[Users] Geodesic: aei sampler on GW150914 (BBH AMR) -- verified reproducible (this week's users call)

[Yuhua Li]

Dear all,


Following my previous updates, I would like to report progress on applying
the samplers to the GW150914 binary-black-hole (BBH) spacetime on a 3-
level Carpet AMR mesh -- the first fully realistic (non-stationary) test
case for the geodesic probe.


Completed this week: the aei sampler (metric_interp=aei, time_interp=
linear). The 100-particle geodesic run at 256 resolution reproduces the
reference run exactly: all compared steps (t = 0 .. 0.3356, 40 particle
blocks of 100) agree to full double precision, with 0 dropped particles and
0 NaNs. At 128 resolution the t=0 block likewise matches a 2048 reference to
full precision, and the residual difference at t=0.2753 (position ~5e-4) is
consistent with the expected convergence of the sampler. In short, aei on
the GW150914 AMR evolution is now verified and reproducible.


Still under test (no result this week): the remaining samplers (local27 and
its time-linear variant l27lin, plus carpet) on the BBH AMR mesh. In
particular l27lin shows particle loss in the strong-curvature region near
the horizons; I am debugging the metric/Christoffel sampling path there. I
have no conclusion to report on them yet.


So this week's deliverable is a single, clean result: aei on GW150914 is
verified reproducible. The other samplers on the BBH AMR remain under
verification, and I will report a concrete result once they pass.


As before, I am most comfortable continuing in writing. Any questions or
suggestions on the strong-curvature path are welcome.


Best regards,
Yuhua Li
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