3-对数空间中连通平面图同构

Restricted Space Algorithms for Isomorphism on Bounded Treewidth Graphs

The Graph Isomorphism problem restricted to graphs of bounded treewidth or bounded tree distance width are known to be solvable in polynomial time [Bod90],[YBFT99]. We give restricted space algorithms for these problems proving the following results: - Isomorphism for bounded tree distance width graphs is in L and thus complete for the class. We also show that for this kind of graphs a canon can be computed within logspace. - For bounded treewidth graphs, when both input graphs are given together with a tree decomposition, the problem of whether there is an isomorphism which respects the decom…

Faster FPT Algorithm for Graph Isomorphism Parameterized by Eigenvalue Multiplicity

We give a $O^*(k^{O(k)})$ time isomorphism testing algorithm for graphs of eigenvalue multiplicity bounded by $k$ which improves on the previous best running time bound of $O^*(2^{O(k^2/\log k)})$.

用博弈法并行测试图同构

Testing Graph Isomorphism in Parallel by Playing a Game

我们的出发点是观察到，如果在一个类C中的图具有低描述的复杂性在一阶逻辑，那么同构问题C是可解决的快速并行算法（本质上，由一个简单的组合算法称为多维Weisfeiler-Lehman算法）。使用这种方法，我们证明了有界树宽的图的同构是可测试的TC 1，回答了一个开放的问题所提出的Escherasekharan。此外，我们得到了一个AC 1算法测试同构的旋转系统（组合规格的图嵌入）。AC 1上界以前是已知的，但这个界可以通过简单的Weisfeiler-Lehman算法实现的事实是新的。结合已有的结果，给出了平面图的一个新的AC 1同构算法。

逐项对数矩阵代数与平面图同态的二分类（第一部分）

Entrywise Logarithmic Matrix Algebra and Dichotomy of Planar Graph Homomorphisms

本文通过逐项对数矩阵代数与平面边小工具，对非负权重平面图同态计数问题给出三分复杂度分类，核心证明正定矩阵情形，并区分FKT可解与#P-困难情形。

Canonizing Graphs of Bounded Tree Width in Logspace

Graph canonization is the problem of computing a unique representative, a canon, from the isomorphism class of a given graph. This implies that two graphs are isomorphic exactly if their canons are equal. We show that graphs of bounded tree width can be canonized by logarithmic-space (logspace) algorithms. This implies that the isomorphism problem for graphs of bounded tree width can be decided in logspace. In the light of isomorphism for trees being hard for the complexity class logspace, this makes the ubiquitous class of graphs of bounded tree width one of the few classes of graphs for whic…

基于代码等价的群同构并行算法

Parallel Algorithms for Group Isomorphism via Code Equivalence

本文基于代码等价，提出了一种在AC³复杂度内测试群同构的算法，改进了群同构测试的复杂度界限。

Group isomorphism is nearly-linear time for most orders

We show that there is a dense set $\ourset\subseteq \mathbb{N}$ of group orders and a constant $c$ such that for every $n\in \ourset$ we can decide in time $O(n^2(\log n)^c)$ whether two $n\times n$ multiplication tables describe isomorphic groups of order $n$. This improves significantly over the general $n^{O(\log n)}$-time complexity and shows that group isomorphism can be tested efficiently for almost all group orders $n$. We also show that in time $O(n^2 (\log n)^c)$ it can be decided whether an $n\times n$ multiplication table describes a group; this improves over the known $O(n^3)$ comp…

Bidirectional Collision Detection and Faster Deterministic Isomorphism Testing

In this work, we introduce bidirectional collision detection --- a new algorithmic tool that applies to the collision problems that arise in many isomorphism problems. For the group isomorphism problem, we show that bidirectional collision detection yields a deterministic n^((1 / 2) log n + O(1)) time algorithm whereas previously the n^(log n + O(1)) generator-enumeration algorithm was the best result for several decades. For the hard special case of solvable groups, we combine bidirectional collision detection with methods from the author's previous work to obtain a deterministic square-root …

On the Group and Color Isomorphism Problems

In this paper, we prove results on the relationship between the complexity of the group and color isomorphism problems. The difficulty of color isomorphism problems is known to be closely linked to the the composition factors of the permutation group involved. Previous works are primarily concerned with applying color isomorphism to bou nded degree graph isomorphism, and have therefore focused on the alternating composit ion factors, since those are the bottleneck in the case of graph isomorphism. We consider the color isomorphism problem with composition factors restricted to those other than…

Planarity Testing Revisited

Planarity Testing is the problem of determining whether a given graph is planar while planar embedding is the corresponding construction problem. The bounded space complexity of these problems has been determined to be exactly Logspace by Allender and Mahajan with the aid of Reingold's result. Unfortunately, the algorithm is quite daunting and generalizing it to say, the bounded genus case seems a tall order. In this work, we present a simple planar embedding algorithm running in logspace. We hope this algorithm will be more amenable to generalization. The algorithm is based on the fact that 3…

Approximations of Isomorphism and Logics with Linear-Algebraic Operators

Invertible map equivalences are approximations of graph isomorphism that refine the well-known Weisfeiler-Leman method. They are parametrised by a number k and a set Q of primes. The intuition is that two graphs G and H which are equivalent with respect to k-Q-IM-equivalence cannot be distinguished by a refinement of k-tuples given by linear operators acting on vector spaces over fields of characteristic p, for any p in Q. These equivalences first appeared in the study of rank logic, but in fact they can be used to delimit the expressive power of any extension of fixed-point logic with linear-…

Fixed-parameter tractable canonization and isomorphism test for graphs of bounded treewidth

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 of the algorithm on an $n$-vertex graph is $2^{O(k^5\log k)}\cdot n^5$, and this is the first fixed-parameter algorithm for Graph Isomorphism parameterized by treewidth. Our algorithm in fact solves the more general canonization problem. We namely design a procedure working in $2^{O(k^5\log k)}\cdot n^5$ time that, for a given graph $G$ on $n$ vertices, eit…

Graph isomorphism in quasipolynomial time parameterized by treewidth

We extend Babai's quasipolynomial-time graph isomorphism test (STOC 2016) and develop a quasipolynomial-time algorithm for the multiple-coset isomorphism problem. The algorithm for the multiple-coset isomorphism problem allows to exploit graph decompositions of the given input graphs within Babai's group-theoretic framework. We use it to develop a graph isomorphism test that runs in time $n^{\operatorname{polylog}(k)}$ where $n$ is the number of vertices and $k$ is the minimum treewidth of the given graphs and $\operatorname{polylog}(k)$ is some polynomial in $\operatorname{log}(k)$. Our resul…

关于图同构的量子筛算法的不可能性

On the Impossibility of a Quantum Sieve Algorithm for Graph Isomorphism

众所周知，在隐藏子群问题（HSP）的框架内工作的图同构的任何量子算法必须在Omega（n log n）陪集状态上执行高度纠缠的测量。如何有效地进行这种测量的唯一已知模型之一是用于二面体群中HSP的Kuperberg算法，其中量子态根据张量积分解为不可约表示而自适应地组合和测量。这种“量子筛”从陪集态开始，一路向下，直到概率不同的表示，例如，隐藏的子群是平凡的还是非平凡的。在本文中，我们给出了强有力的证据，没有这样的方法可以成功的图同构。特别地，我们考虑图同构到圈积S_n \wr Z_2上的HSP的自然约化。我们证明，模的对称群的渐近性质的群论猜想，无论我们使用什么规则来自适应组合量子态，有一个常数b > 0，使得在这个家庭中没有算法可以解决图同构在e^{b sqrt{n}}时间。特别地，这样的算法本质上不比最好的已知经典算法好，其运行时间是e^{O（sqrt{n \log n}）}。

On the Isomorphism Problem for Helly Circular-Arc Graphs

The isomorphism problem is known to be efficiently solvable for interval graphs, while for the larger class of circular-arc graphs its complexity status stays open. We consider the intermediate class of intersection graphs for families of circular arcs that satisfy the Helly property. We solve the isomorphism problem for this class in logarithmic space. If an input graph has a Helly circular-arc model, our algorithm constructs it canonically, which means that the models constructed for isomorphic graphs are equal.

Logarithmic Weisfeiler-Leman Identifies All Planar Graphs

The Weisfeiler-Leman (WL) algorithm is a well-known combinatorial procedure for detecting symmetries in graphs and it is widely used in graph-isomorphism tests. It proceeds by iteratively refining a colouring of vertex tuples. The number of iterations needed to obtain the final output is crucial for the parallelisability of the algorithm. We show that there is a constant k such that every planar graph can be identified (that is, distinguished from every non-isomorphic graph) by the k-dimensional WL algorithm within a logarithmic number of iterations. This generalises a result due to Verbitsky …

Algorithms for group isomorphism via group extensions and cohomology

The isomorphism problem for finite groups of order n (GpI) has long been known to be solvable in $n^{\log n+O(1)}$ time, but only recently were polynomial-time algorithms designed for several interesting group classes. Inspired by recent progress, we revisit the strategy for GpI via the extension theory of groups. The extension theory describes how a normal subgroup N is related to G/N via G, and this naturally leads to a divide-and-conquer strategy that splits GpI into two subproblems: one regarding group actions on other groups, and one regarding group cohomology. When the normal subgroup N …

Graph Isomorphism in Quasipolynomial Time

We show that the Graph Isomorphism (GI) problem and the related problems of String Isomorphism (under group action) (SI) and Coset Intersection (CI) can be solved in quasipolynomial ($\exp((\log n)^{O(1)})$) time. The best previous bound for GI was $\exp(O(\sqrt{n\log n}))$, where $n$ is the number of vertices (Luks, 1983); for the other two problems, the bound was similar, $\exp(\tilde{O}(\sqrt{n}))$, where $n$ is the size of the permutation domain (Babai, 1983). The algorithm builds on Luks's SI framework and attacks the barrier configurations for Luks's algorithm by group theoretic "local c…