Abstract
We give closed-form expressions for recently discovered invariants of Poncelet N-periodic trajectories in the elliptic billiard with spatial integrals evaluated over the boundary of the elliptic billiard. The integrand is weighed by a measure equal to the density of rays hitting a given boundary point. We find that aperiodic averages are smooth and monotonic on caustic eccentricity, and are consistent with the invariant values predicted at the discrete caustic parameters which admit a given N-periodic family. Our results are verified by numerical simulation.
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Notes
In our case, we find the caustic using an optimization procedure described in [18].
A billiard N-periodic is fully specified by its two integrals of motion, so any “new” invariants are ultimately dependent on basic conservations.
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Acknowledgements
We would like to thank Sergei Tabachnikov, Arseniy Akopyan, Hellmuth Stachel, and Sergey Galkin for invaluable discussions.
The second author is fellow of CNPq and coordinator of Project PRONEX/ CNPq/ FAPEG 2017 10 26 7000 508.
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Garcia, R., Koiller, J. & Reznik, D. Estimating Elliptic Billiard Invariants with Spatial Integrals. J Dyn Control Syst 29, 757–767 (2023). https://doi.org/10.1007/s10883-022-09608-y
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DOI: https://doi.org/10.1007/s10883-022-09608-y