On the $q$-generalised multinomial/divergence correspondence
Keisuke Okamura
TL;DR
This work extends Wallis-type combinatorial asymptotics to a $q$-deformed multinomial PMF within Tsallis nonextensive statistics, showing that the leading term in the large-$n$ expansion is the Tsallis relative entropy $D_q(P||_0 Q)$. Higher-order corrections naturally generate a one-parameter family of lambda-extended divergences $D_q(P||_λ Q)$, with explicit recursivity and sign properties explored. The analysis combines $q$-algebra, analytic continuation of the Riemann zeta function, and a detailed examination of characteristic values and limits, unifying the combinatorial and information-theoretic perspectives across all real $q$. The results provide a new mathematical bridge between $q$-deformed combinatorics and nonextensive information geometry, with potential applications in statistical physics and information theory where Tsallis-type divergences are relevant.
Abstract
The asymptotic correspondence between the probability mass function of the $q$-deformed multinomial distribution and the $q$-generalised Kullback-Leibler divergence, also known as Tsallis relative entropy, is established. The probability mass function is generalised using the $q$-deformed algebra developed within the framework of nonextensive statistics, leading to the emergence of a family of divergence measures in the asymptotic limit as the system size increases. The coefficients in the asymptotic expansion yield Tsallis relative entropy as the leading-order term when $q$ is interpreted as an entropic parameter. Furthermore, higher-order expansion coefficients naturally introduce new divergence measures, extending Tsallis relative entropy through a one-parameter generalisation. Some fundamental properties of these extended divergences are also explored.
