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A cograph is a simple graph which contains no path on 4 vertices as an induced subgraph. We consider the eigenvalues of adjacency matrices of cographs and prove that a graph $G$ is a cograph if and only if no induced subgraph of $G$ has an…

Combinatorics · Mathematics 2018-10-01 Ebrahim Ghorbani

Digraphs are generalizations of graphs in which each edge is assigned with a direction or two directions. In this paper, we define discrete Morse functions on digraphs, and prove that the homology of the Morse complex and the path homology…

Algebraic Topology · Mathematics 2020-07-28 Chong Wang , Shiquan Ren

This paper presents several algorithms for hashing directed graphs. The algorithms given are capable of hashing entire graphs as well as assigning hash values to specific nodes in a given graph. The notion of node symmetry is made precise…

Discrete Mathematics · Computer Science 2023-06-21 Caleb Helbling

Let D be a simple digraph without loops or digons. For any v in V(D) let N_1(v) be the set of all nodes at out-distance 1 from v and let N_2(v) be the set of all nodes at out-distance 2. We provide sufficient conditions under which there…

Combinatorics · Mathematics 2008-08-19 James N. Brantner , Greg Brockman , Bill Kay , Emma E. Snively

When all non-edge distances of a graph realized in $\mathbb{R}^{d}$ as a {\em bar-and-joint framework} are generically {\em implied} by the bar (edge) lengths, the graph is said to be {\em rigid} in $\mathbb{R}^{d}$. For $d=3$,…

Computational Geometry · Computer Science 2013-11-20 Jialong Cheng , Meera Sitharam , Ileana Streinu

A k-regular graph on v vertices is a divisible design graph with parameters (v, k, lambda_1 ,lambda_2, m, n) if its vertex set can be partitioned into m classes of size n, such that any two different vertices from the same class have…

Combinatorics · Mathematics 2021-12-01 Vladislav V. Kabanov

Knowledge Graphs (KG) constitute a flexible representation of complex relationships between entities particularly useful for biomedical data. These KG, however, are very sparse with many missing edges (facts) and the visualisation of the…

Artificial Intelligence · Computer Science 2016-12-08 Armando Vieira

Graph Self-Supervised Learning (GSSL) offers a powerful paradigm for learning graph representations without labeled data. However, existing work assumes clean, manually curated graphs. Recent advances in NLP enable the large-scale automatic…

Machine Learning · Computer Science 2026-05-08 Othmane Kabal , Mounira Harzallah , Fabrice Guillet , Hideaki Takeda , Ryutaro Ichise

In this paper we introduce the graph $\Gamma_{sc}(G)$ associated with a group $G$, called the solvable conjugacy class graph (abbreviated as SCC-graph), whose vertices are the nontrivial conjugacy classes of $G$ and two distinct conjugacy…

Combinatorics · Mathematics 2022-02-08 Parthajit Bhowal , Peter J. Cameron , Rajat Kanti Nath , Benjamin Sambale

A vertex with neighbours of degrees $d_1 \geq ... \geq d_r$ has {\em vertex type} $(d_1, ..., d_r)$. A graph is {\em vertex-oblique} if each vertex has a distinct vertex-type. While no graph can have distinct degrees, Schreyer, Walther and…

Combinatorics · Mathematics 2007-05-23 Alastair Farrugia

A graph $G$ is $\textit{universal}$ for a (finite) family $\mathcal{H}$ of graphs if every $H \in \mathcal{H}$ is a subgraph of $G$. For a given family $\mathcal{H}$, the goal is to determine the smallest number of edges an…

Combinatorics · Mathematics 2024-01-12 Noga Alon , Natalie Dodson , Carmen Jackson , Rose McCarty , Rajko Nenadov , Lani Southern

Edges in real-world graphs are typically formed by a variety of factors and carry diverse relation semantics. For example, connections in a social network could indicate friendship, being colleagues, or living in the same neighborhood.…

Social and Information Networks · Computer Science 2022-02-24 Tianxiang Zhao , Xiang Zhang , Suhang Wang

Singular Value Decomposition (SVD) is a powerful tool in linear algebra.We propose an extension of SVD for both the qualitative detection and quantitative determination of nonlinearity in a time series. The paper illustrates nonlinear SVD…

Chaotic Dynamics · Physics 2009-02-11 Prabhakar G. Vaidya , Sajini Anand P. S , Nithin Nagaraj

In order to define the process of restrosynthesis of a new organic molecule, it is often necessary to be able to draw inspiration from that of a molecule similar to the target one of which we know such a process. To compute such a…

Data Structures and Algorithms · Computer Science 2018-07-13 Stéfi Nouleho , Dominique Barth , Franck Quessette , Marc-Antoine Weisser , Dimitri Watel , Olivier David

Several researchers have recently explored various graph parameters that can or cannot be characterized by the spectrum of a matrix associated with a graph. In this paper we show that several NP-hard zero forcing numbers are not…

Combinatorics · Mathematics 2022-04-25 Aida Abiad , Boris Brimkov , Jane Breen , Thomas R. Cameron , Himanshu Gupta , Ralihe R. Villagrán

Assume that $G$ is a finite group. For every $a, b \in\mathbb N,$ we define a graph $\Gamma_{a,b}(G)$ whose vertices correspond to the elements of $G^a\cup G^b$ and in which two tuples $(x_1,\dots,x_a)$ and $(y_1,\dots,y_b)$ are adjacent if…

Group Theory · Mathematics 2020-06-23 Cristina Acciarri , Andrea Lucchini

A total dominating set in a graph is a set of vertices such that every vertex of the graph has a neighbor in the set. We introduce and study graphs that admit non-negative real weights associated to their vertices such that a set of…

Combinatorics · Mathematics 2015-05-12 Nina Chiarelli , Martin Milanic

A circulant graph is a simple graph whose adjacency matrix can be represented in the form of a circulant matrix, while a nut graph is considered to be a graph whose null space is spanned by a single full vector. In a previous study by…

Combinatorics · Mathematics 2026-01-26 Ivan Damnjanović

We give inductive constructions of independent graphs that contain implied nonedges but do not contain any non-trivial rigid subgraphs, or \emph{nucleations}: some of the constructions and proofs apply to 3-dimensional abstract rigidity…

Combinatorics · Mathematics 2025-08-19 Jialong Cheng , Meera Sitharam , Ileana Streinu , William Sims

Very sparse random graphs are known to typically be singular (i.e., have singular adjacency matrix), due to the presence of "low-degree dependencies'' such as isolated vertices and pairs of degree-1 vertices with the same neighbourhood. We…

Probability · Mathematics 2024-03-27 Asaf Ferber , Matthew Kwan , Ashwin Sah , Mehtaab Sawhney