2) What's going to happen with a 2 moving grids when apparent horizon was formed? Since I use maximum density tracking mechanism to track the positions of the NSs I want to switch the moving grids off after the formation of the apparent horizon and have only one centre of refinement at the origin.

This behavior is also not controlled by AHFinderDirect, but by CarpetRegrid2. The only way I know to trigger grid changes like you describe is to write your own thorn which inherits from CarpetRegrid2 and changes its variables num_levels[i] as desired. Perhaps someone else can give better advice here.

You do not need to switch off these additional grids, unless the
greatly enlarge the fine grid you are evolving. Carpet combines the
refined regions, and if you have three approximately equal regions,
the combined region will work just fine. Is there a particular reason
you want to switch them off?

I think the problem in his case is that the grids follow the position of the maximum of the density. What we do with Whisky simulations of NS-NS mergers is to stop the movement of the grids after the merger (so you will end up having a set of fine grids fixed where the BH will form). If you don't do that, after the collapse to BH the positions of the grids would be quite "random". For example, if you are left with a disk outside the BH, then the centers of the grids will follow the position of the maximum density in the disk, which is not what you want usually.

Cheers,
Bruno

Dr. Bruno Giacomazzo
JILA - University of Colorado
440 UCB
Boulder, CO 80309
USA

Tel.  : +1 303-492-5170
Fax  : +1 303-492-5235

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