[Users] coupling Llama to an evolution code

Haas, Roland rhaas at illinois.edu
Thu May 16 08:30:04 CDT 2019

Hello Ian, Miguel,

using CartesianCoordinates is almost the same as using Coordinates with
its (default) "cartesian" patch. Only almost b/c of two things:

* CartesianCoordinates does not provide the function
  MultiPatch_GetDomainSpecification and the others that Coordinates
  provides (eg MultiPatch_GetBoundarySpecification)
* Coordinates has parameters ncells_[xyz] and patch_[xyz]{min,max} that
  describe its single Cartesian patch (used by
  MultiPatch_GetDomainSpecification) Yours,

so basically CartesianCoordinates provides the grid functions to make
typical science codes work but not enough to make eg CartGrid3D's
CartGrid3D::type = "multipatch" or Carpet::domain_from_multipatch work.

One could almost use Coordinates with its default values for ncells and
the patch sizes as a replacement for CartesianCoords since the values
of the missing parameters are only accessible via the aliased functions
that CartesianCoordinates is missing. 

However Carpet currently torpedoes any such attempt since it requires
that the aliased function "MultiPatch_GetDomainSpecification" is
missing unless Carpet::domain_from_multipatch is set. Further
CarpetRegrid2 and CarpetMask will use MultiPatch_XXX if it exists
obtaining incorrect results.

The only reason CartesianCoordinates was not proposed for the ET was
that Llama itself was included so at that point the idea was that one
could use Coordinates with its "cartesian" patch type for these cases.
However as outlined in the paragraph above that is only almost true.


> On 10 May 2019, at 10:22, Miguel Zilhão <miguel.zilhao.nogueira at tecnico.ulisboa.pt<mailto:miguel.zilhao.nogueira at tecnico.ulisboa.pt>> wrote:
> hi Ian,
> yes, i guess the CartesianCoordinate thorn could work. this is not part of the ET, though, is it?
> Hi Miguel,
> You're right; I hadn't realised this.  It's in the CTGamma arrangement:
> https://bitbucket.org/llamacode/ctgamma/src/master/
> but is not part of the toolkit. Just clone CTGamma into arrangements and add CTGamma/CartesianCoordinates to the thornlist and recompile.
> --
> Ian Hinder
> Research Software Engineer
> University of Manchester, UK

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