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Let X be a 2-dimensional simplicial complex. The degree of an edge e is the number of 2-faces of X containing e. The complex X is an \epsilon-expander if the coboundary d_1(\phi) of every Z_2-valued 1-cochain \phi \in C^1(X;Z_2) satisfies…

组合数学 · 数学 2013-07-16 Alexander Lubotzky , Roy Meshulam

A set of vertices $W$ resolves a graph $G$ if every vertex is uniquely determined by its vector of distances to the vertices in $W$. A metric dimension of $G$ is the minimum cardinality of a resolving set of $G$. A bipartite graph G(n,n) is…

组合数学 · 数学 2015-03-17 S. W. Saputro , E. T. Baskoro , A. N. M. Salman , D. Suprijanto , And M. Baca

An edge-coloring of a graph $G$ with colors $1,...,t$ is called an interval $t$-coloring if all colors are used, and the colors of edges incident to any vertex of $G$ are distinct and form an interval of integers. In 1991 Erd\H{o}s…

组合数学 · 数学 2013-01-21 Petros A. Petrosyan , Hrant H. Khachatrian

A connected graph, on four or more vertices, is matching covered (aka 1-extendable) if every edge is present in some perfect matching. An ear decomposition theorem exists for bipartite matching covered graphs due to Hetyei. From the results…

组合数学 · 数学 2026-05-21 Amit Kumar Mallik , Ajit A. Diwan , Nishad Kothari

The set A of distinct scores of the vertices of an oriented bipartite graph D(U, V) is called its score set. We consider the following question: given a finite, nonempty set A of positive integers, is there an oriented bipartite graph D(U,…

组合数学 · 数学 2007-05-23 S. Pirzada , T. A. Naikoo , T. A. Chishti

Let G be a family of n-vertex graphs of uniform degree 2 with the property that the union of any two member graphs has degree four. We determine the leading term in the asymptotics of the largest cardinality of such a family. Several…

组合数学 · 数学 2012-08-10 János Körner , Irene Muzi

The first multiplicative Zagreb index of a graph $G$ is the product of the square of every vertex degree, while the second multiplicative Zagreb index is the product of the degree of each edge over all edges. In our work, we explore the…

组合数学 · 数学 2017-04-28 Chunxiang Wang , Jia-Bao Liu , Shaohui Wang

Given a bipartite graph with bipartition $(A,B)$ where $B$ is equipartitioned into $k\ge2$ blocks, can the vertices in $A$ be picked one by one so that at every step, the picked vertices cover roughly the same number of vertices in each of…

组合数学 · 数学 2021-07-13 Tung H. Nguyen

An edge $e$ of a matching covered graph $G$ is removable if $G-e$ is also matching covered. The notion of removable edge arises in connection with ear decompositions of matching covered graphs introduced by Lov\'asz and Plummer. A…

组合数学 · 数学 2024-06-04 Yipei Zhang , Fuliang Lu , Xiumei Wang , Jinjiang Yuan

A half-square of a bipartite graph $B=(X,Y,E_B)$ has one color class of $B$ as vertex set, say $X$; two vertices are adjacent whenever they have a common neighbor in $Y$. If $G=(V,E_G)$ is the half-square of a planar bipartite graph…

离散数学 · 计算机科学 2018-12-12 Hoang-Oanh Le , Van Bang Le

In a recent work on the bipartite Erd\H{o}s-R\'{e}nyi graph, Do et al. (2023) established upper bounds on the number of connected labeled bipartite graphs with a fixed surplus. We use some recent encodings of bipartite random graphs in…

组合数学 · 数学 2024-11-15 David Clancy

Biregular bipartite graphs have been proven to have similar edge distributions to random bipartite graphs and thus have nice pseudorandomness and expansion properties. Thus it is quite desirable to find a biregular bipartite spanning…

组合数学 · 数学 2024-10-29 Dandan Fan , Xiaofeng Gu , Huiqiu Lin

For a graph $G=(V,E)$, let $bc(G)$ denote the minimum number of pairwise edge disjoint complete bipartite subgraphs of $G$ so that each edge of $G$ belongs to exactly one of them. It is easy to see that for every graph $G$, $bc(G) \leq n…

组合数学 · 数学 2014-09-23 Noga Alon , Tom Bohman , Hao Huang

In this paper, we explore the design and analysis of regular bipartite graphs motivated by their application in low-density parity-check (LDPC) codes specifically with constrained girth and in the high-rate regime. We focus on the relation…

信息论 · 计算机科学 2025-06-16 Sheida Rabeti , Mohsen Moradi , Hessam Mahdavifar

A graph $G$ with vertex set $V(G)$ and edge set $E(G)$ is said to be word-representable if there exists a word $w$ over the alphabet $V(G)$ such that, for any two distinct letters $x,y \in V(G)$, the letters $x$ and $y$ alternate in $w$ if…

组合数学 · 数学 2026-04-14 Eshwar Srinivasan , Ramesh Hariharasubramanian

In this paper we introduce a generalization of the well known concept of a graceful labeling. Given a graph G with e=dm edges, we call d-graceful labeling of G an injective function from V(G) to the set {0,1,2,..., d(m+1)-1} such that…

组合数学 · 数学 2012-09-10 A. Pasotti

A strong edge-coloring of a graph $G$ is an assignment of colors to edges such that every color class induces a matching. We here focus on bipartite graphs whose one part is of maximum degree at most $3$ and the other part is of maximum…

离散数学 · 计算机科学 2015-08-19 Julien Bensmail , Aurélie Lagoutte , Petru Valicov

The Erd\H{o}s-S\'{o}s Conjecture states that every graph with average degree more than $k-2$ contains all trees of order $k$ as subgraphs. In this paper, we consider a variation of the above conjecture: studying the maximum size of an…

组合数学 · 数学 2017-02-13 Long-Tu Yuan , Xiao-Dong Zhang

An acyclic digraph in which every vertex has indegree at most $i$ and outdegree at most $j$ is called an $(i,j)$ digraph for some positive integers $i$ and $j$. The phylogeny graph of a digraph $D$ has $V(D)$ as the vertex set and an edge…

组合数学 · 数学 2024-10-08 Myungho Choi , Suh-Ryung Kim

Let G=(V,E) be a graph. A set S is independent if no two vertices from S are adjacent, alpha(G) is the size of a maximum independent set, and core(G) is the intersection of all maximum independent sets. The number d(X)=|X|-|N(X)| is the…

离散数学 · 计算机科学 2011-02-10 Vadim E. Levit , Eugen Mandrescu