Automorphically Equivalent Elements of Finite Abelian Groups
Agarwal, Arjun, R.C. Chen, Garg, Rohan, Jared Kettinger · arXiv (Cornell University) · 2025
Given a finite abelian group $G$ and elements $x, y \in G$, we prove that there exists $ϕ\in \text{Aut}(G)$ such that $ϕ(x) = y$ if and only if $G/\langle x \rangle \cong G/\langle y \rangle$. This result leads to our development of the two fastest known algorithms to determine if two elements of a finite abelian group are automorphic images of one another. The second algorithm also computes $G/\langle x \rangle$ in a near-linear time algorithm for groups, most feasible when the group has exponent at most $10^{20}$. We conculde with an algorithm that computes the automorphic orbits of finite abelian groups.