[Dune-devel] YaspGrid becomes a tensor product grid

[Dominic Kempf]

Dear Dune Community,
I have spent the last weeks working on YaspGrid to make it a tensorproduct grid.
For those of you who dont know: A tensorproduct grid is a structured
axiparallel cube grid characterized by a coordinate vector for every
coordinate direction. In 2D two vectors x = {x_0,...,x_s(0)} and  y =
{y_0,...,y_s(1)} are given. The resulting grid is made of the
following vertices: { (x_i,y_j) | i=0..s(0), j=0..s(1)}. Such grids
are of great interest for quite a lot of people here in the Heidelberg
DUNE community. Workarounds based on UG and GeometryGrid have been
used that created gigantic overhead. After the release of SPGrid, Yasp
is no longer urgently needed and was thus recoded into a
tensorproductgrid.
Some remarks:
- In the backend (i.e. in the header /yaspgrid/grids.hh) the grids are
entirely characterized by their coordinate vectors.
- The code is completely backwards compatible. For all old
constructors, coordinate vectors are generated. Due to the relatively
low memory needs (in comparison to a DOF vector), this was chosen over
a specialization of the backend code for the equidistant case. Should
extensive performance testing show, that this is a problem, this will
be implemented.
- The data structure to be used to give coordinates to the constructor
of YaspGrid is Dune::array<std::vector<ctype>, dim>. Helper classes to
generate such vectors with sequences such as geometric series are to
follow, but not part of this first release.
- As a side effect, YaspGrid is no longer tied to having a trivial origin!
- While digging through the backend code, I realized a lot of
redundant code or code that is actually never used. Such things have
not been tackled yet.

Unfortunately implementation is not yet done completely. The following
features are NOT yet fully implemented:
- periodic grids
- the refinement option choosing to keep the overlap in cell size,
instead of physical size.

I invite everybody to take a look at my work and test it. You find the
feature branch on my github account:
https://github.com/dokempf/dune-grid/tree/feature/tensorproductgrid

I will not be available to work on this until around mid of november,
but until then, I would like to collect your feedback and wishes to
make the new YaspGrid first choice for problems that require a
tensorproduct grid.

Best regards,
Dominic Kempf