[Users] coordinate systems

[Erik Schnetter]

On Thu, Jul 19, 2012 at 11:21 AM, Ian Hinder <ian.hinder at aei.mpg.de> wrote:
>
> 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.

What I describe above uses CartGrid3D...

-erik

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