Hypergraph Isomorphism for Groups with Restricted Composition Factors

Abstract

We consider the isomorphism problem for hypergraphs taking as input two hypergraphs over the same set of vertices V and a permutation group Γ over domain V, and asking whether there is a permutation γ ε Γ that proves the two hypergraphs to be isomorphic. We show that for input groups, all of whose composition factors are isomorphic to a subgroup of the symmetric group on d points, this problem can be solved in time (n + m)O((log d)c) for some absolute constant c where n denotes the number of vertices and m the number of hyperedges. In particular, this gives the currently fastest isomorphism test for hypergraphs in general. The previous best algorithm for this problem due to Schweitzer and Wiebking (STOC 2019) runs in time nO(d)mO(1). As an application of this result, we obtain, for example, an algorithm testing isomorphism of graphs excluding K3,h (h ≥ 3) as a minor in time nO((log h)c). In particular, this gives an isomorphism test for graphs of Euler genus at most g running in time nO((log g)c).