Unimodality of q-Fibonomial polynomials and related quotients

We prove that every q-Fibonomial polynomial is symmetric and unimodal, settling a conjecture of Bergeron, Ceballos, and Küstner. Its coefficients are strictly increasing in the first half whenever both parameters are at least 9. The proof expresses adjacent coefficient differences as a principal contribution governed by a convolution of interval indicators and a sum of contributions from other roots of unity. Fibonacci addition identities give a uniform lower bound for the former, while strong divisibility and root-of-unity moment estimates control the latter. For general quotients of q-integers with fixed denominators, we prove eventual unimodality under strict balance of the limiting numerator lengths and a pole multiplicity gap. We also establish a growth-rate obstruction for strong divisibility sequences, prove unimodality for strict divisibility chains, and classify the positive normalized coprime second-order recurrences whose quotients are unimodal for all parameters.

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Publication Details

Journal
Zenodo (CERN European Organization for Nuclear Research)
Published
2026-10-09
DOI
https://doi.org/10.5281/zenodo.23260784
Primary Topic
Advanced Combinatorial Mathematics
Type
preprint
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preprint

Unimodality of q-Fibonomial polynomials and related quotients

Shutao Jiang
Zenodo (CERN European Organization for Nuclear Research)
Advanced Combinatorial Mathematics
preprint

Unimodality of q-Fibonomial polynomials and related quotients

Shutao Jiang
preprint en

Abstract

We prove that every q-Fibonomial polynomial is symmetric and unimodal, settling a conjecture of Bergeron, Ceballos, and Küstner. Its coefficients are strictly increasing in the first half whenever both parameters are at least 9. The proof expresses adjacent coefficient differences as a principal contribution governed by a convolution of interval indicators and a sum of contributions from other roots of unity. Fibonacci addition identities give a uniform lower bound for the former, while strong divisibility and root-of-unity moment estimates control the latter. For general quotients of q-integers with fixed denominators, we prove eventual unimodality under strict balance of the limiting numerator lengths and a pole multiplicity gap. We also establish a growth-rate obstruction for strong divisibility sequences, prove unimodality for strict divisibility chains, and classify the positive normalized coprime second-order recurrences whose quotients are unimodal for all parameters.

Zenodo (CERN European Organization for Nuclear Research)
East China Normal University (CN)
Advanced Combinatorial Mathematics
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Unimodality of q-Fibonomial polynomials and related quotients — Shutao Jiang · Zenodo (CERN European Organization for Nuclear Research) (2026) | TGRS Research Map | TGRS