Abelian groups are polynomially stable

Abstract

In recent years, there has been a considerable amount of interest in stability of equations and their corresponding groups. Here, we initiate the systematic study of the quantitative aspect of this theory. We develop a novel method, inspired by the Ornstein-Weiss quasi-tiling technique, to prove that abelian groups are polynomially stable with respect to permutations, under the normalized Hamming metrics on the groups $\mathrm{Sym}(n)$. In particular, this means that there exists $D\ge 1$ such that for $A,B\in \mathrm{Sym}(n)$, if $AB$ is $\delta$-close to $BA$, then $A$ and $B$ are $\epsilon$-close to a commuting pair of permutations, where $\epsilon \le O({\delta }^{1/D})$. We also observe a property-testing reformulation of this result, yielding efficient testers for certain permutation properties.

49 pages