2017/05/10 by Daniel Neuen, Neuen, Daniel, Pascal Schweitzer +1 · 9 citations
Computer Science · Mathematics · #Advanced Graph Theory Research #Combinatorics #Combinatorics (math.CO) #Complexity and Algorithms in Graphs #Computer science #Data Structures and Algorithms (cs.DS) #Discrete mathematics #FOS: Computer and information sciences #FOS: Mathematics #Graph #Graph homomorphism #Graph isomorphism #Interconnection Networks and Systems #Isomorphism (crystallography) #Line graph #Mathematics #Theoretical computer science #Voltage graph #cs.DS #math.CO
paper · pdf · doi:10.48550/arxiv.1705.03686
published in RWTH Publications (RWTH Aachen) (RWTH Aachen University) · 32 pages
arxiv created 2017/05/10 · openalex publication_date 2017/05/10 · arxiv updated 2017/05/11 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The state-of-the-art solvers for the graph isomorphism problem can readily solve generic instances with tens of thousands of vertices. Indeed, experiments show that on inputs without particular combinatorial structure the algorithms scale almost linearly. In fact, it is non-trivial to create challenging instances for such solvers and the number of difficult benchmark graphs available is quite limited. We describe a construction to efficiently generate small instances for the graph isomorphism problem that are difficult or even infeasible for said solvers. Up to this point the only other available instances posing challenges for isomorphism solvers were certain incidence structures of combinatorial objects (such as projective planes, Hadamard matrices, Latin squares, etc.). Experiments show that starting from 1500 vertices our new instances are several orders of magnitude more difficult on comparable input sizes. More importantly, our method is generic and efficient in the sense that one can quickly create many isomorphism instances on a desired number of vertices. In contrast to this, said combinatorial objects are rare and difficult to generate and with the new construction it is possible to generate an abundance of instances of arbitrary size. Our construction hinges on the multipedes of Gurevich and Shelah and the Cai-Fürer-Immerman gadgets that realize a certain abelian automorphism group and have repeatedly played a role in the context of graph isomorphism. Exploring limits of such constructions, we also explain that there are group theoretic obstructions to generalizing the construction with non-abelian gadgets.