Diametral paths in extended transformation graphs

In a graph, diametral path is shortest path between two vertices which has length equal to diameter of the graph. Number of diametral paths plays an important role in computer science and civil engineering. In this paper, we introduce the concept of extended transformation graphs. There are 64 extended transformation graphs. We obtain number of diametral paths in some of the extended transformation graphs and we also study the semi-complete property of these extended transformation graphs. Further, a program is given for obtaining number of diametral paths

Algorithms for rainbow vertex colouring diametral path graphs

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On the Complexity of Rainbow Vertex Colouring Diametral Path Graphs

Given a graph and a colouring of its vertices, a rainbow vertex path is a path between two vertices such that all the internal nodes of the path are coloured distinctly. A graph is rainbow vertex-connected if between every pair of vertices in the graph there exists a rainbow vertex path. We study the problem of deciding whether a given graph can be coloured using k or less colours such that it is rainbow vertex-connected. Note that every graph G needs at least diam(G)-1 colours to be rainbow vertex connected. Heggernes et al. [MFCS, 2018] conjectured that if G is a graph in which every induced subgraph has a dominating diametral path, then G can always be rainbow vertex coloured with diam(G)-1 many colours. In this work, we confirm their conjecture for chordal, bipartite and claw-free diametral path graphs. We complement these results by showing the conjecture does not hold if the condition on every induced subgraph is dropped. In fact we show that, in this case, even though diam(G) many colours are always enough, it is NP-complete to determine whether a graph with a dominating diametral path of length three can be rainbow vertex coloured with two colours

Minimum Breadth of a Graph

Breadth of a graph as the maximum of heights taken over all diametral paths is investigated in [3, 4], where height is taken by placing each diametral path on level y = 0 and placing uniquely the rest of the vertices on levels y = 1, 2…k keeping adjacency intact. A parameter minimum breadth is introduced as minimum of heights with respect to all diametral paths. A few results on minimum breadth in certain classes of graphs are presented. Also the bounds on number of vertices and edges for graphs of known diameter and minimum breadth are proposed