| Citation: | Wanjia Gong. A PERIODICITY DEGREE FOR TIME-T MAPS: DETECTION AND A POSTERIORI CERTIFICATION OF PERIODIC ORBITS[J]. Journal of Applied Analysis & Computation, 2026, 16(5): 2515-2539. doi: 10.11948/20260026 |
We develop a scalar interface between numerical detection and a posteriori certification of T-periodic solutions in time-periodic ODEs. Starting from the time-T map, we introduce the periodicity degree, a bounded indicator of one-period recurrence, and establish its basic analytical properties on compact sets. The periodicity degree serves as an optimization-friendly detector of near-fixed points of the time-T map. To convert such numerical evidence into a mathematically valid existence statement, we provide a contraction-based a posteriori criterion that upgrades a detected near-fixed point to the existence of an exact fixed point with an explicit error bound. Numerical illustrations for two forced benchmarks clarify the distinction between detection and certification, while a Lorenz double-scroll example shows how recurrence-guided lag selection and local Poincaré/Newton refinement can be combined to obtain and interpret a high-accuracy periodic-orbit candidate in a chaotic regime.
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Benchmark Ⅰ. Filled markers indicate
Benchmark Ⅰ. Local landscape of
Time evolution of
Benchmark Ⅱ on the cylinder
Benchmark Ⅱ: Time evolution of
Two-pass lag selection for the Lorenz trajectory on
Lag-driven event selection and Newton–Poincaré refinement on the section
Phase-dependent continuous-time closure defect over one refined period. The curve shows
Lorenz attractor together with the refined periodic-orbit candidate
Periodicity-degree signal evaluated at the refined period