Efficient Isomorphism Testing for a Class of Group Extensions

Author Francois Le Gall

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Francois Le Gall

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Francois Le Gall. Efficient Isomorphism Testing for a Class of Group Extensions. In 26th International Symposium on Theoretical Aspects of Computer Science. Leibniz International Proceedings in Informatics (LIPIcs), Volume 3, pp. 625-636, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2009)


The group isomorphism problem asks whether two given groups are isomorphic or not. Whereas the case where both groups are abelian is well understood and can be solved efficiently, very little is known about the complexity of isomorphism testing for nonabelian groups. In this paper we study this problem for a class of groups corresponding to one of the simplest ways of constructing nonabelian groups from abelian groups: the groups that are extensions of an abelian group $A$ by a cyclic group $\mathbb{Z}_m$. We present an efficient algorithm solving the group isomorphism problem for all the groups of this class such that the order of $A$ is coprime with $m$. More precisely, our algorithm runs in time almost linear in the orders of the input groups and works in the general setting where the groups are given as black-boxes.
  • Polynomial-time algorithms
  • Group isomorphism
  • Black-box groups


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