Log-Concavity of Infinite Product Generating Functions

arXiv (Cornell University)

Abstract

In the $1970$s Nicolas proved that the coefficients $p_d(n)$ defined by the generating function \begin{equation*} \sum_{n=0}^{\infty} p_d(n) \, q^n = \prod_{n=1}^{\infty} \left( 1- q^n\right)^{-n^{d-1}} \end{equation*} are log-concave for $d=1$. Recently, Ono, Pujahari, and Rolen have extended the result to $d=2$. Note that $p_1(n)=p(n)$ is the partition function and $p_2(n)=\func{pp}\left( n\right) $ is the number of plane partitions. In this paper, we invest in properties for $p_d(n)$ for general $d$. Let $n \geq 6$. Then $p_d(n)$ is almost log-concave for $n$ divisible by $3$ and almost strictly log-convex otherwise.

Authors 1

1. Bernhard E. Heim Aachen Lehrstuhl A für Mathematik

   RWTH Aachen University · Kutaisi International University

   Affiliation as printed

   Kutaisi International University , 5/7 , Youth Avenue , Kutaisi , 4600 Georgia Lehrstuhl A für Mathematik ,

   Lehrstuhl A für Mathematik , RWTH Aachen University , 52056 Aachen , Germany