On the $Q$-polynomial property of the full bipartite graph of a Hamming graph

TL;DR

This paper proves that graphs derived from Hamming posets, viewed through their Hasse diagrams, possess the $Q$-polynomial property, extending previous results from attenuated space posets to a broader class.

Contribution

It establishes that graphs from Hamming posets are $Q$-polynomial, filling a gap in the understanding of $Q$-polynomial properties beyond distance-regular graphs.

Findings

Graphs from Hamming posets are $Q$-polynomial.

Extends $Q$-polynomial property to new classes of graphs.

Bridges gap between Hamming and attenuated space posets.

Abstract

The $Q$-polynomial property is an algebraic property of distance-regular graphs, that was introduced by Delsarte in his study of coding theory. Many distance-regular graphs admit the $Q$-polynomial property. Only recently the $Q$-polynomial property has been generalized to graphs that are not necessarily distance-regular. In [ J. Combin. Theory Ser. A, 205:105872, 2024 ], it was shown that graphs arising from the Hasse diagrams of the so-called attenuated space posets are $Q$-polynomial. These posets could be viewed as $q$-analogs of the Hamming posets, which were not studied in [ J. Combin. Theory Ser. A, 205:105872, 2024 ]. The main goal of this paper is to fill this gap by showing that the graphs arising from the Hasse diagrams of the Hamming posets are $Q$-polynomial.