[Users] coordinate systems

[Ian Hinder]

On 19 Jul 2012, at 11:19, Erik Schnetter wrote:

> 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.

I think that CoordBase does not support anything other than CartGrid3D, so you won't be able to use any thorn which uses CoordBase.

-- 
Ian Hinder
http://numrel.aei.mpg.de/people/hinder