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A \emph{mixed interval graph} is an interval graph that has, for every pair of intersecting intervals, either an arc (directed arbitrarily) or an (undirected) edge. We are particularly interested in scenarios where edges and arcs are…

Discrete Mathematics · Computer Science 2024-08-09 Grzegorz Gutowski , Konstanty Junosza-Szaniawski , Felix Klesen , Paweł Rzążewski , Alexander Wolff , Johannes Zink

The graphical notion of effective resistance has found wide-ranging applications in many areas of pure mathematics, applied mathematics and control theory. By the nature of its construction, effective resistance can only be computed in…

Optimization and Control · Mathematics 2013-10-23 George Forrest Young , Luca Scardovi , Naomi Ehrich Leonard

A mixed graph $G$ is a graph obtained from a simple undirected graph by orientating a subset of edges. $G$ is self-converse if it is isomorphic to the graph obtained from $G$ by reversing each directed edge. For two mixed graphs $G$ and $H$…

Combinatorics · Mathematics 2019-12-02 Wei Wang , Lihong Qiu , Jianguo Qian , Wei Wang

Given any graph $G$, the (adjacency) spread of $G$ is the maximum absolute difference between any two eigenvalues of the adjacency matrix of $G$. In this paper, we resolve a pair of 20-year-old conjectures of Gregory, Hershkowitz, and…

Combinatorics · Mathematics 2021-09-08 Jane Breen , Alex W. N. Riasanovsky , Michael Tait , John Urschel

It is now well known that ultracontractive properties of semigroups with infinitesimal generator given by an undirected graph Laplacian operator can be obtained through an understanding of the geometry of the underlying infinite weighted…

Dynamical Systems · Mathematics 2020-04-10 Jason J. Bramburger

A unified framework for the Expander Mixing Lemma for irregular graphs using adjacency eigenvalues is presented, as well as two new versions of it. While the existing Expander Mixing Lemmas for irregular graphs make use of the notion of…

Combinatorics · Mathematics 2024-07-17 Aida Abiad , Sjanne Zeijlemaker

In this paper, we initiate the study of the dynamic maintenance of $2$-edge-connectivity relationships in directed graphs. We present an algorithm that can update the $2$-edge-connected blocks of a directed graph with $n$ vertices through a…

Data Structures and Algorithms · Computer Science 2016-07-26 Loukas Georgiadis , Giuseppe F. Italiano , Nikos Parotsidis

Inspired by earlier results about proper and polychromatic coloring of hypergraphs, we investigate such colorings of directed hypergraphs, that is, hypergraphs in which the vertices of each hyperedge is partitioned into two parts, a tail…

Combinatorics · Mathematics 2022-05-24 Balázs Keszegh

Given a simple graph $G$, its Laplacian-energy-like invariant $LEL(G)$ and incidence energy $IE(G)$ are the sum of square root of its all Laplacian eigenvalues and signless Laplacian eigenvalues, respectively. Applying the Cauchy-Schwarz…

Combinatorics · Mathematics 2017-09-19 Gui-Xian Tian , Shu-Yu Cui

Graph sampling is the problem of choosing a node subset via sampling matrix $\mathbf{H} \in \{0,1\}^{K \times N}$ to collect samples $\mathbf{y} = \mathbf{H} \mathbf{x} \in \mathbb{R}^K$, $K < N$, so that the target signal $\mathbf{x} \in…

Signal Processing · Electrical Eng. & Systems 2022-10-27 Yuejiang Li , Hong Vicky Zhao , Gene Cheung

To deal with irregular data structure, graph convolution neural networks have been developed by a lot of data scientists. However, data scientists just have concentrated primarily on developing deep neural network method for un-directed…

Machine Learning · Statistics 2022-09-07 Loc Hoang Tran , Linh Hoang Tran

In a directed graph, the imbalance of a vertex is its outdegree minus its indegree. We characterize the sequences that are realizable as the sequence of imbalances of a simple directed graph. Moreover, a realization of a realizable sequence…

Combinatorics · Mathematics 2007-05-23 Dhruv Mubayi , Todd G. Will , Douglas B. West

Coboundary and cosystolic expansion are notions of expansion that generalize the Cheeger constant or edge expansion of a graph to higher dimensions. The classical Cheeger inequality implies that for graphs edge expansion is equivalent to…

Combinatorics · Mathematics 2021-02-11 Tali Kaufman , Izhar Oppenheim

In this paper we study the relationship of hyperbolicity and (Cheeger) isoperimetric inequality in the context of Riemannian manifolds and graphs. We characterize the hyperbolic manifolds and graphs (with bounded local geometry) verifying…

Metric Geometry · Mathematics 2016-05-17 Álvaro Martínez-Pérez , José M. Rodríguez

We introduce and investigate the approximability of the maximum binary tree problem (MBT) in directed and undirected graphs. The goal in MBT is to find a maximum-sized binary tree in a given graph. MBT is a natural variant of the…

Discrete Mathematics · Computer Science 2020-07-24 Karthekeyan Chandrasekaran , Elena Grigorescu , Gabriel Istrate , Shubhang Kulkarni , Young-San Lin , Minshen Zhu

We introduce a method to embed edge-colored graphs into families of expander graphs, which generalizes a framework developed by Dragani\'c, Krivelevich, and Nenadov (2022). As an application, we show that each family of sufficiently…

Combinatorics · Mathematics 2025-01-27 Ben Lund , Chuandong Xu

We give a polynomial-time algorithm for computing upper bounds on some of the smaller energy eigenvalues in a spin-1/2 ferromagnetic Heisenberg model with any graph $G$ for the underlying interactions. An important ingredient is the…

Quantum Physics · Physics 2019-07-29 Yingkai Ouyang

Let $D$ be an oriented graph with skew adjacency matrix $S(D)$. Two oriented graphs $D$ and $C$ are said to share the same generalized skew spectrum if $S(D)$ and $S(C)$ have the same eigenvalues, and $J-S(D)$ and $J-S(C)$ also have the…

Combinatorics · Mathematics 2025-04-25 Muhammad Raza , Obaid Ullah Ahmed , Mudassir Shabbir , Xenofon Koutsoukos , Waseem Abbas

Networks are one of the most valuable data structures for modeling problems in the real world. However, the most recent node embedding strategies have focused on undirected graphs, with limited attention to directed graphs, especially…

Machine Learning · Computer Science 2023-11-27 Xiyang Sun , Fumiyasu Komaki

For distinct vertices $u$ and $v$ in a graph $G$, the {\em connectivity} between $u$ and $v$, denoted $\kappa_G(u,v)$, is the maximum number of internally disjoint $u$--$v$ paths in $G$. The {\em average connectivity} of $G$, denoted…

Combinatorics · Mathematics 2019-07-18 Rocio M. Casablanca , Peter Dankelmann , Wayne Goddard , Ortrud R. Oellermann , Lucas Mol
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