A set of planar graphs share a simultaneous embedding if they can be drawn on the same vertex set V in the Euclidean plane without crossings between edges of the same graph. Fixed edges are common edges between graphs that share the same simple curve in the simultaneous drawing. Determining in polynomial time which pairs of graphs share a simultaneous embedding with fixed edges (SEFE) has been ...

In this paper, we are studying vertex-magic total labelings (VMTLs) of simple graphs. By now much is known about methods for constructing VMTLs for regular graphs. Here we are studying non-regular graphs. We show how to construct labelings for several families of non-regular graphs, including graphs formed as the disjoint union of two other graphs already possessing VMTLs. We focus on condition...

A 2-subcolouring of a graph is a partition of the vertices into two subsets, each inducing a P3-free graph, i.e., a disjoint union of cliques. We give the first polynomial time algorithm to test whether a chordal graph has a 2-subcolouring. This solves (for two colours) an open problem of Broersma, Fomin, Nešetřil, and Woeginger, who gave an O(n) time algorithm for interval graphs. Our algorith...

The paper generalizes the notion of locating-chromatic number of a graph such that it can be applied to disconnected graphs as well. In this sense, not all the graphs will have finite locating-chromatic numbers. We derive conditions under which a graph has a finite locating-chromatic number. In particular, we determine the locatingchromatic number of a uniform linear forest, namely a disjoint u...

A relational structure A satisfies the P(n, k) property if whenever the vertex set of A is partitioned into n nonempty parts, the substructure induced by the union of some k of the parts is isomorphic to A. The P(2, 1) property is just the pigeonhole property, (P), introduced by Cameron, and studied by Bonato, Delić and Cameron. We classify the countable graphs, tournaments, and oriented graphs...

Polar graphs generalise bipartite, cobipartite, and split graphs, and they constitute a special type of matrix partitions. A graph is polar if its vertex set can be partitioned into two, such that one part induces a complete multipartite graph and the other part induces a disjoint union of complete graphs. Deciding whether a given arbitrary graph is polar, is an NP-complete problem. Here we sho...

The graph G of order n is an L-borderenergetic which means it has the same Laplacian energy as complete Kn. In this paper, we find that combination bipartite graphs and stars can construct infinite numbers classes graphs. We give two Lborderenergetic under operators union, join their mixed. This research could provide experience for further study structural characteristics

Polar graphs are a natural extension of some classes of graphs like bipartite graphs, split graphs and complements of bipartite graphs. A graph is (s, k)-polar if there exists a partition A, B of its vertex set such that A induces a complete s-partite graph (i.e., a collection of at most s disjoint stable sets with complete links between all sets) and B a disjoint union of at most k cliques (i....