[Users] New thorn proposal: Geodesic — test-particle geodesic tracking for the Einstein Toolkit

[Yuhua Li]

Dear Einstein Toolkit community,


I am a retired researcher (background in mathematics and computer science)
working independently from China. Over the past ten years I have been
building a test-particle geodesic tracker for the Einstein Toolkit, and I
would like to share it with the community.


The Geodesic thorn integrates geodesics for large numbers of test particles
in Kerr–Schild Cartesian coordinates. It supports (i) the exact Kerr–Schild
metric, independent of the grid (verified symbolically to be the vacuum
solution to machine precision), and (ii) 27-point local Lagrange
interpolation of the grid metric, so it also works for arbitrary spacetimes
carried on the grid (e.g., GRHydro evolutions). The per-particle integration
is fully independent and parallelized with OpenMP (validated with 10^4
particles).


The code (GPLv2+), the configuration files used in the validation runs, and a
paper draft describing the method and verification are all available in this
public repository: https://github.com/wylyhzh/Geodesic


I plan to submit the paper to arXiv (gr-qc, cross-list astro-ph.HE) once it
has benefited from the community's feedback.


I would appreciate: (1) feedback on whether the thorn meets ET
standards, and what would be needed to have it listed with the ET thorns;
(2) any comments on the paper. I am most comfortable discussing in
writing, so I would prefer to continue the conversation here on the
mailing list or by email, whichever is more convenient.


I am happy to provide any further information.


Best regards,


Yuhua Li
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