dolfin team mailing list archive

[Jed Brown <jed@xxxxxxxx>]

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

Sieve/MeshSurgery.hh is all special-cased


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.



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.

Jed

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