Periodic oscillation conjecture for combinatorial classes with evenly spaced dominant singularities

Let C\mathcal{C} be a combinatorial class with generating function fC(z)f_\mathcal{C}(z) of radius of convergence ρ<1\rho<1, and suppose

fC(z)=g(z)+h(z)(1z/ρ)α.f_\mathcal{C}(z)=g(z)+\frac{h(z)}{(1-z/\rho)^\alpha}.

Assume αN\alpha\notin-\mathbb{N}, and that gg and hh are analytic on the cut disk D(0,ρ)R0\overline{D}(0,\rho)\setminus\mathbb{R}^{\leqslant0}. If the only singularities on the line of convergence of the Dirichlet generating function FC(s)F_\mathcal{C}(s) are evenly spaced at

log(1/ρ)+2πiZ/ω\log(1/\rho)+2\pi i\mathbb{Z}/\omega

for some constant ω\omega, then the periodic oscillation conjecture asserts that

Cxc(x)ρxxα1,|\mathcal{C}_{\leqslant x}|\sim c(x)\rho^{-x}x^{\alpha-1},

where c(x)c(x) is a bounded function that oscillates with period ω\omega. Classes with irrational object sizes can exhibit such noncontinuous periodic fluctuations, while the conjecture predicts the corresponding asymptotic form under the stated analytic and singularity hypotheses.

Sources & referencesView supporting material

Primary source

David Bevan and Julien Condé, “Introducing irrational enumeration: analytic combinatorics for objects of irrational size”, arXiv:2412.14682 (2025).

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