Connecting the q-Multiplicative Convolution and the Finite Difference Convolution

TL;DR

This paper proves a conjecture that a polynomial convolution operator preserves root mesh properties by establishing a connection between additive and multiplicative convolutions and adapting existing proofs.

Contribution

It introduces a novel link between Walsh and Grace-Szeg"o convolutions and applies it to prove root mesh preservation for a specific polynomial convolution.

Findings

Proved the root mesh preservation conjecture for the polynomial convolution.

Established a new connection between additive and multiplicative convolutions.

Streamlined and adapted existing proofs for the additive case.

Abstract

In a recent paper, Br\"and\'en, Krasikov, and Shapiro consider root location preservation properties of finite difference operators. To this end, the authors describe a natural polynomial convolution operator and conjecture that it preserves root mesh properties. We prove this conjecture using two methods. The first develops a novel connection between the additive (Walsh) and multiplicative (Grace-Szeg\"o) convolutions, which can be generically used to transfer results from multiplicative to additive. We then use this to transfer an analogous result, due to Lamprecht, which demonstrates logarithmic root mesh preservation properties of a certain $q$-multiplicative convolution operator. The second method proves the result directly using a modification of Lamprecht's proof of the logarithmic root mesh result. We present his original argument in a streamlined fashion and then make the appropriate alterations to apply it to the additive case.