 3:
>        switch (numCorners)     {
>        case 4 : // tetradehdron
>          _numFaceVertices = 3; // Face has 3 vertices
>          break;
>        case 8 : // hexahedron
>          _numFaceVertices = 4; // Face has 4 vertices
>          break;
>        default :
>          throw ALE::Exception("Invalid number of face corners");
>        }
>        break;
>      default:
>        throw ALE::Exception("Invalid cell dimension");
>      }
>
>
> Selection::faceOrientation is the same pattern with a bunch more code
> (including another switch over orientation of each face of a hex, which
> can be replaced with an array describing the canonical orientation).
> The point is that this information needs to show up somewhere.  The MBCN
> convention allows it to show up in a couple of arrays defined in one
> place, *reducing* the number of places that you need to special-case.


None of which is necessary for this crap. That code is used to construct
fault
surfaces inside of a volume. I know how to do this topologically, but it
requires
a fully interpolated mesh. PyLith was unwilling to do this, so we had to
special
case since topology is thrown away.

The real way to solve this is to construct the intermediates on the fly, but
it takes
some real thinking to make this efficient, and I am only one person.


>
> This is drifting rather off-topic for Dolfin, especially since they only
> work with simplices anyway, so perhaps we should continue the discussion
> off-list.


I'm sure they care (a little).

  Matt


>
> Jed
>
>


-- 
What most experimenters take for granted before they begin their experiments
is infinitely more interesting than any results to which their experiments
lead.
-- Norbert Wiener