[Users] bug in Dissipation thorn?

[Ian Hinder]

On 22 Feb 2013, at 18:38, Kentaro Takami <kentaro.takami at aei.mpg.de> wrote:

> First of all, I should give you more information.
> 
> In my test, I don't use OpenMP. So I use only MPI.
> I put dissipation only for spacetime variable such as gij, kij and so on.
> I check these difference for GF in checkpoint files.
> The difference appear from 2nd step of RK at 1st iteration,
> where the difference are for last a few digit, but grow up as
> increasing iterations.
> 
> In the following case we don't see difference.
> *don't activate Dissipation thorn.
> *using only 1 refinement level.
> *using certain special dx=dy=dz.
> 
> Further strange behavior:
> When I insert non-essential line such as "WRITE(*,*)" statement
> in "apply_dissipation.F77", sometimes the difference is disappeared.
> So, I doubted incorrect pointer position.

Are you using sufficient ghost zones?  

> 
> 
> Hi, Frank,
> 
>>> Finally I'm doubting the origin of the problem is "CactusNumerical/Dissipation",
>>> because when I don't activate this thorn, the problem can be disappeared.
>> 
>> This is interesting. So, you say you don't see random changes when
>> Dissipation isn't active, but you do when you activate it, and
>> everything else is the same? Which variables do you apply dissipation
>> to?
> 
> Yes, if we don't use Dissipation, HDF5 checkpoint files can become exactly same,
> at least my test case.
> I added dissipation for the following variables:
>        ML_BSSN::ML_log_confac
>        ML_BSSN::ML_metric
>        ML_BSSN::ML_trace_curv
>        ML_BSSN::ML_curv
>        ML_BSSN::ML_Gamma
>        ML_BSSN::ML_lapse
>        ML_BSSN::ML_shift
>        ML_BSSN::ML_dtlapse
>        ML_BSSN::ML_dtshift
> 
> 
> Kentaro
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-- 
Ian Hinder
http://numrel.aei.mpg.de/people/hinder

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