Hi All,
I have a bunch of overdue questions about parameter files that I've been meaning to ask. I'd be really grateful for any help. Also, if resources that address these questions already exist somewhere, please let me know!
1. I've seen ML_Ham and ML_mom from both ML_ADMConstraints and ML_BSSN requested as output in parameter files. Is there a difference?
2. IOScalar, IOBasic and IOASCII all seem to be able to produce 0D output, yet I've often seen all three used in the same parameter file. Is there a reason for this?
3. The following lines are from the example BBH parameter file ( https://einsteintoolkit.org/gallery/bbh/GW150914.rpar):
# Drop order instead of using upwinded stencils, only for advection derivatives SummationByParts::sbp_upwind_deriv = no SummationByParts::sbp_1st_deriv = yes SummationByParts::sbp_2nd_deriv = no
I don't have a very good understanding of what's being done here, but it seems as if we don't require the upwind and second derivative operators to satisfy summation by parts, so they're implemented by a different thorn? (Perhaps instead by GlobalDerivative?)
4. With the ADMMass thorn, one has to exclude the interiors of the compact objects. The documentation mentions using OutsideMask for this, but I can't find such a thorn. I also haven't been able to find a parameter file that uses ADMMass, but I've seen SpaceMask and CarpetMask used for other purposes, as well as the parameter: AHFinderDirect::set_mask_for_individual_horizon. I'm curious about how these different masking approaches work, and which is preferable.
5. Does calculating the ADM mass using QLM also require excluding the interiors of the objects?
6. For stable evolution on Cartesian grids, we need to halve the CFL factor on the outermost grid by setting Carpet::time_refinement_factors [1,1,...]. However, this isn't done for the example BNS parameter file ( https://einsteintoolkit.org/gallery/bns/nsnstohmns.par). Is it specific to BBHs?
Sorry for the many questions! If it would be easier to address them during one of the calls, I'll probably be able to make next Monday...
Gwyneth