Hamiltonian Cycles in Critical Graphs with Large Maximum Degree

Given a simple graph $G$, denote by $\Delta(G)$, $\delta(G)$, and $\chi'(G)$ the maximum degree, the minimum degree, and the chromatic index of $G$, respectively. We say $G$ is $\Delta$-critical if $\chi'(G)=\Delta(G)+1$ and $\chi'(H)\le \Delta(G)$ for every proper subgraph $H$ of $G$, and $G$ is overfull if $|E(G)|>\Delta(G) \lfloor |V(G)|/2 \rfloor$. Since a maximum matching in $G$ can have size at most $\lfloor |V(G)|/2 \rfloor$, it follows that $\chi'(G) = \Delta(G) +1$ if $G$ is overfull. Conversely, let $G$ be a $\Delta$-critical graph. The well known overfull conjecture of Chetwynd and Hilton asserts that $G$ is overfull provided $\Delta(G) > |V(G)|/3$. In this paper, we show that any $\Delta$-critical graph $G$ is overfull if $\Delta(G) - 7\delta(G)/4\ge (3|V(G)|-17)/4$.

It is proved that a planar graph with maximum degree Δ ≥ 11 has total (vertex-edge) chromatic number $Delta; + 1. © 1997 John Wiley & Sons, Inc. J Graph Theory 26: 53–59, 1997

Densely connected sub-Gaussian linear structural equation model learning via ℓ1- and ℓ2-regularized regressions

Improved square coloring of planar graphs

Recent experiments have shown ASP solvers to run significantly faster on ground programs of small treewidth. If possible, it may therefore be beneficial to write a non-ground ASP encoding such that grounding it together with an input of small treewidth leads to a propositional program of small treewidth. In this work, we prove that a class of non-ground programs called guarded ASP guarantees this property. Guarded ASP is a subclass of the recently proposed class of connection-guarded ASP, which is known to admit groundings whose treewidth depends on both the treewidth and the maximum degree of the input. Here we show that this dependency on the maximum degree cannot be dropped. Hence, in contrast to connection-guarded ASP, guarded ASP promises good performance even if the input has large maximum degree.

An adjacent vertex distinguishing total coloring of a graph G is a proper total coloring of G such that any pair of adjacent vertices have distinct sets of colors. The minimum number of colors needed for an adjacent vertex distinguishing total coloring of G is denoted by $\chi''_{a}(G)$ . In this paper, we characterize completely the adjacent vertex distinguishing total chromatic number of planar graphs G with large maximum degree Δ by showing that if Δ?14, then $\varDelta+1\leq \chi''_{a}(G)\leq \varDelta+2$ , and $\chi''_{a}(G)=\varDelta+2$ if and only if G contains two adjacent vertices of maximum degree.

In graph theory, Hamiltonian path refers to the path that visits each vertex exactly once. In this paper, we designed a method to generate random Hamiltonian path within digital images, which is equivalent to permutation in image encryption. By these means, building a Hamiltonian path across bit planes can shuffle the distribution of the pixel’s bits. Furthermore, a similar thought can be applied for the substitution of pixel’s grey levels. To ensure the randomness of the generated Hamiltonian path, an adjusted Bernoulli map is proposed. By adopting these novel techniques, a bit-level image encryption scheme was devised. Evaluation of simulation results proves that the proposed scheme reached fair performance. In addition, a common flaw in calculating correlation coefficients of adjacent pixels was pinpointed by us. After enhancement, correlation coefficient becomes a stricter criterion for image encryption algorithms.

Theoretical aspects of equitable partition of networks into sparse modules

Incidence coloring of Mycielskians with fast algorithm

On Hamiltonicity of [formula omitted]-free graphs

A graph is called $k$ -critical if its chromatic number is $k$ but every proper subgraph has chromatic number less than $k$ . An old and important problem in graph theory asks to determine the maximum number of edges in an $n$ -vertex $k$ -critical graph. This is widely open for every integer $k\geq 4$ . Using a structural characterisation of Greenwell and Lovász and an extremal result of Simonovits, Stiebitz proved in 1987 that for $k\geq 4$ and sufficiently large $n$ , this maximum number is less than the number of edges in the $n$ -vertex balanced complete $(k-2)$ -partite graph. In this paper, we obtain the first improvement in the above result in the past 35 years. Our proofs combine arguments from extremal graph theory as well as some structural analysis. A key lemma we use indicates a partial structure in dense $k$ -critical graphs, which may be of independent interest.

Bunaken sea is one of the fisheries source for Manado and around it. But unfortunately, some studies have shown that the coral reefs in some parts of Bunaken Sea have been deteriorating. Some of the causes are coral retrieval, illegal fishing using explosive and poison, marine pollution, and sea temperature increase. Deteriorated reef can be recognized through the color becomes white or known as coral bleaching. In order to preserve coral reefs, there are some factors that can be learned. One of the factors is the location of the healthy coral reefs and can produce coral larval to help recovery process of the deteriorated reefs. Based on some research, coral larval dispersion will be modelled using Graph Theory that is objects connectivity, especially the Hamiltonian Path. Reef spots are represented by vertices and dispersion paths are represented by edges. Based on research, the first location that must be conserved is M23 because it gives good impact and has high possibilities to help recovery of the other 16 locations. Research about determine the coral larval dispersion path can be used to help coral reef conservation to minimize the time and budget, also can support the development of marine, fisheries, and tourism.

Finding general conditions which ensure that a graph is Hamiltonian is a central topic in graph theory. An old and well known conjecture in the area states that any $d$-regular $n$-vertex graph $G$ whose second largest eigenvalue in absolute value $\lambda(G)$ is at most $d/C$, for some universal constant $C>0$, has a Hamilton cycle. We obtain two main results which make substantial progress towards this problem. Firstly, we settle this conjecture in full when the degree $d$ is at least a small power of $n$. Secondly, in the general case we show that $\lambda(G) \leq d/ C(\log n)^{1/3}$ implies the existence of a Hamilton cycle, improving the 20-year old bound of $d/ \log^{1-o(1)} n$ of Krivelevich and Sudakov. We use in a novel way a variety of methods, such as a robust P\'osa rotation-extension technique, the Friedman-Pippenger tree embedding with rollbacks and the absorbing method, combined with additional tools and ideas. Our results have several interesting applications, giving best bounds on the number of generators which guarantee the Hamiltonicity of random Cayley graphs, which is an important partial case of the well known Hamiltonicity conjecture of Lov\'asz. They can also be used to improve a result of Alon and Bourgain on additive patterns in multiplicative subgroups.

We consider the standard random geometric graph process in which n vertices are placed at random on the unit square and edges are sequentially added in increasing order of edge-length. For fixed k⩾1, weprove that the first edge in the process that creates a k-connected graph coincides a.a.s. with the first edge that causes the graph to contain k/2 pairwise edge-disjoint Hamilton cycles (for even k), or (k−1)/2 Hamilton cycles plus one perfect matching, all of them pairwise edge-disjoint (for odd k). This proves and extends a conjecture of Krivelevich and M **image**ler. In the special case when k = 2, our result says that the first edge that makes the random geometric graph Hamiltonian is a.a.s. exactly the same one that gives 2-connectivity, which answers a question of Penrose. (This result appeared in three independent preprints, one of which was a precursor to this article.) We prove our results with lengths measured using the lp norm for any p>1, and we also extend our result to higher dimensions. © 2011 Wiley Periodicals, Inc. J Graph Theory 68:299-322, 2011 © 2011 Wiley Periodicals, Inc.

Hamiltonian cycles play an important role in graph theory and data mining applications. Two Hamiltonian cycles that don’t have an edge in common are known as edge-disjoint Hamiltonian cycles (EDHCs). EDHCs are useful in computer networks. They have found applications in improving network capacity, fault-tolerance and collusion resistant mining algorithms. This paper extends previous work on collusion resistance capability of data mining algorithms. We first propose a new trust model for network computers. We then use this model as a basis to improve the collusion resistance capability of data mining algorithms. We use a performance metric to quantify the improvement.