[Users] coordinate systems

[Erik Schnetter]

Comer

Do you intend to use existing thorns to evolve e.g. the Einstein
equations, or do you plan to write your own thorns?

If you use existing thorns: As written, they will not be able to
handle the coordinate singularities on the axes. Instead, we use
multi-block methods.

If you write your own thorns: Since you will be implementing your own
differencing methods, the Cactus coordinates are basically only needed
to label grid point. CartGrid3D can handle this; e.g. spherical or
cylindrical coordinate systems are orthogonal. You will only need to
correctly specify the respective coordinate ranges (e.g. using
[0,rmax] for r and [0,2pi] for phi) in your parameter file. The
unification of f(phi=0) and f(phi=2pi) would be handled via a
periodicity condition, which is provided e.g. by thorn Periodic.

What remains is that Cactus labels the coordinates x,y,z instead of
r,z,phi... but this is mainly a small inconvenience. Altogether, it is
straightforward to use spherical or cylindrical coordinates with
existing thorns, and we therefore never bothered to implement any new
coordinate systems for this.

-erik

On Wed, Jul 18, 2012 at 3:42 PM, Ian Hinder <ian.hinder at aei.mpg.de> wrote:
>
> On 18 Jul 2012, at 15:57, Comer Duncan wrote:
>
> Hi,
>
> I am wondering exactly which (common) coordinate systems are 'deeply'
> supported in Cactus?  These days of course most use Cartesians.  I think I
> see reference to spher3D in various places but am not certain the extent to
> which spherical coords are fully supported.  Also, I see no mention to
> cylindrical coordinates.  So, I am asking for guidance about just what is
> the breadth of common 3D coordinate system support.  Can you please let me
> know?
>
> Thanks very much.
>
>
> I believe that for anything nontrivial, only 3D Cartesian coordinates can be
> used.
>
> --
> Ian Hinder
> http://numrel.aei.mpg.de/people/hinder
>
>
> _______________________________________________
> Users mailing list
> Users at einsteintoolkit.org
> http://lists.einsteintoolkit.org/mailman/listinfo/users
>



-- 
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/