In 1966, Gallai conjectured that all the longest paths of a connected graph have a common vertex. Zamfirescu conjectured that the smallest counterexample to Gallai’s conjecture is a graph on 12 vertices. We prove that Gallai’s conjecture is true for every connected graph with , which implies that Zamfirescu’s conjecture is true.
The spectral radius of a graph is defined by that of its unoriented Laplacian matrix. In this paper, we determine the unicyclic graphs respectively with the third and the fourth largest spectral radius among all unicyclic graphs of given order.
A graph G is called k-ordered if for every sequence of k distinct vertices there is a cycle traversing these vertices in the given order. In the present paper we consider two novel generalizations of this concept, k-vertex-edge-ordered and strongly k-vertex-edge-ordered. We prove the following results for a chordal graph G: (a) G is (2k-3)-connected if and only if it is k-vertex-edge-ordered (k ≥ 3). (b) G is (2k-1)-connected if and only if it is strongly k-vertex-edge-ordered...
The reverse Wiener index of a connected graph is defined as where is the number of vertices, is the diameter, and is the Wiener index (the sum of distances between all unordered pairs of vertices) of . We determine the -vertex non-starlike trees with the first four largest reverse Wiener indices for , and the -vertex non-starlike non-caterpillar trees with the first four largest reverse Wiener indices for .
Dans cet article, nous essayons de faire le point sur les résultats concernant les aspects combinatoires et algorithmiques des ordres médians et des ordres de Slater des tournois. La plupart des résultats recensés sont tirés de différentes publications ; plusieurs sont originaux.
The orientation distance graph 𝓓ₒ(G) of a graph G is defined as the graph whose vertex set is the pair-wise non-isomorphic orientations of G, and two orientations are adjacent iff the reversal of one edge in one orientation produces the other. Orientation distance graphs was introduced by Chartrand et al. in 2001. We provide new results about orientation distance graphs and simpler proofs to existing results, especially with regards to the bipartiteness of orientation distance graphs and the representation...
We provide the list of all paths with at most arcs with the property that if a graph admits an orientation such that one of the paths in our list admits no homomorphism to , then is -colourable.
We obtain some improved upper and lower bounds on the oriented chromatic number for different classes of products of graphs.