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<p>Dear Yuhua,<br>
<br>
Thank you for writing and for putting the code and the<br>
paper draft in a public repository under GPLv2+. Independent<br>
contributions of this kind are welcome, and a<br>
test-particle geodesic tracker is something we don't have: the ET
currently ships<br>
fluid tracers (particle_tracerET) and puncture tracking<br>
(PunctureTracker), but not a timelike geodesic integrator on the
3+1<br>
metric.<br>
<br>
Were you hoping to have it included in the ET, or were you just
looking<br>
to share the code with the community? If so, we can help you with
the process.<br>
Please take a look at <a class="moz-txt-link-freetext" href="https://einsteintoolkit.org/contribute.html">https://einsteintoolkit.org/contribute.html</a><br>
if you haven't already.<br>
<br>
If you would like to do something less formal, we can share<br>
your link on our list of "thorns we know of":<br>
<a class="moz-txt-link-freetext" href="https://docs.einsteintoolkit.org/et-docs/Thorns_we_know_of">https://docs.einsteintoolkit.org/et-docs/Thorns_we_know_of</a><br>
<br>
Best regards,<br>
<br>
Steven R. Brandt<br>
<br>
</p>
<div class="moz-cite-prefix">On 9/8/2026 12:28 AM, Yuhua Li via
Users wrote:<br>
</div>
<blockquote type="cite"
cite="mid:74f2c974.b12.1a07f7ce0ce.Coremail.liyhts@yeah.net">
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style="line-height:1.7;color:#000000;font-size:14px;font-family:Arial">
<div style="margin:0;">Dear Einstein Toolkit community,</div>
<div style="margin:0;"><br>
</div>
<div style="margin:0;">I am a retired researcher (background in
mathematics and computer science)</div>
<div style="margin:0;">working independently from China. Over
the past ten years I have been</div>
<div style="margin:0;">building a test-particle geodesic tracker
for the Einstein Toolkit, and I</div>
<div style="margin:0;">would like to share it with the
community.</div>
<div style="margin:0;"><br>
</div>
<div style="margin:0;">The Geodesic thorn integrates geodesics
for large numbers of test particles</div>
<div style="margin:0;">in Kerr–Schild Cartesian coordinates. It
supports (i) the exact Kerr–Schild</div>
<div style="margin:0;">metric, independent of the grid (verified
symbolically to be the vacuum</div>
<div style="margin:0;">solution to machine precision), and (ii)
27-point local Lagrange</div>
<div style="margin:0;">interpolation of the grid metric, so it
also works for arbitrary spacetimes</div>
<div style="margin:0;">carried on the grid (e.g., GRHydro
evolutions). The per-particle integration</div>
<div style="margin:0;">is fully independent and parallelized
with OpenMP (validated with 10^4</div>
<div style="margin:0;">particles).</div>
<div style="margin:0;"><br>
</div>
<div style="margin:0;">The code (GPLv2+), the configuration
files used in the validation runs, and a</div>
<div style="margin:0;">paper draft describing the method and
verification are all available in this</div>
<div style="margin:0;">public repository:
<a class="moz-txt-link-freetext" href="https://github.com/wylyhzh/Geodesic">https://github.com/wylyhzh/Geodesic</a></div>
<div style="margin:0;"><br>
</div>
<div style="margin:0;">I plan to submit the paper to arXiv
(gr-qc, cross-list astro-ph.HE) once it</div>
<div style="margin:0;">has benefited from the community's
feedback.</div>
<div style="margin:0;"><br>
</div>
<div style="margin:0;">I would appreciate: (1) feedback on
whether the thorn meets ET</div>
<div style="margin:0;">standards, and what would be needed to
have it listed with the ET thorns;</div>
<div style="margin:0;">(2) any comments on the paper. I am most
comfortable discussing in</div>
<div style="margin:0;">writing, so I would prefer to continue
the conversation here on the</div>
<div style="margin:0;">mailing list or by email, whichever is
more convenient.</div>
<div style="margin:0;"><br>
</div>
<div style="margin:0;">I am happy to provide any further
information.</div>
<div style="margin:0;"><br>
</div>
<div style="margin:0;">Best regards,</div>
<div style="margin:0;"><br>
</div>
<div style="margin:0;">Yuhua Li</div>
</div>
<br>
<fieldset class="moz-mime-attachment-header"></fieldset>
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