[Users] Assorted Parameter File Questions

[Gwyneth Allwright]

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
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