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We consider the isomorphism problem for groups specified by their multiplication tables. Until recently, the best published bound for the worst-case was achieved by the n^(log_p n + O(1)) generator-enumeration algorithm. In previous work…

Data Structures and Algorithms · Computer Science 2014-12-02 David J. Rosenbaum

Given two graphs $H$ and $G$, the Subgraph Isomorphism problem asks if $H$ is isomorphic to a subgraph of $G$. While NP-hard in general, algorithms exist for various parameterized versions of the problem: for example, the problem can be…

Data Structures and Algorithms · Computer Science 2013-08-27 Dániel Marx , Michał Pilipczuk

The $k$-dimensional Weisfeiler-Leman algorithm ($k$-WL) is a fruitful approach to the Graph Isomorphism problem. 2-WL corresponds to the original algorithm suggested by Weisfeiler and Leman over 50 years ago. 1-WL is the classical color…

Discrete Mathematics · Computer Science 2019-04-10 V. Arvind , Frank Fuhlbrück , Johannes Köbler , Oleg Verbitsky

The combinatorial refinement techniques have proven to be an efficient approach to isomorphism testing for particular classes of graphs. If the number of refinement rounds is small, this puts the corresponding isomorphism problem in a…

Combinatorics · Mathematics 2024-09-17 Laurence Kluge

Twin-width is a graph parameter introduced in the context of first-order model checking, and has since become a central parameter in algorithmic graph theory. While many algorithmic problems become easier on arbitrary classes of bounded…

Combinatorics · Mathematics 2026-01-12 Irene Heinrich , Moritz Lichter , Klara Pakhomenko , Simon Raßmann

We give a fixed-parameter tractable algorithm that, given a parameter $k$ and two graphs $G_1,G_2$, either concludes that one of these graphs has treewidth at least $k$, or determines whether $G_1$ and $G_2$ are isomorphic. The running time…

Data Structures and Algorithms · Computer Science 2014-12-11 Daniel Lokshtanov , Marcin Pilipczuk , Michał Pilipczuk , Saket Saurabh

We give an overview of recent advances on the graph isomorphism problem. Our main focus will be on Babai's quasi-polynomial time isomorphism test and subsequent developments that led to the design of isomorphism algorithms with a…

Data Structures and Algorithms · Computer Science 2021-01-15 Martin Grohe , Daniel Neuen

In this paper, we show that the constant-dimensional Weisfeiler-Leman algorithm for groups (Brachter & Schweitzer, LICS 2020) can be fruitfully used to improve parallel complexity upper bounds on isomorphism testing for several families of…

Data Structures and Algorithms · Computer Science 2025-09-09 Joshua A. Grochow , Michael Levet

The $k$-dimensional Weisfeiler-Leman algorithm is a powerful tool in graph isomorphism testing. For an input graph $G$, the algorithm determines a canonical coloring of $s$-tuples of vertices of $G$ for each $s$ between 1 and $k$. We say…

Computational Complexity · Computer Science 2020-05-20 Frank Fuhlbrück , Johannes Köbler , Oleg Verbitsky

In this paper, we investigate the computational complexity of isomorphism testing for finite groups and quasigroups, given by their multiplication tables. We crucially take advantage of their various decompositions to show the following: -…

Data Structures and Algorithms · Computer Science 2026-02-05 Dan Johnson , Michael Levet , Petr Vojtěchovský , Brett Widholm

In this paper we combine many of the standard and more recent algebraic techniques for testing isomorphism of finite groups (GpI) with combinatorial techniques that have typically been applied to Graph Isomorphism. In particular, we show…

Computational Complexity · Computer Science 2019-05-08 Peter A. Brooksbank , Joshua A. Grochow , Yinan Li , Youming Qiao , James B. Wilson

The Weisfeiler-Leman procedure is a widely-used technique for graph isomorphism testing that works by iteratively computing an isomorphism-invariant coloring of vertex tuples. Meanwhile, a fundamental tool in structural graph theory, which…

Discrete Mathematics · Computer Science 2022-07-19 Sandra Kiefer , Daniel Neuen

Graph isomorphism, a classical algorithmic problem, determines whether two input graphs are structurally identical or not. Interestingly, it is one of the few problems that is not yet known to belong to either the P or NP-complete…

Data Structures and Algorithms · Computer Science 2024-10-01 Sourav Dutta , Arnab Bhattacharya

Given a graph $F$, let $I(F)$ be the class of graphs containing $F$ as an induced subgraph. Let $W[F]$ denote the minimum $k$ such that $I(F)$ is definable in $k$-variable first-order logic. The recognition problem of $I(F)$, known as…

Computational Complexity · Computer Science 2023-06-22 Oleg Verbitsky , Maksim Zhukovskii

Lubiw showed that several variants of Graph Isomorphism are NP-complete, where the solutions are required to satisfy certain additional constraints [SICOMP 10, 1981]. One of these, called Isomorphism With Restrictions, is to decide for two…

Computational Complexity · Computer Science 2017-09-29 V. Arvind , Johannes Köbler , Sebastian Kuhnert , Jacobo Toran

In recent work, Rosenbaum and Wagner showed that isomorphism of explicitly listed $p$-groups of order $n$ could be tested in $n^{\frac{1}{2}\log_p n + O(p)}$ time, roughly a square root of the classical bound. The $O(p)$ term is entirely…

Computational Complexity · Computer Science 2015-11-03 Eugene M. Luks

The $k$-dimensional Weisfeiler-Leman ($k$-WL) algorithm is a simple combinatorial algorithm that was originally designed as a graph isomorphism heuristic. It naturally finds applications in Babai's quasipolynomial time isomorphism…

Discrete Mathematics · Computer Science 2026-01-13 Martin Grohe , Moritz Lichter , Daniel Neuen , Pascal Schweitzer

Two graphs $G$ and $H$ are homomorphism indistinguishable over a family of graphs $\mathcal{F}$ if for all graphs $F \in \mathcal{F}$ the number of homomorphisms from $F$ to $G$ is equal to the number of homomorphism from $F$ to $H$. Many…

Logic in Computer Science · Computer Science 2024-02-15 Tim Seppelt

The Graph Isomorphism problem has both theoretical and practical interest. In this paper we present an algorithm, called conauto-1.2, that efficiently tests whether two graphs are isomorphic, and finds an isomorphism if they are. This…

Data Structures and Algorithms · Computer Science 2011-06-23 Jose Luis Lopez-Presa , Antonio Fernandez Anta

The problem of Subgraph Isomorphism is defined as follows: Given a pattern H and a host graph G on n vertices, does G contain a subgraph that is isomorphic to H? Eppstein [SODA 95, J'GAA 99] gives the first linear time algorithm for…

Data Structures and Algorithms · Computer Science 2009-09-28 Frederic Dorn