[Dune] globalRefine and ALUGRID_SIMPLEX

[Andreas Dedner]

Hi,
the grids will always be different.
DGF transforms cubes to simplicies by a dividing them into 6
tetrahedrons. Whereas globalrefine should actually divide each
each tetra! into 8 similar ones, e.g.,
your first DGF+globalrefine = 6*8=48 tetras
      second DGF             = 8*8=64 tetras
alu does not know that you started with cubes so it can not remove
the "make6" step, reine for cubes and then repeat the make6 algorithm
again.
Andreas

Dragan Vidovic wrote:
> Dear all,
> 
> I would like to draw your attention to the way the globalRefine
> function works with ALUGRID_SIMPLEX in 3d. I define a simple unit cube
> in a dgf file
> 
> DGF
> Interval
> 0 0 0  % first corner
> 1 1 1  % second corner
> 1 1 1  % 1 cells in x and 1 in y direction
> 
> and I do globalRefine(Dune::DGFGridInfo<GridType>::refineStepsForHalf())
> in the code. I would expect the result to be as if my dgf file was
> 
> DGF
> Interval
> 0 0 0  % first corner
> 1 1 1  % second corner
> 2 2 2  % 2 cells in x and 2 in y direction
> 
> but it is not. Actually, in the grid made by globalRefine, four cells
> stretch from the bottom to the top of the cube, which means that the
> new cells were not made by simply dividing the old cells into eight
> similar cells. This reduces the grid quality, and I believe it was not
> intended.
> 
> I must admit that my installation is somewhat older - I'm using a SVN
> version of Dune from 13. of November 2009, and Alugrid 1.1.14.
> 
> Cheers,
> 
> Dragan
> 
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