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We describe an infinite family of graphs $G_n$, where $G_n$ has $n$ vertices, independence number at least $n/4$, and no set of less than $\sqrt{n}/2$ vertices intersects all its maximum independent sets. This is motivated by a question of…

Combinatorics · Mathematics 2021-04-06 Noga Alon

Distance-hereditary graphs form an important class of graphs, from the theoretical point of view, due to the fact that they are the totally decomposable graphs for the split-decomposition. The previous best enumerative result for these…

Combinatorics · Mathematics 2016-08-05 Cédric Chauve , Éric Fusy , Jérémie Lumbroso

A fair dominating set in a graph $G$ (or FD-set) is a dominating set $S$ such that all vertices not in $S$ are dominated by the same number of vertices from $S$; that is, every two vertices not in $S$ have the same number of neighbors in…

Combinatorics · Mathematics 2011-09-07 Yair Caro , Adriana Hansberg , Michael A. Henning

The edit distance between two graphs on the same vertex set is defined to be size of the symmetric difference of their edge sets. The edit distance function of a hereditary property, $\mathcal{H}$, is a function of $p$ and measures,…

Combinatorics · Mathematics 2011-02-22 Ryan Martin , Tracy McKay

We present exact and heuristic algorithms that find, for a given family of graphs, a graph that contains each member of the family as an induced subgraph. For $0 \leq k \leq 6$, we give the minimum number of vertices $f(k)$ in a graph…

Combinatorics · Mathematics 2021-10-26 James Trimble

We give a simple method to estimate the number of distinct copies of some classes of spanning subgraphs in hypergraphs with high minimum degree. In particular, for each $k\geq 2$ and $1\leq \ell\leq k-1$, we show that every $k$-graph on $n$…

Combinatorics · Mathematics 2024-11-20 Richard Montgomery , Matías Pavez-Signé

We define the limiting density of a minor-closed family of simple graphs F to be the smallest number k such that every n-vertex graph in F has at most kn(1+o(1)) edges, and we investigate the set of numbers that can be limiting densities.…

Combinatorics · Mathematics 2010-10-18 David Eppstein

Let $c(H)$ be the smallest value for which $e(G)/|G|\geq c(H)$ implies $H$ is a minor of $G$. We show a new upper bound on $c(H)$, which improves previous bounds for graphs with a vertex partition where some pairs of parts have many more…

Combinatorics · Mathematics 2021-10-18 Matthew Wales

We give an efficient randomized algorithm to construct a box representation of any graph G on n vertices in $1.5 (\Delta + 2) \ln n$ dimensions, where $\Delta$ is the maximum degree of G. We also show that $\boxi(G) \le (\Delta + 2) \ln n$…

Discrete Mathematics · Computer Science 2007-07-31 L. Sunil Chandran , Mathew C Francis , Naveen Sivadasan

In 2002, D. Fon-Der-Flaass constructed a prolific family of strongly regular graphs. In this paper, we prove that for infinitely many natural numbers $n$, this family contains $n^{\Omega(n^{2/3})}$ strongly regular $n$-vertex graphs $X$…

Combinatorics · Mathematics 2023-12-04 Jinzhuan Cai , Jin Guo , Alexander L. Gavrilyuk , Ilia Ponomarenko

Call a simple graph $H$ of order $n$ well-separable, if by deleting a separator set of size $o(n)$ the leftover will have components of size at most $o(n)$. We prove, that bounded degree well-separable spanning subgraphs are easy to embed:…

Combinatorics · Mathematics 2007-07-18 Béla Csaba

For unweighted graphs, finding isometric embeddings is closely related to decompositions of $G$ into Cartesian products of smaller graphs. When $G$ is isomorphic to a Cartesian graph product, we call the factors of this product a…

Data Structures and Algorithms · Computer Science 2021-12-15 Kristin Sheridan , Joseph Berleant , Mark Bathe , Anne Condon , Virginia Vassilevska Williams

Let $f(n)$ be the smallest number such that every collection of $n$ matchings, each of size at least $f(n)$, in a bipartite graph, has a full rainbow matching. Generalizing famous conjectures of Ryser, Brualdi and Stein, Aharoni and Berger…

Combinatorics · Mathematics 2017-02-24 Ron Aharoni , Dani Kotlar , Ran Ziv

A graph $G$ is contractible to a graph $H$ if there is a set $X \subseteq E(G)$, such that $G/X$ is isomorphic to $H$. Here, $G/X$ is the graph obtained from $G$ by contracting all the edges in $X$. For a family of graphs $\cal F$, the…

Data Structures and Algorithms · Computer Science 2025-05-21 Akanksha Agrawal , Fedor V. Fomin , Daniel Lokshtanov , Saket Saurabh , Prafullkumar Tale

We initiate the systematic study of the following Tur\'an-type question. Suppose $\Gamma$ is a graph with $n$ vertices such that the edge density between any pair of subsets of vertices of size at least $t$ is at most $1 - c$, for some $t$…

Combinatorics · Mathematics 2024-06-11 Jacob Fox , Rajko Nenadov , Huy Tuan Pham

In 1986 Lovasz, Spencer, and Vesztergombi proved a lower bound for the hereditary a discrepancy of a set system F in terms of determinants of square submatrices of the incidence matrix of F. As shown by an example of Hoffman, this bound can…

Combinatorics · Mathematics 2011-07-07 Jiri Matousek

The well-known Erd\H{o}s-Hajnal conjecture states that for any graph $F$, there exists $\epsilon>0$ such that every $n$-vertex graph $G$ that contains no induced copy of $F$ has a homogeneous set of size at least $n^{\epsilon}$. We consider…

Combinatorics · Mathematics 2023-03-20 Maria Axenovich , Dhruv Mubayi , Lea Weber

We investigate how small the Randi\'c index of a graph can be in terms of its matching number, and prove several results. We give best-possible linear bounds for graphs of small excess and for subcubic graphs; in the former case the size of…

Combinatorics · Mathematics 2024-08-21 Saieed Akbari , Sina Ghasemi Nezhad , Reyhane Ghazizadeh , John Haslegrave , Elahe Tohidi

In the companion paper [Linear rank-width of distance-hereditary graphs I. A polynomial-time algorithm, Algorithmica 78(1):342--377, 2017], we presented a characterization of the linear rank-width of distance-hereditary graphs, from which…

Combinatorics · Mathematics 2017-08-16 Mamadou Moustapha Kanté , O-joung Kwon

Every graph $G=(V,E)$ is an induced subgraph of some Kneser graph of rank $k$, i.e., there is an assignment of (distinct) $k$-sets $v \mapsto A_v$ to the vertices $v\in V$ such that $A_u$ and $A_v$ are disjoint if and only if $uv\in E$. The…

Combinatorics · Mathematics 2017-01-31 Zoltán Füredi , Ida Kantor
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