[Carpet] Tracking the puncture with Carpet

[Erik Schnetter]

On Jul 21, 2006, at 10:03:19, Yosef Zlochower wrote:

> Hi,
>
>    I am now wondering if it is indeed possible to evolve the puncture
> locations with MoL. Suppose that my routine to calculate the rhs
> of the puncture location has the following logic:
>
>    for all tracked punctures
>    {
>      If (on the right time level && on the right component) then
>         interpolate beta
>         p_loc_dot = - beta
>       else
>         p_loc_dot = 0
>    }
>
> First, will  all processors get the correct vale of p_loc_dot, or
> will only those processors that own a chunk of the correct level.
> It seems to me that if I set the time derivative of the puncture
> locations to zero at all the coarse levels and on the finest level,
> at all the wrong components, then MoL will only change the value
> of the puncture location on the right level and component.
> I am assuming that Carpet and MoL have the following evolution
> scheme
>
>    For all levels
>      for all components
>         for all MoL ministeps
>           call RHS
>       }
>     }

If I think correctly, then this scheme requires that you have a  
different puncture locations for the different levels, the same way  
the data themselves are evolved separately on different levels.   
After each coarse grid time step, you would have to overwrite the  
coarse information with the corresponding finer information in the  
same way the coarse grid data are overwritten by the fine grid data.

There is currently no mechanism in Cactus or Carpet for that.  I  
suggest that you evolve the puncture location on the fine grid only.   
If I see correctly, then this does not work with MoL, which currently  
supports grid arrays only when there is no mesh refinement.  (One  
would have to split out the time evolution routines for grid arrays  
and evolve them in global mode, keeping the current time correct.)   
However, since evolving grid functions and grid arrays together has  
such a complicated interplay, people tend to not do it, which is why  
no one has implemented it so far.

Solutions could be evolving the puncture location yourself in a home- 
grown time integrator, or determining the puncture location by a  
different means than integrating it in time.

-erik

-- 
Erik Schnetter <schnetter at cct.lsu.edu>

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