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@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
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