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Plane bipolar orientations and quadrant walks

Abstract : Bipolar orientations of planar maps have recently attracted some interest in combinatorics, probability theory and theoretical physics. Plane bipolar orientations with n edges are known to be counted by the nth Baxter number $b(n)$, which can be defined by a linear recurrence relation with polynomial coefficients. Equivalently, the associated generating function $\sum_n b(n) t^n$ is D-finite. In this paper, we address a much refined enumeration problem, where we record for every $r$ the number of faces of degree $r$. When these degrees are bounded, the associated generating function is given as the constant term of a multivariate rational series, and thus is still D-finite. We also provide detailed asymptotic estimates for the corresponding numbers. The methods used earlier to count all plane bipolar orientations, regardless of their face degrees, do not generalize easily to record face degrees. Instead, we start from a recent bijection, due to Kenyon et al., that sends bipolar orientations onto certain lattice walks confined to the first quadrant. Thanks to this bijection, the study of bipolar orientations meets the study of walks confined to a cone, which has been extremely active in the past 15 years. Some of our proofs rely on recent developments in this field, while others are purely bijective. Our asymptotic results also involve probabilistic arguments.
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Contributor : Mireille Bousquet-Mélou <>
Submitted on : Thursday, December 5, 2019 - 9:57:37 AM
Last modification on : Monday, December 14, 2020 - 5:26:20 PM
Long-term archiving on: : Friday, March 6, 2020 - 1:02:27 PM


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  • HAL Id : hal-02127624, version 1
  • ARXIV : 1905.04256


Mireille Bousquet-Mélou, Éric Fusy, Kilian Raschel. Plane bipolar orientations and quadrant walks. Seminaire Lotharingien de Combinatoire, Université Louis Pasteur, In press. ⟨hal-02127624⟩



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