Cordial Labeling of Some Pan Graphs

Abstract

We introduce cordial labeling of path joining two copies m-pan graph, when (m = 3, 4). We also investigated cordial labeling of path union of r-copies of 3-pan graph is cordial only for r ≡ 0, 1,2(mod4). Graph theory plays an important role in the field of mathematics, computer science, operation research, physics, chemistry, biology in general and widely in communication. In the field of graph theory labeling has multiple application like networking, data base management, circuit designing, coding, communication networking. Graph labeling is a function that carries set of vertices or edges to non-negative integers. Throughout the paper K is finite, simple and undirected. We follow Harary [5] for graph theory related basic terminology and notations. The idea of cordial labeling was first invented by Cahit [1] 1987.

Keywords

• 1 Pan graph
• path union of 3-pan graph
• cordial graph

1. Introduction

2. Terminology and Notation

2.1. Definition

Let K = (V, E) be a graph and f : V (K) → {0, 1} is said to be a ( 0−1 ) or a binary vertex labeling of K and the vertex label of K under f is represented by f(l). Consider the induced mapping f*(kl) : E(K) → {0, 1} and derived as f*(kl) = |f(k) − f(l)| where e = kl. We represent, lf (h) as for any vertex v ∈ V (K) such as f(v) = h and ef (h) as for any edge e ∈ E(K) such as f*(e) = h, where h ∈ {0, 1}.

A labeling ( 0 − 1 ) of a graph K is a cordial labeling if following criteria satisfies a) |lf (0) − lf ( 1 )| ≤ 1 b) |ef (0) − ef ( 1 )| ≤ 1. A graph K which preserves cordiality known as a cordial graph. [6]

2.2 Definition

A resultant graph K is called m-pan graph if it is constructed with joining a cycle graph Cm to a pendent vertex.

2.3 Definition

3. Results

Case II For r ≡ 2(mod4)

Proof. We shall denote K as a resultant graph constructed with attaching 2 copies of 3-pan graph by a path of distinct size. Let distinct vertices of 1st and 2nd copies of 3-pan graph be denoted by l1, l2, and l3 and k1, k2 and k3 respectively. Let vertices 1st, 2nd and rth of path Pr be represented by x1, x2, . . . , xr which carries condition as first vertex x1 coincides with l1 and rth vertex, xr coincides with k1. Define a vertex labeling mapping f : V (K) → {0, 1} as given below

Case I for r ≡ 1(mod4)

Above table elaborate labeling pattern of edges. Clearly the condition of cordiality |ef (0) − ef ( 1 )| ≤ 1 is satisfied. Hence, the resultant graph K is cordial. Example 3.1. The cordial labeling resultant graph K under certain condition r ≡ 1(mod4) is constructed with Figure 1.

Theorem 3.2. A graph constructed with attaching 2 copies of 4-pan graph by a path of distinct size preserves cordial labeling.

Proof. We shall denote K as a resultant graph constructed with attaching 2- copies of 4-pan graph by a path of distinct size. Let distinct vertices of 1st and 2nd copies of 4-pan graph be denoted by l1, l2, l3 and l4 and k1, k2, k3 and k4 respectively. Let the vertices 1st, 2nd and rth of path Pr be represented by x1, x2, . . . , xr which carries condition as first vertex x1 coincides with l1 and rth vertex, xr coincides with k1.

Define a vertex labeling mapping f : V (K) → {0, 1} as given below: For r ≡ 0(mod4)

Above table elaborate labeling pattern of edges. Clearly the condition of cordiality |ef (0) − ef ( 1 )| ≤ 1 is satisfied. Hence, the resultant graph K is cordial.

Example 3.2. The cordial labeling of the resultant graph K under certain condition r ≡ 0(mod4) is elaborated by Figure 2. Theorem 3.3. Any path-union of r-copies of 3-pan graph admits cordiality.

Proof. Consider K as a resultant graph constructed with attaching r copies of 3-pan graph by a path of distinct r − 1 size. Let the vertices of 1st, 2nd , . . . , rth copy graph be lh1, lh2, . . . , lhr. Let x1, x2, . . . , xr be the vertices of path Pr with condition x1 = lh1, x2 = lh2, . . . , xr = lhr.

Define a vertex labeling mapping f : V (K) → {0, 1} is stated below Case I: For r ≡ 0(mod4) f(lhq) = 0 ; h = 1(mod4) 1 ; ℎ = 2, 3(4) f(lhq−2) = 0 ; h = 2, 3(mod4) 1 ; h = 1(mod4)

Case II: For r ≡ 1(mod4) f(lhq) =

0 ; h = 1(mod4) 1 ; ℎ = 2, 3(4) f(lhq−2) = f(lhq−3) = Case III: For r ≡ 2(mod4) f(lhq) = 0 ; ℎ = 1(4) 1 ; ℎ = 2, 3(4) f(lhq−2) = f(lhq−3) = 0 ; h = 2, 3(mod4)

1 ; ℎ = 1(4)

Above table elaborate labeling pattern of edges. Clearly the condition of cordiality |ef (0) − ef ( 1 )| ≤ 1 is satisfied. Hence, any path union of r-copies of 3-pan graph admits cordial labeling.

Example 3.3 Cordial labeling of path-union of r-copies of 3-pan graph under certain condition r ≡ 2(mod4) is shown in Figure 3.

4. Conclusion

In this paper we emphasized path joining two copies m-pan graph and path-union of r copies of 3pan graph is cordial. To elaborate several families of graph which satisfies corresponding results is an open problem for the further research. In the field of graph theory labeling has multiple application like networking, data base management, circuit designing, coding, communication networking. Graph theory plays an important role in the field of mathematics, computer science, operation research, physics, chemistry, biology in general and widely in communication.

5. Acknowledgement

Author and co Author would like to thank Cahit. I. for introducing the concept of cordial labeling, using that we have generated cordial labeling of some pan graphs. 6. References

References

[1] I.Cahit , Cordial graphs : A Weaker version of graceful and harmonious graphs . Ars combinatorica , 23 ( 1987 ), 201 - 207 .

[2] I.Cahit , On cordial and 3-equitable labelings of graphs , Utilitas Math, 370 ( 1990 ), 189 - 198 .

[3] D.M. Burton , Elementary Number Theory, Brown Publishers, Seventh Edition , ( 1990 ).

[4] J.A. Gallian , A Dynamic survey of graph labeling , The Electronics Journal of Combinatorics, DS6 , ( 2016 ).

[5] F. Harary , Graph Theory, Addison-Wesley , Reading, Massachusetts,( 1972 ).

[6] R. Varatharajan , S. Navaneethakrishnan , K. Nagrajan , Divisor Cordial Graphs, International J.Math.Combin. , 4 ( 2011 ), 15 - 25 .