[Carpet] gf contamination

[Yosef Zlochower]

Erik Schnetter wrote:
> On Aug 3, 2006, at 19:30:20, Yosef Zlochower wrote:
>
>> Hi,
>>
>>    I am having some difficulty when evolving my code with carpet.  I am
>> attempting to evolve my code with prolongation in space only.  To
>> better understand the problem I set up my code so that the RHS were
>> all filled with 1.0e4 prior to calculating them.
>
> Carpet has a feature called "poisoning".  Carpet can fill all 
> uninitialised grid variables with a poison value (e.g. nan).  This 
> detects uninitialised values quite effectively.
>
>> My code then fills in
>> the RHS for all points on the grid except those on the three
>> gridplanes closest to the boundary (i.e. for (i=3; i<cctk_lsh[0]-3;
>> i++) etc ). In MoL_PostStep I first synchronize all the evolved fields
>> (but not the RHS)
>
> Correct; in MoL_PostStep, the RHS has already been used and will be 
> ignored.
>
>> and then alter the values of \tilde g_{ij} and
>> \tilde A_{ij} so that the algebraic constraints are enforced.
>
> Are you sure that this is the order in which you are doing things?  
> Can you show us the relevant part of your schedule.ccl?
>
I attached the relevant section of the schedule.ccl file.
>> I am
>> working on a problem where gxy = 0. However, I found that after 1
>> timestep the value of gxy 1 point in from the buffer zones
>
> If you do not use time interpolation then you do not need buffer 
> zones.  To simplify things, try switching them off completely.
>
>> is
>> non-zero, and grows when I increase the initial value of the RHS to
>> 1.0e5. So it looks like some junk from the buffer zones has leaked
>> into the evolved fields.
>
> I think you mean ghost zones.  The ghost zones are the outermost 3 
> grid points, which are filled through interpolation.
No. It was 17 point in so it was just inside of the buffer points.
I tried removing the buffer and got the same results (but this time the
bad value was just inside the ghostzones).
>
>> Here is the relevant segment of my parfile please note that my code
>> only needs 3 ghostzones but I choose 4. I also set
>> num_integrator_substeps = 4 even though 3 would be sufficient.
>
> This is also only needed for buffer zones.  Without buffer zones this 
> parameter is irrelevant.
>
>> (setting it back to 3 does not remove the problem)
>
>>
>>
>> driver::ghost_size = 4
>> mol::ode_method                        = "RK3"
>> driver::global_nx                       = 81 #51 #227 #259
>> driver::global_ny                       = 81 #51 #227 #259
>> driver::global_nz                       = 81 #51 #116 #132
>> grid::dxyz                              = .25
>> grid::domain                            = "full"
>>
>> time::dtfac                             = 0.125
>> #Carpet::prolongation_order_space   = 7
>> Carpet::prolongation_order_space   = 1
>> Carpet::prolongation_order_time    = 0
>> Carpet::max_refinement_levels      = 3 #5
>> #Carpet::buffer_width               = 0
>> Carpet::time_refinement_factors = "[1,1,1]"
>> Carpet::num_integrator_substeps = 4
>> Carpet::use_outer_buffer_zones = "yes"
>> #Carpet::init_each_timelevel = "yes"
>>
>> CarpetRegrid::refinement_levels    = 3 #5
>> CarpetRegrid::regrid_every         = 0
>> CarpetRegrid::refined_regions = "centre"
>>
>> Is there something obviously wrong in the parfile?
>
> Only the fact that you use buffer zones although you do not need 
> them.  Maybe there is a problem, since you also use uncommon temporal 
> and spatial interpolation orders.
>
>> I examined gxy on the y axis and found that after the first time step
>> gxy on level 0 is zero except at y=+-5 and +-2.5 On level 1 gxy has
>> the same behavior but is also non-zero at the points directly above
>> and below +-5. On the finest level gxy is non-zero on +-2.5 and +-
>> 2.4375.
>
> -erik
>
> --Erik Schnetter <schnetter at cct.lsu.edu>
>
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>
>
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