# Sum Divisor Cordial Labeling of Herschel Graph

## Full text

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Vol. 14, No. 3, 2017, 465-472

ISSN: 2279-087X (P), 2279-0888(online) Published on 30 October 2017

www.researchmathsci.org

DOI: http://dx.doi.org/10.22457/apam.v14n3a14

465

Annals of

## Sum Divisor Cordial Labeling of Herschel Graph

A.Sugumaran1 and K.Rajesh2

Department of Mathematics, Government Arts College Tiruvannamalai-606603,Tamilnadu, India.

1

E-mail:sugumaranaruna@gmail.com

2

E-mail: k.rajesh3429@gmail.com.

Received 2 October 2017; accepted 25 October 2017

Abstract. A sum divisor cordial labeling of a graph

### G

with vertex set V G( ) is a bijection f from V G( ) to {1, 2,...,|V G( ) |} such that each edge uv assigned the label 1 if 2 divides f u( )+ f v( ) and

### 0

otherwise. Further, the number of edges labeled with

### 0

and the number of edges labeled with 1 differ by at most 1. A graph with a sum divisor cordial labeling is called a sum divisor cordial graph. In this paper, we prove that Herschel graph Hs, fusion of any two adjacent vertices of degree 3 in a Herschel graph

s

H , duplication of any vertex of degree 3 in a Herschel graph Hs, switching of a

central vertex in the Herschel graph Hs, path union of two copies of Hs are sum divisor cordial graphs.

Keywords: Divisor cordial labeling, sum divisor cordial labeling, fusion, duplication, switching, path union.

AMS Mathematics Subject Classification (2010): 05C78 1. Introduction

By a graph, we mean a finite undirected graph without loops or multiple edges. For standard terminology and notations related to graph theory we refer to Harary . A labeling of graph is a map that carries the graph elements to the set of numbers, usually to the set of non-negative or positive integers. If the domain is the set of edges, then we speak about edge labeling. If the labels are assigned to both vertices and edges, then the labeling is called total labeling. Cordial labeling is extended to divisor cordial labeling, prime cordial labeling, total cordial labeling, Fibonacci cordial labeling etc.

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For dynamic survey of

and Patrick  introduced the concept of sum divisor cordial labeling Rajesh proved that Swastik graph

n

Sw , cycle of k copies of Swastik graph Petersen graph are sum divisor cordial graphs

Theta graph and some graph operations in Theta graph are sum divisor cordial graphs. Ganesan and Balamuruga

primary objective of this paper is to prove the Herschel

in Herschel graph namely fusion, duplication, switching of a central vertex, path two copies of Herschel graphs are sum divisor cordial graphs.

Definition 1.1.  : ( ) {1, 2,...,| ( ) |}

f V GV G

either f u( ) | f v or ( ) |( ) f v f v( ) divisor cordial labeling

labeling is called a divisor cordial graph

Definition 1.2.  : ( ) {1, 2,...,| ( ) |}

f V GV G

either 2 | ( ( )f u + f v( )) sum divisor cordial labeling

divisor cordial labeling is called a

Definition 1.3. A Herschel graph and 18 edges.

In this paper, we always

the above Figure 1, unless or other

Definition 1.4. Let

### u

and

constructed by fusing (identifying) two vertices

For dynamic survey of various graph labeling, we refer to Gallian  introduced the concept of sum divisor cordial labeling.

roved that Swastik graph Swn, path union of finite copies of Swastik graph

copies of Swastik graph Swn (k is odd ), Jelly fish Petersen graph are sum divisor cordial graphs. Sugumaran and Rajesh

Theta graph and some graph operations in Theta graph are sum divisor cordial graphs. Ganesan and Balamurugan  have discussed the prime labeling of Herschel

this paper is to prove the Herschel graph and some graph graph namely fusion, duplication, switching of a central vertex, path

graphs are sum divisor cordial graphs.

 Let G=( ( ), ( ))V G E G be a simple graph and let : ( ) {1, 2,...,| ( ) |}

f V G V G be a bijection. For each edge

### uv

, assign the label ( ) | ( )

f v f v and the label

### 0

otherwise. The function

if |ef(0)−ef(1) | ≤1. A graph which admits a divisor cordial divisor cordial graph.

 Let G=( ( ), ( ))V G E G be a simple graph and let : ( ) {1, 2,...,| ( ) |}

f V G V G be a bijection. For each edge

### uv

, assign the label 2 | ( ( ) ( )) and assign the label

### 0

otherwise. The function

isor cordial labeling if |ef(0)−ef(1) |≤1. A graph which admits a divisor cordial labeling is called a sum divisor cordial graph.

Herschel graph Hs is a bipartite undirected graph with 11 vertices

Figure 1: Herschel graph Hs

fix the position of vertices v u u, ,1 2,...,u10 of Hs 1, unless or otherwise specified.

and

### v

be two distinct vertices of a graph

### G

. A new graph

(identifying) two vertices

and

### v

by a single vertex

 . Lourdusamy . Sugumaran and , path union of finite copies of Swastik graph

y fish J n n( , ) and  proved that the Theta graph and some graph operations in Theta graph are sum divisor cordial graphs. rime labeling of Herschel graph. Our graph and some graph operations graph namely fusion, duplication, switching of a central vertex, path union of

be a simple graph and let , assign the label 1 if The function f is called a . A graph which admits a divisor cordial

be a simple graph and let , assign the label 1 if The function f is called a . A graph which admits a sum

ed graph with 11 vertices

s

H as indicated in

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467

such that every edge which was incident with either

(or)

in

### G

now incident with

### x

in G1.

Definition 1.5. Duplication of a vertex vk of a graph

### G

produces a new graph G1 by adding a vertex vk′ with N v( )k =N v( )k′ . In other words, a vertex vk′ is said to be a

duplication of vk if all the vertices which are adjacent to vk are now adjacent to vk′.

Definition 1.6. A vertex switching Gv of a graph

### G

is obtained by taking a vertex

of

### G

, removing the entire edges incident with

### v

and adding edges joining

### v

to every vertex which are non-adjacent to

in

### G

.

Definition 1.7.  Let

### G

be a graph and let G1=G2 = = Gn =G, where

### 2

. Then the graph obtained by adding an edge from each Gi to Gi+1 (1≤ ≤ −i n 1) is called

the path union of

### G

.

2. Main results

Theorem 2.1. The Herschel graph Hs is a sum divisor cordial graph. Proof: Let G=Hs be a Herschel graph and let v be the central vertex and

(1 10)

i

u ≤ ≤i be the remaining vertices of the Herschel graph. Then | ( ) |V G = 11 and |E G( ) | = 18. We define the vertex labeling f V G: ( )→{1, 2,...,| ( ) |}V G as follows.

( ) 11

f v = , f u( 2) 1= , f u( )8 =4,

( )i

f u =i; i=3, 9,10, ( )i 1

f u = +i ; i=1, 4, 5, 6, 7.

From the above labeling pattern, we have ef(0)=ef(1)=9.

Hence |ef(0)−ef(1) | ≤1.

Thus

### G

is a sum divisor cordial graph.

Example 2.1. The sum divisor cordial labeling of Herschel graph Hs is shown in Figure 2.

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Theorem 2.2. The fusion of any two adjacent vertices of degree 3 in the Herschel graph is a sum divisor cordial graph.

Proof: Let Hs be the Herschel graph with | (V Hs) |= 11 and | (E Hs) |= 18. Let v be the central vertex of the Herschel graph and it has 3 vertices of degree 4 and 8 vertices of degree 3. Let G be the graph obtained by fusion of two adjacent vertices of degree 3 in the Herschel graph of Hs. Then | ( ) |V G = 10 and |E G = 17. ( ) |

We define the vertex labeling f V G: ( )→{1, 2,...,| ( ) |}V G as follows. Case 1. Fusion of u6 and u10.

Suppose that u6 and u10are fused together as a single vertex u. ( ) 1

f v = ,

3

( ) 7

f u = ,

( ) 4

f u = ,

( )i 1

f u = +i ; i=1, 2, 4, 5, 7,8,9.

Case 2. Fusion of u6 and u2.

Suppose that u6 and u2are fused together as a single vertex u. ( ) 1

f v = , f u( 4)=7, f u( 10)=4, ( ) 2

f u = ,

( )i 1

f u = +i ; i=5, 7,8, 9.

( )i 2

f u = +i ; i=1, 3.

Case 3. Fusion of u6 and u3.

Suppose that u6 and u3are fused together as a single vertex u. ( ) 1

f v = , f u( )1 =9, f u( 10)=4, ( ) 2

f u = ,

( )i

f u =i; i=7,8. ( )i 1

f u = +i ; i=2, 4, 5, 9.

Case 4. Fusion of u5 and u9.

Suppose that u5 and u9are fused together as a single vertex u.

( ) 1

f v = , f u( )3 =7, ( ) 4

f u = ,

( )i

f u =i; i=6,10. ( )i 1

f u = +i ; i=1, 2, 4, 7,8.

Case 5. Fusion of u5 and u4.

Suppose that u5 and u4are fused together as a single vertex u. ( ) 1

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469 ( ) 4

f u = ,

( )i

f u =i; i=6,10. ( )i 1

f u = +i ; i=1, 2, 7,8.

Case 6. Fusion of u5 and u1.

Suppose that u5 and u1are fused together as a single vertex u. ( ) 1

f v = , f u( )3 =7, f u( )9 =4,

( ) 2

f u = ,

( )i

f u =i; i=6,10. ( )i 1

f u = +i ; i=2, 4, 7,8.

From all the above cases, we have|ef(0)−ef(1) |≤1.

Thus

### G

is a sum divisor cordial graph.

Example 2.2. The sum divisor cordial labeling of fusion of u6 and

10

u in

s

H is shown in Figure 3.

Figure 3: Sum divisor cordial labeling of fusion of u6 and

10

u in

s

H .

Theorem 2.3. The duplication of any vertex of degree 3 in a Herschel graph is a sum divisor cordial graph.

Proof: Let Hs be the Herschel graph with | (V Hs) |= 11 and | (E Hs) |= 18. Let v be the central vertex and uk′ be the duplication of the vertex uk in the Herschel graph Hs. Let

### G

be the graph obtained by duplicating the vertex uk of degree 3 in Hs. Then | ( ) |V G = 12 and |E G( ) | = 21.

Case 1. Duplication of vertex uk, where k=1, 2, 3, 4, 5, 6,10. We define the vertex labeling f V G: ( )→{1, 2,...,| ( ) |}V G as follows.

( ) 1

f v = , f u( )3 =11, f u( )8 =4, f u( k′ =) 12, ( )i

f u =i; i=9,10.

( )i 1

f u = +i ; i=1, 2, 4, 5, 6, 7.

Case 2. Duplication of vertex u9.

( ) 9

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( )i

f u =i; i=1, 2,3,5, 6. ( )i 1

f u = +i ; i=7,9,10.

From the above two cases, we have |ef(0)−ef(1) | ≤1.

Thus

### G

is a sum divisor cordial graph.

Example 2.3. The sum divisor cordial labeling of the duplication of the vertex u10 in Hs is shown in Figure 4.

Figure 4: Sum divisor cordial labeling of the duplication of the vertex u10

Theorem 2.4. The switching of a central vertex v in the Herschel graph Hs is a sum divisor cordial graph.

Proof: Let Hs be the Herschel graph with | (V Hs) |= 11 and | (E Hs) |= 18. Let v be the central vertex and G be the new graph obtained by switching the central vertex v. Then| ( ) |V G = 11 and | ( ) |E G = 20.

We define the vertex labeling f V G: ( )→{1, 2,...,| ( ) |}V G as follows. ( ) 1

f v = ,

3

( ) 11

f u = ,

8

( ) 6

f u = ,

( )i

f u =i; i=4, 5, 9,10. ( )i 1

f u = +i ; i=1, 2, 6, 7.

From the above labeling pattern, we observe that ef(0)=ef(1)=10.

Hence |ef(0)−ef(1) | ≤1.

Thus

### G

is a sum divisor cordial graph.

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471

Figure 5: Sum divisor cordial labeling of switching of a central vertex v in Hs.

Theorem 2.5. The graph obtained by path union of two copies of Herschel graphs Hs is a sum divisor cordial graph.

Proof: Consider two copies of Herschel graphs H1s and

2

s

H respectively. Let

1

( s) { , i:1 10}

V H = u u ≤ ≤i and let V H( s2)={ ,v vi:1≤ ≤i 10}. Then

1

| (V Hs) |= 11 and

1

| (E Hs) |= 18 and | (V Hs2) |= 11 and | (E Hs2) |= 18. Let

### G

be the graph obtained by

the path union of two copies of Herschel graphs H1s and

2

s H . Then

1 2

( ) ( s) ( s)

V G =V HV H and E G( )=E H( s1)∪E H( s2)∪{u v8 8}. Note that

### G

has 22

vertices and 37 edges.

We define the vertex labeling f V G: ( )→{1, 2,...,| ( ) |}V G as follows. Labeling of H1s:

( ) 1

f u = , f u( )3 =9, f u( )5 =11, f u( )8 =6, f u( )9 =4, f u( 10)=10,

( )i 1

f u = +i ; i=1, 2, 4, 6, 7.

Labeling of Hs2: ( ) 12

f v = ,

3

( ) 19

f v = ,

5

( ) 15

f v = ,

7

( ) 20

f v = ,

8

( ) 17

f v = ,

9

( ) 22

f v = , f v( 10)=21,

( )i 12

f v = +i ; i=1, 2, 4, 6.

From the above labeling pattern, we observe that ef(0)=18 and ef(1)=19.

Hence |ef(0)−ef(1) | ≤1.

Thus

### G

is a sum divisor cordial graph.

Example 2.5. The sum divisor cordial graph of the path union of H1s and

2

s

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Figure 6: The sum divisor cordial graph of the path union of

3. Conclusion

In this paper, we have investigated Herschel graph and proved

degree 3 in Hs, duplication of any inHsand path union of two copies of

Acknowledgement. The authors are grateful to the anonymous referee for providing valuable comments and suggestions to improve this paper from its earlier version.

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The sum divisor cordial graph of the path union of H1s

investigated the sum divisor cordiality on special graph namely graph and proved that the Herschel graphHs, fusion of any two vertices of uplication of any vertex of degree 3 inHs, switching of central vertex

of two copies of Hs are sum divisor cordial graphs.

The authors are grateful to the anonymous referee for providing uable comments and suggestions to improve this paper from its earlier version.

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## Figure Figure 2: Sum divisor cordial labeling of Herschel graph H s p.3 Figure 3: Sum divisor cordial labeling of fusion of u and 6u10 in H . s p.5 Figure 4: Sum divisor cordial labeling of the duplication of the vertex u10 p.6 Figure 5: Sum divisor cordial labeling of switching of a central vertex v in H .s p.7 Figure 6: The sum divisor cordial graph of the path union ofThe sum divisor cordial graph of the path union of H 1s1s and H .2s p.8

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