[Carpet] refinement in space only

[Erik Schnetter]

On Jul 27, 2006, at 12:52:44, Yosef Zlochower wrote:

> Hi,
>
>    I am trying to use carpet to refine in space only. I used
> the parameters
>
>   time::dtfac                             = 0.03125
> Carpet::prolongation_order_space   = 5
> Carpet::prolongation_order_time    = 0
> Carpet::max_refinement_levels      = 5 #5
> Carpet::time_refinement_factors = "[1,1,1,1,1]"
> Carpet::num_integrator_substeps = 3
> Carpet::use_outer_buffer_zones = "yes"
> CarpetRegrid::refinement_levels    = 5 #5
> CarpetRegrid::regrid_every         = 0
> CarpetRegrid::refined_regions = "centre"
>
> Is this correct?

I see nothing obviously wrong with this.  Note that the CFL factor on  
the finest grid is 0.03125 * 2^(5-1) = 0.5; this may be too large  
depending on your setup.

> If not, what parameters should I set so that carpet
> refines in space only. I evolved my code with these parameters and it
> developed nans near the boundary of the finest level (both with and
> without Kreiss Oliger dissipation).

Try to find out what goes wrong before there are nans.  Are things  
set to zero instead of reasonable numbers?  Are there  
discontinuities?  High frequency noise?  You can run with a wave  
equation and compare to the exact solution or a unigrid run to  
debug.  I also find that two-level setups are much easier to debug  
than five-level setups.

> The reason why I
> wanted to refine in space only, was to that I wanted to calculate psi4
> and then decompose in l,m modes (and I wanted all these decompositions
> to be on the same time level). However, I found that carpet replaces
> all boundary and buffer points with zeros. What parameters should I
> set so that Carpet will interpolate the data from the coarse grids
> onto the finner grids for this type of analysis level gridfunction?

The way Carpet treats refinement boundaries depends on the number of  
time levels that a grid function has.  The rules for this are a bit  
arcane for backward compatibility.  I suggest that you set the group  
tag "Prolongation" to what you desire, as in

CCTK_REAL X type=GF TAGS='Prolongation="Lagrange"'

and ensure that this grid function has permanent storage.

-erik

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

My email is as private as my paper mail.  I therefore support encrypting
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