Proximity and Remoteness in Graphs: a survey

The proximity $\pi = \pi (G)$ of a connected graph $G$ is the minimum, over all vertices, of the average distance from a vertex to all others. Similarly, the maximum is called the remoteness and denoted by $\rho = \rho (G)$. The concepts of proximity and remoteness, first defined in 2006, attracted the attention of several researchers in Graph Theory. Their investigation led to a considerable number of publications. In this paper, we present a survey of the research work.Comment: arXiv admin note: substantial text overlap with arXiv:1204.1184 by other author

On the Nullity Number of Graphs

The paper discusses bounds on the nullity number of graphs. It is proved in [B. Cheng and B. Liu, On the nullity of graphs. Electron. J. Linear Algebra 16 (2007) 60--67] that $\eta \le n - D$, where $\eta$, n and D denote the nullity number, the order and the diameter of a connected graph, respectively. We first give a necessary condition on the extremal graphs corresponding to that bound, and then we strengthen the bound itself using the maximum clique number. In addition, we prove bounds on the nullity using the number of pendant neighbors in a graph. One of those bounds is an improvement of a known bound involving the domination number

Comparaison automatisée d'invariants en théorie des graphes

Intelligence artificielle et découverte automatisée -- De autographix à autographix 2 -- Comparaison systématique de quelques invariants

Some properties of the distance Laplacian eigenvalues of a graph

summary:The distance Laplacian of a connected graph $G$ is defined by $\mathcal {L} = {\rm Diag(Tr)}- \mathcal {D}$, where $\mathcal {D}$ is the distance matrix of $G$, and ${\rm Diag(Tr)}$ is the diagonal matrix whose main entries are the vertex transmissions in $G$. The spectrum of $\mathcal {L}$ is called the distance Laplacian spectrum of $G$. In the present paper, we investigate some particular distance Laplacian eigenvalues. Among other results, we show that the complete graph is the unique graph with only two distinct distance Laplacian eigenvalues. We establish some properties of the distance Laplacian spectrum that enable us to derive the distance Laplacian characteristic polynomials for several classes of graphs

Recherche à voisinage variable de graphes extrémaux 13. à propos de la maille

Le système AutoGraphiX (AGX1 et AGX2) permet, parmi d'autres fonctions, la génération automatique de conjectures en théorie des graphes et, dans une version plus récente, la preuve automatique de conjectures simples. Afin d'illustrer ces fonctions et le type de résultats obtenus, nous étudions systématiquement ici des conjectures obtenues par ce système et de la forme $\underline{b}_{n} \, \le \, g \, \oplus \, i \, \le \, \overline{b}_{n}$ où g désigne la maille (ou longueur du plus petit cycle) du graphe G=(V, E), i un autre invariant choisi parmi le nombre de stabilité, le rayon, le diamètre, le degré minimum, moyen ou maximum, $\underline{b}_{n}$ et $\overline{b}_{n}$ des fonctions de l'ordre n = |V| de G les meilleures possibles, enfin $\oplus$ correspond à une des opérations +,-,×,/. 48 telles conjectures sont obtenues: les plus simples sont démontrées automatiquement et les autres à la main. De plus 12 autres conjectures ouvertes et non encore étudiées sont soumises aux lecteurs

Some properties of the distance Laplacian eigenvalues of a graph

summary:The distance Laplacian of a connected graph $G$ is defined by $\mathcal {L} = {\rm Diag(Tr)}- \mathcal {D}$, where $\mathcal {D}$ is the distance matrix of $G$, and ${\rm Diag(Tr)}$ is the diagonal matrix whose main entries are the vertex transmissions in $G$. The spectrum of $\mathcal {L}$ is called the distance Laplacian spectrum of $G$. In the present paper, we investigate some particular distance Laplacian eigenvalues. Among other results, we show that the complete graph is the unique graph with only two distinct distance Laplacian eigenvalues. We establish some properties of the distance Laplacian spectrum that enable us to derive the distance Laplacian characteristic polynomials for several classes of graphs

On a conjecture about the Randić index

AbstractA conjecture of Delorme, Favaron and Rautenbach [On the Randić index, Discrete Math. 257 (2002) 29–38] about the Randić index of a graph, in relation to its order and minimum degree, is refuted by the AutoGraphiX 2 system. Moreover, a modified conjecture is derived from presumably extremal graphs obtained with that system