[Users] bug in Dissipation thorn?

Kentaro Takami kentaro.takami at aei.mpg.de
Fri Feb 22 11:38:41 CST 2013

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.

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:


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