Sublinear Time Algorithms for Abelian Group Property Testing

In this paper, we study the problems of abelian group property testing in two models. In the partially specified model (PS-model), the algorithm does not know the group size but can access randomly chosen elements of the group, along with the Cayley table of these elements, which provides the result of the binary operation for every pair of selected elements. In the stronger fully specified model (FS-model), the algorithm knows the size of the group and has access to all its elements and the Cayley table. In property testing of abelian group property, given a finite set $G$ and oracle access to a binary operation $*:G^2\to G$, we aim to distinguish whether $(G,*)$ is an abelian group or is $ε$-far from any abelian group over $G$. Using a novel approach, we present a tester in the PS-model (and consequently in the FS-model) that runs in time $\tilde O(\sqrt{|G|}+1/ε)$, improving upon the Goldreich-Tauber tester, which runs in time $O(|G|/ε)$. Additionally, our tester improves another tester by Goldreich and Tauber that runs in time $O(|G|^2)$ and makes $\tilde O(|G|+1/ε)$ queries. We further extend our result to testing subclasses of abelian groups ${\cal G}$ that are closed under isomorphism. Specifically, if one can decide in time $T$ whether an abelian group of the form $Z_{m_1}\times \cdots\times Z_{m_r}$ belongs to ${\cal G}$, then there exists a tester for ${\cal G}$ that runs in time $T+\tilde O(\sqrt{|G|}+1/ε)$ and makes $O(\sqrt{|G|}+1/ε)$ queries. This result gives testers that run in time $O(\sqrt{|G|}+1/ε)$ for subclasses such as abelian groups of rank at most $k$, abelian $p$-groups, and vector spaces over~$Z_p$.