Domination subdivision and domination multisubdivision numbers of graphs

The domination subdivision number sd(G) of a graph G is the minimum number of edges that must be subdivided (where an edge can be subdivided at most once) in order to increase the domination number of G. It has been shown [10] that sd(T)<=3 for any tree T. We prove that the decision problem of the domination subdivision number is NP-complete even for bipartite graphs. For this reason we define the domination multisubdivision number of a nonempty graph G as a minimum positive integer k such that there exists an edge which must be subdivided k times to increase the domination number of G. We show that msd(G)<=3 for any graph G. The domination subdivision number and the domination multisubdivision number of a graph are incomparable in general, but we show that for trees these two parameters are equal. We also determine the domination multisubdivision number for some classes of graphs.

Graphs with equal domination and certified domination numbers

M. Dettlaff , M. Lemańska , J. Topp, M. Miotk, R. Ziemann, P. Żyliński – Opuscula Mathematica – 2019
A setDof vertices of a graphG= (VG,EG) is a dominating set ofGif every vertexinVG−Dis adjacent to at least one vertex inD. The domination number (upper dominationnumber, respectively) ofG, denoted byγ(G) (Γ(G), respectively), is the cardinality ofa smallest (largest minimal, respectively) dominating set ofG. A subsetD⊆VGis calleda certified dominating set ofGifDis a dominating set ofGand every vertex inDhas eitherzero or at least two neighbors inVG−D. The cardinality of a smallest (largest minimal,respectively) certified dominating set ofGis called the certified (upper certified, respectively)domination number ofGand is denoted byγcer(G) (Γcer(G), respectively). In this paperrelations between domination, upper domination, certified domination and upper certifieddomination numbers of a graph are studied

On the super domination number of lexicographic product graphs

M. Dettlaff , M. Lemańska , J. Rodríguez-Velázquez, R. Zuazua – DISCRETE APPLIED MATHEMATICS – 2019
The neighbourhood of a vertexvof a graphGis the setN(v) of all verticesadjacent tovinG. ForD⊆V(G) we defineD=V(G)\D. A setD⊆V(G) is called a super dominating set if for every vertexu∈D, there existsv∈Dsuch thatN(v)∩D={u}. The super domination number ofGis theminimum cardinality among all super dominating sets inG. In this article weobtain closed formulas and tight bounds for the super dominating number oflexicographic product graphs in terms of invariants of the factor graphs involvedin the product. As a consequence of the study, we show that theproblem offinding the super domination number of a graph is NP-Hard (16) (PDF) On the super domination number of lexicographic product graphs. Available from: https://www.researchgate.net/publication/315382754_On_the_super_domination_number_of_lexicographic_product_graphs [accessed Jul 28 2020].

Certified domination

M. Dettlaff , M. Lemańska , J. Topp, R. Ziemann, P. Żyliński – AKCE International Journal of Graphs and Combinatorics – 2018
Imagine that we are given a set D of officials and a set W of civils. For each civil x ∈ W, there must be an official v ∈ D that can serve x, and whenever any such v is serving x, there must also be another civil w ∈ W that observes v, that is, w may act as a kind of witness, to avoid any abuse from v. What is the minimum number of officials to guarantee such a service, assuming a given social network? In this paper, we introduce the concept of certified domination that models the aforementioned problem. Specifically, a dominating set D of a graph G = (VG, EG) is said to be certified if every vertex in D has either zero or at least two neighbours in VG \ D. The cardinality of a minimum certified dominating set in G is called the certified domination number of G. Herein, we present the exact values of the certified domination number for some classes of graphs as well as provide some upper bounds on this parameter for arbitrary graphs. We then characterise a wide class of graphs with equal domination and certified domination numbers and characterise graphs with large values of certified domination numbers. Next, we examine the effects on the certified domination number when the graph is modified by deleting/adding an edge or a vertex. We also provide Nordhaus–Gaddum type inequalities for the certified domination number.

Coronas and Domination Subdivision Number of a Graph

In this paper, for a graph G and a family of partitions P of vertex neighborhoods of G, we define the general corona G ◦P of G. Among several properties of this new operation, we focus on application general coronas to a new kind of characterization of trees with the domination subdivision number equal to 3.

Total domination in versus paired-domination in regular graphs

A subset S of vertices of a graph G is a dominating set of G if every vertex not in S has a neighbor in S, while S is a total dominating set of G if every vertex has a neighbor in S. If S is a dominating set with the additional property that the subgraph induced by S contains a perfect matching, then S is a paired-dominating set. The domination number, denoted γ(G), is the minimum cardinality of a dominating set of G, while the minimum cardinalities of a total dominating set and paired-dominating set are the total domination number, \gt(G), and the paired-domination number, \gp(G), respectively. For k ≥ 2, let G be a connected k-regular graph. It is known [Schaudt, Total domination versus paired domination, Discuss. Math. Graph Theory 32 (2012) 435--447] that \gpr(G)/γt(G) \le (2 k)/(k + 1). In the special case when k = 2, we observe that \gpr(G)/γt(G) \le 4/3, with equality if and only if G \cong C5. When k = 3, we show that \gpr(G)/γt(G) \le 3/2, with equality if and only if G is the Petersen graph. More generally for k ≥ 2, if G has girth at least 5 and satisfies \gpr(G)/γt(G) = (2 k)/(k + 1), then we show that G is a diameter-2 Moore graph. As a consequence of this result, we prove that for k ≥ 2 and k \ne 57, if G has girth at least 5, then \gpr(G)/γt(G) \le (2 k)/(k + 1), with equality if and only if k=2 and G \cong C5 or k = 3 and G is the Petersen graph.

Total Domination Versus Domination in Cubic Graphs

A dominating set in a graph G is a set S of vertices of G such that every vertex not in S has a neighbor in S. Further, if every vertex of G has a neighbor in S, then S is a total dominating set of G. The domination number,γ(G), and total domination number, γ_t(G), are the minimum cardinalities of a dominating set and total dominating set, respectively, in G. The upper domination number, \Gamma(G), and the upper total domination number, \Gamma_t(G), are the maximum cardinalities of a minimal dominating set and total dominating set, respectively, in G. It is known that γ_t(G)/γ (G)≤2 and \Gamma_t(G)/ \Gamma(G)≤2 for all graphs G with no isolated vertex. In this paper we characterize the connected cubic graphs G satisfying γ_t(G)/γ (G)=2, and we characterize the connected cubic graphs G satisfying \Gamma_t(G)/ \Gamma(G)=2.

Edge subdivision and edge multisubdivision versus some domination related parameters in generalized corona graphs

Given a graph G= (V, E), the subdivision of an edge e=uv∈E(G) means the substitution of the edge e by a vertex x and the new edges ux and xv. The domination subdivision number of a graph G is the minimum number of edges of G which must be subdivided (where each edge can be subdivided at most once) in order to increase the domination number. Also, the domination multisubdivision number of G is the minimum number of subdivisions which must be done in one edge such that the domination number increases. Moreover, the concepts of paired domination and independent domination subdivision (respectively multisubdivision) numbers are defined similarly. In this paper we study the domination, paired domination and independent domination (subdivision and multisubdivision) numbers of the generalized corona graphs.

Some variations of perfect graphs

M. Dettlaff , M. Lemańska , G. Semanišin, R. Zuazua – Discussiones Mathematicae Graph Theory – 2016
We consider (ψk−γk−1)-perfect graphs, i.e., graphs G for which ψk(H) =γk−1(H) for any induced subgraph H of G, where ψk and γk−1 are the k -path vertex cover number and the distance (k−1)-domination number, respectively. We study (ψk−γk−1)-perfect paths, cycles and complete graphs for k≥2. Moreover, we provide a complete characterisation of (ψ2−γ1)-perfect graphs describing the set of its forbidden induced subgraphs and providing the explicit characterisation of the structure of graphs belonging to this family.