Browsing Combinatorics and Optimization by Type "Article"
Now showing items 21-40 of 52
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H-colouring Pt-free graphs in subexponential time
(Elsevier, 2019-08-31)A graph is called Pt-free if it does not contain the path on t vertices as an induced subgraph. Let H be a multigraph with the property that any two distinct vertices share at most one common neighbour. We show that the ... -
Induced Subgraphs and Tree Decompositions III. Three-Path-Configurations and Logarithmic Treewidth.
(Advances in Combinatorics, 2022-09-09)A theta is a graph consisting of two non-adjacent vertices and three internally disjoint paths between them, each of length at least two. For a family H of graphs, we say a graph G is H-free if no induced subgraph of G is ... -
Induced subgraphs of graphs with large chromatic number. VIII. Long odd holes
(Elsevier, 2020-01)We prove a conjecture of András Gyárfás, that for all k, l, every graph with clique number at most κ and sufficiently large chromatic number has an odd hole of length at least ℓ. -
List 3-Coloring Graphs with No Induced P6+rP3
(Springer Nature, 2021-01-01)For an integer t, we let Pt denote the t-vertex path. We write H+G for the disjoint union of two graphs H and G, and for an integer r and a graph H, we write rH for the disjoint union of r copies of H. We say that a graph ... -
List 3-coloring Pt-free graphs with no induced 1-subdivision of K1,s
(Elsevier, 2020-11)Let s and t be positive integers. We use Pt to denote the path with t vertices and K1,s to denote the complete bipartite graph with parts of size 1 and s respectively. The one-subdivision of K1,s is obtained by replacing ... -
Minimal induced subgraphs of two classes of 2-connected non-Hamiltonian graphs
(Elsevier, 2022-07)In 1981, Duffus, Gould, and Jacobson showed that every connected graph either has a Hamiltonian path, or contains a claw (K1,3) or a net (a fixed six-vertex graph) as an induced subgraph. This implies that subject to being ... -
Modular relations of the Tutte symmetric function
(Elsevier, 2022-04)For a graph G, its Tutte symmetric function XBG generalizes both the Tutte polynomial TG and the chromatic symmetric function XG. We may also consider XB as a map from the t-extended Hopf algebra G[t] of labelled graphs ... -
A note on intersecting hypergraphs with large cover number
(The Electronic Journal of Combinatorics, 2017-08-11)We give a construction of r-partite r-uniform intersecting hypergraphs with cover number at least r−4 for all but finitely many r. This answers a question of Abu-Khazneh, Barát, Pokrovskiy and Szabó, and shows that a ... -
A note on simplicial cliques
(Elsevier, 2021-09)Motivated by an application in condensed matter physics and quantum information theory, we prove that every non-null even-hole-free claw-free graph has a simplicial clique, that is, a clique K such that for every vertex v ... -
On Aharoni’s rainbow generalization of the Caccetta–Häggkvist conjecture
(Elsevier, 2021-05-01)For a digraph G and v is an element of V(G), let delta(+)(v) be the number of out-neighbors of v in G. The Caccetta-Haggkvist conjecture states that for all k >= 1, if G is a digraph with n = |V(G)| such that delta(+)(v) ... -
On Eulerian orientations of even-degree hypercubes
(Elsevier, 2018-09-01)It is well known that every Eulerian orientation of an Eulerian 2k-edge connected (undirected) graph is strongly k-edge connected. A long-standing goal in the area is to obtain analogous results for other types of connectivity, ... -
On symmetric intersecting families of vectors
(Cambridge University Press, 2021-11)A family of vectors in [k]n is said to be intersecting if any two of its elements agree on at least one coordinate. We prove, for fixed k ≥ 3, that the size of any intersecting subfamily of [k]n invariant under a transitive ... -
Open Shortest Path First Routing Under Random Early Detection
(Wiley, 2018-03-01)In this article, we consider a variant of Open Shortest Path First (OSPF) routing that accounts for Random Early Detection (RED), an Active Queue Management method for backbone networks. In the version of OSPF we consider ... -
Piercing axis-parallel boxes
(The Electronic Journal of Combinatorics, 2018)Let F be a finite family of axis-parallel boxes in Rd such that F contains no k + 1 pairwise disjoint boxes. We prove that if F contains a subfamily M of k pairwise disjoint boxes with the property that for every F E F ... -
Plethysms of Chromatic and Tutte Symmetric Functions
(The Electronic Journal of Combinatorics, 2022)Plethysm is a fundamental operation in symmetric function theory, derived directly from its connection with representation theory. However, it does not admit a simple combinatorial interpretation, and finding coefficients ... -
Polynomial bounds for chromatic number II: Excluding a star-forest
(Wiley, 2022-10)The Gyárfás–Sumner conjecture says that for every forest H, there is a function fH such that if G is H-free then x(G) ≤ fH(w(G)) (where x,w are the chromatic number and the clique number of G). Louis Esperet conjectured ... -
Polynomial bounds for chromatic number. III. Excluding a double star
(Wiley, 2022-10)A “double star” is a tree with two internal vertices. It is known that the Gyárfás-Sumner conjecture holds for double stars, that is, for every double star H, there is a function fH such that if G does not contain H as ... -
Proof of the Kalai-Meshulam conjecture
(Springer Nature, 2020-07-01)Let G be a graph, and let fG be the sum of (−1)∣A∣, over all stable sets A. If G is a cycle with length divisible by three, then fG = ±2. Motivated by topological considerations, G. Kalai and R. Meshulam [8] made the ... -
Pure Pairs VI. Excluding an Ordered Tree.
(Society for Industrial and Applied Mathematics Journal on Discrete Mathematics, 2022-01)A pure pair in a graph G is a pair (Z1,Z2) of disjoint sets of vertices such that either every vertex in Z1 is adjacent to every vertex in Z2, or there are no edges between Z1 and Z2. With Maria Chudnovsky, we recently ... -
Pure pairs. I. Trees and linear anticomplete pairs
(Elsevier, 2020-12-02)The Erdős-Hajnal conjecture asserts that for every graph H there is a constant c > 0 such that every graph G that does not contain H as an induced subgraph has a clique or stable set of cardinality at least |G|c. In this ...