International Journal of Advanced Scientific Research and Management, Volume 3 Issue 8, Aug 2018 www.ijasrm.com

ISSN 2455-6378

Triple Connected Line Domination Number For Some Standard And Special Graphs

A.Robina Tony1, Dr. A.Punitha Tharani2

1 Research Scholar (Register Number: 12519), Department of Mathematics, St.Mary’s College(Autonomous), Thoothukudi – 628 001, Tamil Nadu, India, Affiliated to Manonmaniam Sundaranar University, Abishekapatti, Tirunelveli – 627 012, Tamil Nadu, India

2 Associate Professor, Department of Mathematics, St.Mary’s College(Autonomous), Thoothukudi – 628 001, Tamil Nadu, India, Affiliated to Manonmaniam Sundaranar University, Abishekapatti, Tirunelveli - 627 012, Tamil Nadu, India

Abstract domination, the concept of edge The concept of triple connected graphs with real life domination was introduced by Mitchell and application was introduced by considering the Hedetniemi. A set F of edges in a graph G is existence of a path containing any three vertices of a called an edge dominating set if every edge in E graph G. A subset S of V of a non - trivial graph G is – F is adjacent to at least one edge in F. The said to be a triple connected dominating set, if S is a dominating set and the induced subgraph is edge domination number γ '(G) of G is the triple connected. The minimum cardinality taken minimum cardinality of an edge dominating set over all triple connected dominating set is called the of G. An edge dominating set F of a graph G is triple connected domination number and is denoted a connected edge dominating set if the edge by γtc(G). A subset D of E of a non- trivial graph G is induced subgraph 〈F〉 is connected. The said to be a triple connected line dominating set, if D connected edge domination number γ'c(G) of G is an edge dominating set and the edge induced is the minimum cardinality of a connected edge subgraph is triple connected. The minimum dominating set of G. The concept of connected cardinality taken over all triple connected line edge domination was introduced by Kulli and dominating set is called the triple connected line ’ Sigarkanti. The concept of triple connected domination number and is denoted by γtcl (G). In this paper, we determine this number for some standard graphs with real life application was introduced and special graphs. by considering the existence of a path containing any three vertices of a graph G. G. Keywords: Triple connected, Triple connected Mahadevan et. al., introduced the concept of domination number of a graph, Triple connected line triple connected domination number of a graph. domination number of a graph. A subset S of V of a nontrivial connected graph G is said to be triple connected dominating set, 1. Introduction if S is a dominating set and the induced sub graph is triple connected. The minimum All graphs considered here are finite, undirected cardinality taken over all triple connected without loops and multiple edges. Unless and dominating sets is called the triple connected otherwise stated, the graph G = (V, E) domination number and is denoted by γtc. A considered here have p = vertices and q = subset D of E of a nontrivial connected graph G edges. A set S of vertices in a graph G is is said to be a triple connected line dominating called a dominating set if every vertex in V – S set, if D is an edge dominating set and the edge is adjacent to some vertex in S. The domination induced subgraph is triple connected. The number γ (G) of G is the minimum cardinality minimum cardinality taken over all triple of a dominating set of G. As an analogy to connected line dominating sets is called the 107

International Journal of Advanced Scientific Research and Management, Volume 3 Issue 8, Aug 2018 www.ijasrm.com

ISSN 2455-6378

triple connected line domination number of G ’ ’ and is denoted by γtcl (G). γtcl (Cp) =

2. Exact value for some standard graphs Proof Let Cp be a cycle of order p ≥ 3 and let D be a

2.1. Proposition triple connected line dominating set of Cp

For any path Pp of order p ≥ 3, Case (i) p=3 Then = P3 which is triple ’ ’ γtcl (Pp) = connected. Hence, γtcl (Cp) = = 2.

Case (ii) p≥ 4 The only connected subgraphs of any cycle are paths, which are triple connected. If Proof = 2, then D is an edge dominating set Let Pp be a path of order p ≥ 3 and let D and and = Pp-2 be a triple connected line dominating set of Pp.

Case (i) p < 5 Hence, D is a triple connected line Since the existence of a triple connected dominating set. If > 2, then take any line dominating set of a connected graph G three consecutive edges x, y, z . The ’ edge y is not dominated by any edge in D since implies that γtcl (G) ≥ 2, we need to show the the only neighbors of y are x and z. Therefore, existence of such a set D. For P3 it is obvious. exactly two edges can be removed from Cp to For P4, take any two consecutive edges to be in D. Therefore, D is an edge dominating set and obtain a triple connected line dominating set of minimum cardinality. = P3 which is triple connected. Hence, ’ 2.3. Proposition γtcl (Pp) = = 2, if p < 5. For the star graph K1,p-1 of order p ≥ 3, we have ’ Case (ii) p ≥ 5 γtcl (K1,p-1) = 2 The only connected subgraph of any path are paths, which are triple connected. If Proof = 2, then there are two subcases to be Let K1,p-1 be a star of order p ≥ 3. Let v0 considered. be the central vertex of K1,p-1 and let ei, ej be any Subcase 1 two edges incident on the root vertex of K1,p-1. If E – D contains a pendant edge and its Then, the set D = {ei, ej} is a triple connected neighbor, the pendant edge is not dominated by line dominating set of K1,p-1 of minimum ’ any edge in D, and hence D is not an edge cardinality. Hence, γtcl (K1,p-1) = = 2. dominating set. 2.4. Proposition Subcase 2 If E – D contains the two pendant For any bistar Bm,n of order p, where m + n + 2 edges, then D is an edge dominating set and and ’ = p, m, n ≥ 1, and p ≥ 4, we have γtcl (Bm,n) = 2. = Pp-2 Hence D is a triple connected line dominating set. Proof:

Let Bm,n be a bistar of order p, where m 2.2. Proposition + n + 2 = p, m,n ≥ 1, and p ≥ 4. If the edge connecting the root vertices of the bistar is in D, For any cycle Cp of order p ≥ 3, then D is already an edge dominating set. Thus,

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to obtain a triple connected line dominating set, we only need to add one more edge to D. ’ For the Truncated G, γtcl (G) = ’ Hence, = P3 and γtcl (Bp;q) = = 2. 8. Here D = {e1, e2, e5, e8, e10, e14, e15, e16 } is a minimum triple connected line 3. Triple connected line domination domination number of a graph. number for some special graphs

3.1. The Franklin graph is a 3- 3.3. The Herschel graph is a bipartite with 12 vertices and 18 edges as shown in undirected graph with 11 vertices and 18 the Fig.1 edges as shown in Fig 3, the smallest non hamiltonian . It is named after British astronomer Alexander Stewart Herschel

Fig. 1

’ For the Franklin graph G, γtcl (G) = 9 . Here D =

{e3, e4, e6, e8, e9, e12, e14, e16 , e18} is a minimum triple connected line domination number of a graph. 3.2. The Truncated Tetrahedron is an

Archimedean solid. It has 4 regular hexagonal faces, 4 regular triangular faces, 12 vertices and Fig. 3 18 edges as shown in Fig.2 Archimedean solid ’ means one of 13 possible solids whose faces are For the Herschel graph G, γtcl (G) = 7. Here all regular polygons whose polyhedral angles D = {e1, e2, e3, e4, e5, e6, e7} is a minimum are all equal. triple connected line domination number of a graph

3.4. The Golomb graph is a unit distance graph discovered around 1960 – 1965 by Golomb with 10 vertices and 18 edges as shown in the Fig 4

Fig. 2

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4.Conclusion

In this paper we provided the triple connected line domination number of some special and standard graphs. Further, the bounds for general graph and its relationship with other graph theoretical parameters can also be investigated.

References Fig. 4 ’ [1] John Adrian Bondy, Murty For the Golomb graph G, γ (G) = 7 . Here tcl U.S.R.(2009): , D = {e1, e4, e7, e9, e10, e11, e12} is a minimum Springer, 2008. triple connected line domination number of [2] V.R.Kulli, College Graph a graph. Theory,Vishwa International Publications,Gulbarga, India (2012). 3.5 The Goldner–Harary graph is a simple [3] V.R.Kulli, Theory of undirected graph with 11 vertices and 27 Domination in Graphs, Vishwa edges as shown in Fig 5. It is named after A. International Publications, Gulbarga, Goldner and Frank Harary, who proved in India (2010). [4] V.R.Kulli and S.C.Sigarakanti, 1975 that it was the smallest non The connected edge domination hamiltonian maximal . number of a graph, Technical Report 8801, Dept Math. Gulbarga University, (1988). [5] G. Mahadevan, A. Selvam, J. Paulraj Joseph and, T. Subramanian, Triple connected domination number of a graph,International Journal of Mathematical Combinatorics, Vol.3 (2012), 93 - 104. [6] S. L. Mitchell and S. T. Hedetniemi,Edge domination in trees. Congr. Numer.19 (1997) 489-

509. Fig. 5 [7] Paulraj Joseph J., Angel Jebitha M.K.,Chithra Devi P. and Sudhana ’ For the Goldner–Harary graph G, γtcl (G) = G. (2012):Triple connected graphs, 5. Here D = {e8, e15, e16, e17, e27} is a Indian Journal of Mathematics and minimum triple connected line domination Mathematical Sciences, ISSN 0973- number of a graph. 3329 Vol. 8,No. 1: 61-75. [8] Teresa W. Haynes, Stephen T. Hedetniemi and Peter J. Slater (1998):Fundamentals of domination in graphs,Marcel Dekker, New York.

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