dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Wed, Apr 29, 2009 at 07:31:16AM -0500, Matthew Knepley wrote:
> 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

I care. It sure has a certain entertainment value. ;-)

-- 
Anders

Attachment: signature.asc
Description: Digital signature