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Kragujevac Journal of Mathematics Volume 37(1) (2013), Pages 163–186. F -GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND THORN GRAPHS A. DURAI BASKAR, S. AROCKIARAJ AND B. RAJENDRAN Abstract. A function f is called a F -Geometric mean labeling of a graph G(V,E) if f : V (G) →{1, 2, 3,...,q +1} is injective and the induced function f * : E(G) {1, 2, 3,...,q} defined as f * (uv)= f (u)f (v) , for all uv E(G), is bijective. A graph that admits a F -Geometric mean labelling is called a F -Geometric mean graph. In this paper, we have discussed the F -Geometric mean labeling of some chain graphs and thorn graphs. 1. Introduction Throughout this paper, by a graph we mean a finite, undirected and simple graph. Let G(V,E) be a graph with p vertices and q edges. For notations and terminology, we follow [3]. For a detailed survey on graph labeling, we refer [2]. Path on n vertices is denoted by P n and a cycle on n vertices is denoted by C n . G K 1 is the graph obtained from G by attaching a new pendant vertex to each vertex of G. A star graph S m is the complete bipartite graph K 1,m .G S 2 is the graph obtained from G by attaching two pendant vertices at each vertex of G. If v (i) 1 ,v (i) 2 ,v (i) 3 ,...,v (i) m+1 and u 1 ,u 2 ,u 3 ...,u n be the vertex of the star graph S m and the path P n , then the graph (P n ; S m ) is obtained from n copies of S m and the path P n by joining u i with the central vertex v (i) 1 of the i th copy of S m by means of an edge, for 1 i n. The H graph is obtained from two paths u 1 ,u 2 ,...,u n and v 1 ,v 2 ,...,v n of equal length by joining an edge u n+1 2 v n+1 2 when n is odd and u n+2 2 v n 2 when n is even. Let G 1 and G 2 be any two graphs with p 1 and p 2 vertices, respectively. Then the cartesian product G 1 × G 2 has p 1 p 2 vertices which are {(u, v)/u G 1 ,v G 2 }. The edges are defined as follows: (u 1 ,v 1 ) and (u 2 ,v 2 ) are adjacent in G 1 × G 2 if either Key words and phrases. Labeling, F -Geometric mean labeling, F -Geometric mean graph. 2010 Mathematics Subject Classification. 05C78. Received: February 18, 2012. Revised: January 29, 2013. 163

F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

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Page 1: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

Kragujevac Journal of Mathematics

Volume 37(1) (2013), Pages 163–186.

F -GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHSAND THORN GRAPHS

A. DURAI BASKAR, S. AROCKIARAJ AND B. RAJENDRAN

Abstract. A function f is called a F -Geometric mean labeling of a graph G(V,E)if f : V (G) → {1, 2, 3, . . . , q + 1} is injective and the induced function f∗ : E(G) →{1, 2, 3, . . . , q} defined as f∗(uv) =

⌊√f(u)f(v)

⌋, for all uv ∈ E(G), is bijective.

A graph that admits a F -Geometric mean labelling is called a F -Geometric meangraph. In this paper, we have discussed the F -Geometric mean labeling of somechain graphs and thorn graphs.

1. Introduction

Throughout this paper, by a graph we mean a finite, undirected and simple graph.Let G(V,E) be a graph with p vertices and q edges. For notations and terminology,we follow [3]. For a detailed survey on graph labeling, we refer [2].

Path on n vertices is denoted by Pn and a cycle on n vertices is denoted by Cn.G ⊙ K1 is the graph obtained from G by attaching a new pendant vertex to eachvertex of G. A star graph Sm is the complete bipartite graph K1,m. G ⊙ S2 is thegraph obtained from G by attaching two pendant vertices at each vertex of G. If

v(i)1 , v

(i)2 , v

(i)3 , . . . , v

(i)m+1 and u1, u2, u3 . . . , un be the vertex of the star graph Sm and the

path Pn, then the graph (Pn;Sm) is obtained from n copies of Sm and the path Pn by

joining ui with the central vertex v(i)1 of the ith copy of Sm by means of an edge, for

1 ≤ i ≤ n. The H− graph is obtained from two paths u1, u2, . . . , un and v1, v2, . . . , vnof equal length by joining an edge un+1

2

vn+1

2

when n is odd and un+2

2

vn2when n is

even. Let G1 and G2 be any two graphs with p1 and p2 vertices, respectively. Thenthe cartesian product G1 × G2 has p1p2 vertices which are {(u, v)/u ∈ G1, v ∈ G2}.The edges are defined as follows: (u1, v1) and (u2, v2) are adjacent in G1×G2 if either

Key words and phrases. Labeling, F -Geometric mean labeling, F -Geometric mean graph.2010 Mathematics Subject Classification. 05C78.Received: February 18, 2012.Revised: January 29, 2013.

163

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164 A. DURAI BASKAR, S. AROCKIARAJ AND B. RAJENDRAN

u1 = u2 and v1 and v2 are adjacent in G2 or u1 and u2 are adjacent in G1 and v1 = v2.The Ladder graph Ln is obtained from Pn × P2.

The study of graceful graphs and graceful labeling methods first introduced by Rosa[5]. The concept of mean labeling was first introduced by S. Somasundaram and R.Ponraj [6] and it was developed in [4] and [7]. In [10], R. Vasuki et al. discussedthe mean labeling of cyclic snake and armed crown. In [8], S. Somasundaram et al.defined the geometric mean labeling as follows.

A graphG = (V,E) with p vertices and q edges is said to be a geometric mean graphif it is possible to label the vertices x ∈ V with distinct labels f(x) from 1, 2, . . . , q+1

in such way that when each edge e = uv is labeled with f(uv) =⌊√

f(u)f(v)⌋or

⌈√f(u)f(v)

⌋then the edge labels are distinct.

In the above definition, the readers will get some confusion in finding the edgelabels which edge is assigned by flooring function and which edge is assigned byceiling function.

In [9], they have given the geometric mean labeling of the graph C5 ∪C7 as in theFigure 1.

qq

q

q

q

q q q

qq

q q

1

1

2

3

3 4 4

5

5

2 6 6 7

7

8

9

910101111

12

12

8 u

v

w

Figure 1. A Geometric mean labeling of C5 ∪ C7.

From the above figure, for the edge uv, they have used flooring function⌊√

f(u)f(v)⌋

and for the edge vw, they have used ceiling function⌈√

f(u)f(v)⌉for fulfilling their

requirement. To avoid the confusion of assigning the edge labels in their definition,

we just consider the flooring function⌊√

f(u)f(v)⌋for our discussion. Based on

our definition, the F -Geometric mean labeling of the same graph C5 ∪ C7 is given inFigure 2.

q

q q

q q

q

q q

q q

q q

12

7

5

5

4

4

3

3

16

79

9

11

11

13

12

12

10

10

8

86

Figure 2. A F -Geometric mean labeling of C5 ∪ C7

In [1], A. Durai Baskar et al. introduced Geometric mean graph.A function f is called a F -Geometric mean labeling of a graph G(V,E) if

f : V (G) → {1, 2, 3, . . . , q + 1} is injective and the induced function f ∗ : E(G) →

Page 3: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

F -GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND THORN GRAPHS 165

{1, 2, 3, . . . , q} defined as

f ∗(uv) =⌊√

f(u)f(v)⌋, for all uv ∈ E(G),

is bijective. A graph that admits a F -Geometric mean labeling is called a F -Geometricmean graph.

The graph shown in Figure 3 is a F -Geometric mean graph.

rr

r r r

rrr

r r

rr

1

1

2

2

33571010111112

12

14

15

17

14

16

4

516

139

9 8 8

6

Figure 3. A F -Geometric mean graph

In this paper, we have discussed the F -Geometric mean labeling of some chaingraphs and thorn graphs.

2. Main Results

The graph G∗(p1, p2, . . . , pn) is obtained from n cycles of length p1, p2, . . . , pn byidentifying consecutive cycles at a vertex as follows. If the jth cycle is of odd length,

then its(

pj+3

2

)th

vertex is identified with the first vertex of (j + 1)th cycle and if the

jth cycle is of even length, then its(

pj+2

2

)th

vertex is identified with the first vertex

of (j + 1)th cycle.

Theorem 2.1. G∗(p1, p2, . . . , pn) is a F -Geometric mean graph for any pj, for

1 ≤ j ≤ n.

Proof. Let {v(j)i ; 1 ≤ j ≤ n, 1 ≤ i ≤ pj} be the vertices of the n number of cycles.

For 1 ≤ j ≤ n− 1, the jth and (j + 1)th cycles are identified by a vertex v(j)pj+3

2

and

v(j+1)1 while pj is odd and v

(j)pj+2

2

and v(j+1)1 while pj is even.

We define f : V [G∗(p1, p2, . . . , pn] →{1, 2, 3, . . . ,

n∑j=1

pj + 1

}as follows:

f(v(1)i ) =

{2i− 1 1 ≤ i ≤

⌊p12

⌋+ 1

2p1 − 2(i− 2)⌊p12

⌋+ 2 ≤ i ≤ p1

and

Page 4: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

166 A. DURAI BASKAR, S. AROCKIARAJ AND B. RAJENDRAN

for 2 ≤ j ≤ n,

f(v(j)i ) =

j−1∑k=1

pk + 2i− 1 2 ≤ i ≤⌊pj

2

⌋+ 1

j−1∑k=1

pk + 2(i− 1) i =⌊pj

2

⌋+ 2 and pj is odd

j−1∑k=1

pk + 2(i− 2) i =⌊pj

2

⌋+ 2 and pj is even

j−1∑k=1

pk + 2pj − 2(i− 2) i =⌊pj

2

⌋+ 3 ≤ i ≤ pj

The induced edge labeling is as follows:

f ∗(v(1)i v

(1)i+1) =

2i− 1 1 ≤ i ≤⌊p12

2i− 1 i =⌊p12

⌋+ 1 and p1 is odd

2p1 − 2(i− 1) i =⌊p12

⌋+ 1 and p1 is even

2p1 − 2(i− 1)⌊p12

⌋+ 2 ≤ i ≤ p1 − 1,

f ∗(v(1)p1v(1)1 ) = 2,

for 2 ≤ j ≤ n,

f ∗(v(j)i v

(j)i+1) =

j−1∑k=1

pk + 2i− 1 1 ≤ i ≤⌊pj

2

j−1∑k=1

pk + 2i− 1 i =⌊pj

2

⌋+ 1 and pj is odd

j−1∑k=1

pk + 2pj − 2(i− 1) i =⌊pj

2

⌋+ 1 and pj is even

j−1∑k=1

pk + 2pj − 2(i− 1)⌊pj

2

⌋+ 2 ≤ i ≤ pj − 1

and

f ∗(v(j)pjv(j)1 ) =

j−1∑

k=1

pk + 2.

Hence, f is a F -Geometric mean labeling of G∗(p1, p2, . . . , pn). Thus the graphG∗(p1, p2, . . . , pn) is a F -Geometric mean graph. �

A F -Geometric mean labeling of G∗(10, 9, 12, 4, 5) is as shown in Figure 4.

Page 5: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

F -GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND THORN GRAPHS 167

q

q

qq

q

qq

q

q

q

q

q

q

q

q

q

q

q

q

q

q

qq

qq

q q

q q

q

q

q

q

q

q

q

11

9

9775

5

3311

24

4

6 6

8

8 10

10

11

1213

15 15

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17 19

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20

18

1816

16

1414

12

20

22 22

24242626 28

28 30

30

3231

3129

2927

27

2525

2323

21

32

34

34

36

35

35

33

36

38 38

40

40

41

39

39

37

Figure 4. A F -Geometric mean labeling of G∗(10, 9, 12, 4, 5)

The graph G′(p1, p2, . . . , pn) is obtained from n cycles of length p1, p2, . . . , pn by iden-

tifying consecutive cycles at an edge as follows: The(

pj+3

2

)th

edge of jth cycle is

identified with the first edge of (j + 1)th cycle when j is odd and the(

pj+1

2

)th

edge

of jth cycle is identified with the first edge of (j + 1)th cycle when j is even.

Theorem 2.2. G′(p1, p2, . . . , pn) is a F -Geometric mean graph if all pj’s are odd or

all pj’s are even, for 1 ≤ j ≤ n.

Proof. Let {v(j)i ; 1 ≤ j ≤ n, 1 ≤ i ≤ pj} be the vertices of the n number of cycles.

Case (i) pj is odd, for 1 ≤ j ≤ n.For 1 ≤ j ≤ n − 1, the jth and (j + 1)th cycles are identified by the edges

v(j)pj+1

2

v(j)pj+3

2

and v(j+1)1 v

(j+1)pj+1 while j is odd and v

(j)pj−1

2

v(j)pj+1

2

and v(j+1)1 v

(j+1)pj+1 while j is

even.

We define f : V [G′(p1, p2, . . . , pn)] →{1, 2, 3, . . . ,

n∑j=1

pj − n + 2

}as follows:

f(v(1)i ) =

1 i = 12i 2 ≤ i ≤

⌊p12

⌋+ 1

2p1 + 3− 2i⌊p12

⌋+ 2 ≤ i ≤ p1

and for 2 ≤ j ≤ n,

f(v(j)i ) =

j−1∑k=1

pk − j + 2i+ 2 2 ≤ i ≤⌊pj

2

⌋and j is even

j−1∑k=1

pk + 2pj + 3− j − 2i⌊pj

2

⌋+ 1 ≤ i ≤ pj − 1 and j even

j−1∑k=1

pk − j + 2i+ 1 2 ≤ i ≤⌊pj

2

⌋+ 1 and j is odd

j−1∑k=1

pk + 2pj + 4− j − 2i⌊pj

2

⌋+ 2 ≤ i ≤ pj − 1 and j odd.

Page 6: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

168 A. DURAI BASKAR, S. AROCKIARAJ AND B. RAJENDRAN

The induced edge labeling is as follows:

f ∗(v(1)i v

(1)i+1) =

{2i 1 ≤ i ≤

⌊p12

2p1 + 1− 2i⌊p12

⌋+ 1 ≤ i ≤ p1 − 1,

f ∗(v(1)p1v(1)1 ) = 1

and for 2 ≤ j ≤ n,

f ∗(v(j)i v

(j)i+1) =

j−1∑k=1

pk − j + 2i+ 2 1 ≤ i ≤⌊pj

2

⌋and j is even

j−1∑k=1

pk + 2pj + 1− j − 2i⌊pj

2

⌋+ 1 ≤ i ≤ pj − 1 and j even

j−1∑k=1

pk − j + 2i+ 1 1 ≤ i ≤⌊pj

2

⌋and j is odd

j−1∑k=1

pk + 2pj + 2− j − 2i⌊pj

2

⌋+ 1 ≤ i ≤ pj − 1 and j odd.

Case (ii) pj is even, for 1 ≤ j ≤ n.For 1 ≤ j ≤ n − 1, the jth and (j + 1)th cycles are identified by the edges

v(j)pj

2

v(j)pj+2

2

and v(j+1)1 v

(j+1)pj+1

.

We define f : V [G′(p1, p2, . . . , pn)] →{1, 2, 3, . . . ,

n∑j=1

pj − n+ 2

}as follows:

f(v(1)i ) =

1 i = 12i 2 ≤ i ≤

⌊p12

2p1 + 3− 2i⌊p12

⌋+ 1 ≤ i ≤ p1

and for 2 ≤ j ≤ n,

f(v(j)i ) =

j−1∑k=1

pk − j + 2i+ 1 2 ≤ i ≤⌊pj

2

j−1∑k=1

pk + 2pj + 4− j − 2i⌊pj

2

⌋+ 1 ≤ i ≤ pj − 1.

The induced edge labeling is as follows:

f ∗(v(1)i v

(1)i+1) =

{2i 1 ≤ i ≤

⌊p12

2p1 + 1− 2i⌊p12

⌋+ 1 ≤ i ≤ p1 − 1,

f ∗(v(1)p1v(1)1 ) = 1

Page 7: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

F -GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND THORN GRAPHS 169

and for 2 ≤ j ≤ n,

f ∗(v(j)i v

(j)i+1) =

j−1∑k=1

pj − j + 2i+ 1 1 ≤ i ≤⌊pj

2

j−1∑k=1

pk + 2pj + 2− j − 2i⌊pj

2

⌋+ 1 ≤ i ≤ pj − 1.

Hence, f is a F -Geometric mean labeling of G′(p1, p2, . . . , pn). Thus the graphG′(p1, p2, . . . , pn) is a F -Geometric mean graph. �

A F -Geometric mean labeling of G′(7, 5, 9, 13) and G′(4, 8, 10, 6) is as shown inFigure 5.

q

q

q

q

q

q

q

q

q

q

q

q

q

q

q

q

q

qq

q

q

q

q

q

q

q

q

5

8

77

6

644

2

11

3 35 8

10

10

1211

11

9

13

14 14

16

16

20

q18

18

19

17

17

1515

12

21

23 23

2525

27

27 29

29

31

31

32303028

282626

2424

2222

1920

q

q

q

q

q

q

q

q

q

q

q

q

qq

q

q

qq q

q q q

1

1

3 3

54

4

2

5

7 7 9

9

111112

10

1088

6

12

14 14

16

16 18

1820

2021

19

1917

17

1515

13

21

23

23

25

25

2624

24

22

Figure 5. F -Geometric mean labeling of G′(7, 5, 9, 13) and G′(4, 8, 10, 6)

The graph G(p1, m1, p2, m2, . . . , mn−1, pn) is obtained from n cycles of lengthp1, p2, . . . , pn and (n − 1) paths on m1, m2, . . . , mn−1 vertices respectively by iden-tifying a cycle and a path at a vertex alternatively as follows: If the jth cycles is of

odd length, then its(

pj+3

2

)th

vertex is identified with a pendant vertex of jth path

and if the jth cycle is of even length, then its(

pj+2

2

)th

vertex is identified with a

pendant vertex of jth path while the other pendant vertex of the jth path is identifiedwith the first vertex of the (j + 1)th cycle.

Theorem 2.3. G(p1, m1, p2, m2, . . . , mn−1pn) is a F -Geometric mean graph for any

pj’s and mj’s.

Proof. Let {v(j)i ; 1 ≤ j ≤ n, 1 ≤ i ≤ pj} and {u(j)i ; 1 ≤ j ≤ n− 1, 1 ≤ i ≤ mj} be the

n number of cycles and (n− 1) number of paths respectively.

Page 8: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

170 A. DURAI BASKAR, S. AROCKIARAJ AND B. RAJENDRAN

For 1 ≤ j ≤ n − 1, the jth cycle and jth path are identified by a vertex v(j)pj+2

2

and

u(j)1 while pj is even and v

(j)pj+3

2

and u(j)1 while pj is odd. And the jth path and (j+1)th

cycle are identified by a vertex u(j)mj and v

(j+1)1 .

We define f : V [G(p1, m1, p2, m2, . . . , mn−1, pn)] →{1, 2, 3, . . . ,

n−1∑j=1

(pj +mj)+ pn −

n+ 2}as follows:

f(v(1)i ) =

{2i− 1 1 ≤ i ≤

⌊p12

⌋+ 1

2p1 + 4− 2i⌊p12

⌋+ 2 ≤ i ≤ p1,

f(u(1)i ) = p1 + i, for 2 ≤ i ≤ m1,

for 2 ≤ j ≤ n,

f(v(j)i ) =

j−1∑k=1

(pk +mk) + 2i− j 2 ≤ i ≤⌊pj

2

⌋+ 1

j−1∑k=1

(pk +mk) + 2i− j − 1 i =⌊pj

2

⌋+ 2

and pj is odd

j−1∑k=1

(pk +mk) + 2i− j − 3 i =⌊pj

2

⌋+ 2 and

pj is even

j−1∑k=1

(pk +mk) + 2pj − 2i− j + 5⌊pj

2

⌋+ 3 ≤ i ≤ pj

and for 3 ≤ j ≤ n,

f(u(j−1)i ) =

j−2∑

k=1

(pk +mk) + pj−1 + i+ 2− j, for 2 ≤ i ≤ mj−1

The induced edge labeling is as follows:

f ∗(v(1)i v

(1)i+1) =

2i− 1 1 ≤ i ≤⌊p12

2i− 1 i =⌊p12

⌋+ 1 and

p1 is odd2p1 − 2i+ 2 i =

⌊p12

⌋+ 1 and

p1 is even2p1 − 2i+ 2

⌊p12

⌋+ 2 ≤ i ≤ p1 − 1,

f ∗(v(1)p1v(1)1 ) = 2,

f ∗(u(1)i u

(1)i+1) = p1 + i, for 1 ≤ i ≤ m1 − 1,

Page 9: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

F -GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND THORN GRAPHS 171

for 2 ≤ j ≤ n,

f ∗(v(j)i v

(j)i+1) =

j−1∑k=1

(pk +mk) + 2i− j 1 ≤ i ≤⌊pj

2

j−1∑k=1

(pk +mk) + 2i− j i =⌊pj

2

⌋+ 1 and

pj is odd

j−1∑k=1

(pk +mk) + 2pj − 2i− j + 3 i =⌊pj

2

⌋+ 1 and

pj is even

j−1∑k=1

(pk +mk) + 2pj − 2i− j + 3⌊pj

2

⌋+ 2 ≤ i ≤ pj − 1,

f ∗(v(j)pjv(j)1 ) =

j−1∑

k=1

(pk +mk)− j + 3

and for 3 ≤ j ≤ n,

f ∗(u(j−1)i u

(j−1)i+1 ) =

j−2∑

k=1

(pk +mk) + pj−1 + i+ 2− j, for 1 ≤ i ≤ mj−1 − 1.

Hence, f is a F -Geometric mean labeling of G(p1, m1, p2, m2 . . . , mn−1, pn). Thus the

graph G(p1, m1, p2, m2 . . . , mn−1, pn) is a F -Geometric mean graph. �

A F -Geometric mean labeling of G(8, 4, 5, 6, 10) is as shown in Figure 6.

rr

r

r

r

rr

r

rr r r

r

r

r

rr r r r r

r

r

r

rr

r

r

r

1

1

3 3

5

5 7

7

9

8

86

6

44

2

91010

1111

12

12

14 14

16

16

17

15

15

13

171818191920

202121 22

2224 24

26 26

28

2830

30

3231

3129

2927

27

2525

23

Figure 6. A F -Geometric mean labeling of G(8, 4, 5, 6, 10)

Theorem 2.4. Cn ⊙K1 is a F -Geometric mean graph, for n ≥ 3.

Proof. Let v1, v2, . . . , vn be the vertices of the cycle Cn and let ui be the pendantvertices attached at each vi, for 1 ≤ i ≤ n. Consider the graph Cn ⊙K1, for n ≥ 4.Case (i)

⌊√2n+ 1

⌋is odd.

Page 10: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

172 A. DURAI BASKAR, S. AROCKIARAJ AND B. RAJENDRAN

We define f : V [Cn ⊙K1] → {1, 2, 3, . . . , 2n+ 1} as follows:

f(vi) =

1 i = 1

2i 2 ≤ i ≤⌊√

2n+12

⌋+ 1

2i+ 1⌊√

2n+12

⌋+ 2 ≤ i ≤ n

and

f(ui) =

2 i = 1

2i− 1 2 ≤ i ≤⌊√

2n+12

2i+ 1 i =⌊√

2n+12

⌋+ 1

2i⌊√

2n+12

⌋+ 2 ≤ i ≤ n.

The induced edge labeling is as follows:

f ∗(vivi+1) =

2i 1 ≤ i ≤⌊√

2n+12

2i+ 1⌊√

2n+12

⌋+ 1 ≤ i ≤ n− 1,

f ∗(v1vn) =⌊√

2n+ 1⌋

and

f ∗(uivi) =

2i− 1 1 ≤ i ≤⌊√

2n+12

2i⌊√

2n+12

⌋+ 1 ≤ i ≤ n.

Case (ii)⌊√

2n+ 1⌋is even.

We define f : V [Cn ⊙K1] → {1, 2, 3, . . . , 2n+ 1} as follows:

f(vi) =

1 i = 1

2i 2 ≤ i ≤⌊√

2n+12

2i+ 1⌊√

2n+12

⌋+ 1 ≤ i ≤ i ≤ n

and

f(ui) =

2 i = 1

2i− 1 2 ≤ i ≤⌊√

2n+12

2i⌊√

2n+12

⌋+ 1 ≤ i ≤ n.

The induced edge labeling is as follows:

f ∗(vivi+1) =

2i 1 ≤ i ≤⌊√

2n+12

⌋− 1

2i+ 1⌊√

2n+12

⌋≤ i ≤ n− 1,

f ∗(v1vn) =⌊√

2n+ 1⌋

and

f ∗(uivi) =

2i− 1 1 ≤ i ≤⌊√

2n+12

2i⌊√

2n+12

⌋+ 1 ≤ i ≤ n.

Page 11: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

F -GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND THORN GRAPHS 173

Hence, the graph Cn ⊙K1, for n ≥ 4 admits F -Geometric mean labeling. �

For n = 3, a F -Geometric mean labeling of C3 ⊙K1 is as shown in Figure 7.r

r

r r rr

1

1

2

3

76

65445

2

Figure 7. A F - Geometric mean labeling of C3 ⊙K1

A F -Geometric mean labeling of C12 ⊙K1 is as shown in Figure 8.

r

r

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1212

1010

88

67

3

3

Figure 8. A F -Geometric mean labeling of C12 ⊙K1

Theorem 2.5. Cn ⊙ S2 is a F -Geometric mean graph for n ≥ 3.

Proof. Let u1, u2, . . . , un be the vertices of the cycle Cn. Let v(i)1 be the pendant

vertices at each vertex ui, for 1 ≤ i ≤ n. Therefore,

V [Cn ⊙ S2] = V (Cn) ∪ {v(i)1 , v(i)2 ; 1 ≤ i ≤ n}

andE[Cn ⊙ S2] = E(Cn) ∪ {uiv

(i)1 , uiv

(i)2 ; 1 ≤ i ≤ n}.

Page 12: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

174 A. DURAI BASKAR, S. AROCKIARAJ AND B. RAJENDRAN

Case (i)⌊√

6n⌋is a multiple of 3.

We define f : V [Cn ⊙ S2] → {1, 2, 3, . . . , 3n+ 1} as follows:

f(ui) =

3i− 1 1 ≤ i ≤⌊√

6n3

3i+ 1 i =⌊√

6n3

⌋+ 1

3i⌊√

6n3

⌋+ 2 ≤ i ≤ n,

f(v(i)1 ) =

3i− 2 1 ≤ i ≤⌊√

6n3

3i− 1⌊√

6n3

⌋+ 1 ≤ i ≤ n

and

f(v(i)2 ) =

3i 1 ≤ i ≤⌊√

6n3

⌋+ 1

3i+ 1⌊√

6n3

⌋+ 2 ≤ i ≤ n.

The induced edge labeling is as follows

f ∗(uiui+1) =

3i 1 ≤ i ≤⌊√

6n3

⌋− 1

3i+ 1⌊√

6n3

⌋≤ i ≤ n− 1,

f ∗(unu1) =⌊√

6n⌋,

f ∗(uiv(i)1 ) =

3i− 2 1 ≤ i ≤⌊√

6n3

3i− 1⌊√

6n3

⌋+ 1 ≤ i ≤ n

and

f ∗(uiv(i)2 ) =

3i− 1 1 ≤ i ≤⌊√

6n3

3i⌊√

6n3

⌋+ 1 ≤ i ≤ n.

Case (ii)⌊√

6n⌋is not a multiple of 3.

We define f : V [Cn ⊙ S2] → {1, 2, 3, . . . , 3n+ 1} as follows:

f(ui) =

3i− 1 1 ≤ i ≤⌊√

6n3

3i⌊√

6n3

⌋+ 1 ≤ i ≤ n,

f(v(i)1 ) =

3i− 2 1 ≤ i ≤⌊√

6n+13

3i− 1⌊√

6n+13

⌋+ 1 ≤ i ≤ n

Page 13: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

F -GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND THORN GRAPHS 175

and

f(v(i)2 ) =

3i 1 ≤ i ≤⌊√

6n3

3i+ 1⌊√

6n3

⌋+ 1 ≤ i ≤ n.

The induced edge labeling is as follows

f ∗(uiui+1) =

3i 1 ≤ i ≤⌊√

6n3

3i+ 1⌊√

6n3

⌋+ 1 ≤ i ≤ n− 1,

f ∗(unu1) =⌊√

6n⌋,

f ∗(uiv(i)1 ) =

3i− 2 1 ≤ i ≤⌊√

6n+13

3i− 1⌊√

6n+13

⌋+ 1 ≤ i ≤ n

and

f ∗(uiv(i)2 ) =

3i− 1 1 ≤ i ≤⌊√

6n3

3i⌊√

6n3

⌋+ 1 ≤ i ≤ n.

Hence, f is a F -Geometric mean labeling of Cn ⊙ S2. Thus the graph Cn ⊙ S2 is aF -Geometric mean graph, for n ≥ 3. �

A F -Geometric mean labeling of C6 ⊙ S2 is as shown in Figure 9.

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5 6

7

108 8

99

1012

1211

1113

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1516

1414

16

181717

18

196

Figure 9. A F -Geometric mean labeling of C6 ⊙ S2

Theorem 2.6. (Pn;Sm) is a F -Geometric mean graph, for m ≤ 2 and n ≥ 1.

Proof. Let u1, u2, . . . , un be the vertices of the path Pn and Let v(i)1 , v

(i)2 , . . . , v

(i)m+1

be the vertices of the star graph Sm such that v(i)1 is the central vertex of Sm, for

1 ≤ i ≤ n.

Page 14: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

176 A. DURAI BASKAR, S. AROCKIARAJ AND B. RAJENDRAN

Case (i) m = 1We define f : V [(Pn;Sm)] → {1, 2, 3, . . . , 3n} as follows:

f(ui) =

{3i 1 ≤ i ≤ n and i is odd3i− 2 1 ≤ i ≤ n and i is even,

f(v(i)1 ) = 3i− 1, for 1 ≤ i ≤ n

and

f(v(i)2 ) =

{3i− 2 1 ≤ i ≤ n and i is odd3i 1 ≤ i ≤ n and i is even.

The induced edge labeling is as follows

f ∗(uiui+1) = 3i, for 1 ≤ i ≤ n− 1,

f ∗(uiv(i)1 ) =

{3i− 1 1 ≤ i ≤ n and i is odd3i− 2 1 ≤ i ≤ n and i is even

and

f ∗(v(i)1 v

(i)2 ) =

{3i− 2 1 ≤ i ≤ n and i is odd3i− 1 1 ≤ i ≤ n and i is even.

Case (ii) m = 2We define f : V [(Pn;Sm)] → {1, 2, 3, . . . , 4n} as follows:

f(ui) =

{4i 1 ≤ i ≤ n and i is odd4i− 2 1 ≤ i ≤ n and i is even,

f(v(i)1 ) = 4i− 1, for 1 ≤ i ≤ n,

f(v(i)2 ) = 4i− 3, for 1 ≤ i ≤ n

and

f(v(i)3 ) =

{4i− 2 1 ≤ i ≤ n and i is odd4i 1 ≤ i ≤ n and i is even.

The induced edge labeling is as follows:

f ∗(uiui+1) = 4i, for 1 ≤ i ≤ n− 1,

f ∗(uiv(i)1 ) =

{4i− 1 1 ≤ i ≤ n and i is odd4i− 2 1 ≤ i ≤ n and i is even

f ∗(v(i)1 v

(i)2 ) = 4i− 3, for 1 ≤ i ≤ n

and

f ∗(v(i)1 v

(i)3 ) =

{4i− 2 1 ≤ i ≤ n and i is odd4i− 1 1 ≤ i ≤ n and i is even.

Hence, f is a F -Geometric mean labeling of (Pn;Sm.) Thus the graph (Pn;Sm) isa F -Geometric mean graph, for m ≤ 2 and n ≥ 1. �

A F -Geometric mean labeling of (P7;S1) and (P8;S2) is as shown in Figure 10.

Page 15: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

F -GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND THORN GRAPHS 177

s s s s s s s

s s s s s s s

s s s s s s s

3 3 4 6 9 9 10 12 15 15 16 18 21

20

20

19

191 6 7 12 13 18

1 5 7 11 13 172 5 8 11 14 17

2 4 8 10 14 16

s s s s s s s

s s s s s s s s

s

sss

ssssssssssss

s

4 4 6 8 12 12 14 16 20 20 22 24 28 28 30

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3229

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11

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8

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7

6

5

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2

2

3

3

1

1

Figure 10. A F -Geometric mean labeling of (P7;S1) and (P8;S2)

Theorem 2.7. For a H−graph G, G⊙K1 is a F -Geometric mean graph.

Proof. Let u1, u2, . . . , un and v1, v2, . . . , vn be the vertices of G. Therefore

V (G⊙K1) = V (G) ∪ {u′i, v

′i; 1 ≤ i ≤ n}

and

E(G⊙K1) = E(G) ∪ {uiu′i, viv

′i; 1 ≤ i ≤ n}.

Case (i) n ≡ 0(mod 4).We define f : V (G⊙K1) → {1, 2, 3, . . . , 4n} as follows:

f(ui) =

{2i− 1 1 ≤ i ≤ n and i is odd2i 1 ≤ i ≤ n and i is even,

f(u′i) =

{2i 1 ≤ i ≤ n and i is odd2i− 1 1 ≤ i ≤ n and i is even,

f(vi) =

{2n− 3 + 4i 1 ≤ i ≤

⌊n2

⌋− 1 and i is odd

2n− 1 + 4i 1 ≤ i ≤⌊n2

⌋and i is even,

f(vn+1−i) =

{2n− 2 + 4i 1 ≤ i ≤

⌊n2

⌋− 1 and i is odd

2n+ 4i 1 ≤ i ≤⌊n2

⌋and i is even,

Page 16: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

178 A. DURAI BASKAR, S. AROCKIARAJ AND B. RAJENDRAN

and

f(v′i) =

f(vi) + 2 1 ≤ i ≤⌊n2

⌋− 1 and i is odd

f(vi)− 2⌊n2

⌋+ 1 ≤ i ≤ n and i is odd

f(vi)− 2 1 ≤ i ≤⌊n2

⌋and i is even

f(vi) + 2⌊n2

⌋+ 2 ≤ i ≤ n and i is even.

The induced edge labeling is as follows:

f ∗(uiui+1) = 2i, for 1 ≤ i ≤ n− 1,

f ∗(uiu′i) = 2i− 1, for 1 ≤ i ≤ n,

f ∗(vivi+1) = 2n− 1 + 4i, for 1 ≤ i ≤⌊n2

⌋,

f ∗(vn+1−ivn−i) = 2n+ 4i, for 1 ≤ i ≤⌊n2

⌋− 1,

f ∗(viv′i) =

f(vi) 1 ≤ i ≤⌊n2

⌋− 1 and i is odd

f(vi)− 2⌊n2

⌋+ 1 ≤ i ≤ n and i is odd

f(vi)− 2 1 ≤ i ≤⌊n2

⌋and i is even

f(vi)⌊n2

⌋+ 2 ≤ i ≤ n and i is even

and

f ∗(ui+1vi) = 2n, for i =⌊n2

⌋.

Case (ii) n ≡ 1(mod 4).We define f : V (G⊙K1) → {1, 2, 3, . . . , 4n} as follows:

f(ui) = 2i, for 1 ≤ i ≤ n, f(u′i) = 2i− 1, for 1 ≤ i ≤ n,

f(vi) =

{2n− 3 + 4i 1 ≤ i ≤

⌊n2

⌋+ 1 and i is odd

2n− 1 + 4i 1 ≤ i ≤⌊n2

⌋and i is even,

f(vn+1 − i) =

{2n− 2 + 4i 1 ≤ i ≤

⌊n2

⌋and i is odd

2n + 4i 1 ≤ i ≤⌊n2

⌋and i is even

and

f(v′i) =

f(vi) + 2 1 ≤ i ≤⌊n2

⌋and i is odd

f(vi) + 1 i =⌊n2

⌋+ 1 and i is odd

f(vi) + 2⌊n2

⌋+ 3 ≤ i ≤ n and i is odd

f(vi)− 2 1 ≤ i ≤ n and i is even.

The induced edge labeling is as follows:

f ∗(uiui+1) = 2i, for 1 ≤ i ≤ n− 1,

f ∗(uiu′i) = 2i− 1, for 1 ≤ i ≤ n,

f ∗(vivi+1) = 2n− 1 + 4i, for 1 ≤ i ≤⌊n2

⌋,

f ∗(vn+1−ivn−i) = 2n+ 4i, for 1 ≤ i ≤⌊n2

⌋,

Page 17: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

F -GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND THORN GRAPHS 179

f ∗(viv′i) =

{f(vi) 1 ≤ i ≤ n and i is oddf(vi)− 2 1 ≤ i ≤ n and i is even

and

f ∗(uivi) = 2n, for i =⌊n2

⌋+ 1.

Case (iii) n ≡ 2(mod 4).We define f : V (G⊙K1) → {1, 2, 3, . . . , 4n} as follows:

f(ui) =

{2i 1 ≤ i ≤ n and i is odd2i− 1 1 ≤ i ≤ n and i is even,

f(u′i) =

{2i− 1 1 ≤ i ≤ n and i is odd2i 1 ≤ i ≤ n and i is even,

f(vi) =

{2n− 1 + 4i 1 ≤ i ≤

⌊n2

⌋and i is odd

2n− 3 + 4i 1 ≤ i ≤⌊n2

⌋− 1 and i is even,

f(vn+1−i) =

{2n+ 4i 1 ≤ i ≤

⌊n2

⌋and i is odd

2n− 2 + 4i 1 ≤ i ≤⌊n2

⌋− 1 and i is even,

and

f(v′i) =

f(vi)− 2 1 ≤ i ≤⌊n2

⌋and i is odd

f(vi) + 2⌊n2

⌋+ 2 ≤ i ≤ n and i is odd

f(vi) + 2 1 ≤ i ≤⌊n2

⌋− 1 and i is even

f(vi)− 2⌊n2

⌋+ 1 ≤ i ≤ n and i is even

The induced edge labeling is as follows:

f ∗(uiui+1) = 2i, for 1 ≤ i ≤ n− 1,

f ∗(uiu′i) = 2i− 1, for 1 ≤ i ≤ n,

f ∗(vivi+1) = 2n− 1 + 4i, for 1 ≤ i ≤⌊n2

⌋,

f ∗(vn+1−ivn−i) = 2n+ 4i, for 1 ≤ i ≤⌊n2

⌋− 1,

f ∗(viv′i) =

f(vi)− 2 1 ≤ i ≤⌊n2

⌋and i is odd

f(vi)⌊n2

⌋+ 2 ≤ i ≤ n and i is odd

f(vi) 1 ≤ i ≤⌊n2

⌋− 1 and i is even

f(vi)− 2⌊n2

⌋+ 1 ≤ i ≤ n and i is even

and

f ∗(ui+1vi) = 2n, for i =⌊n2

⌋+ 1.

Page 18: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

180 A. DURAI BASKAR, S. AROCKIARAJ AND B. RAJENDRAN

Case (iv) n ≡ 3(mod 4).We define f : V (G⊙K1) → {1, 2, 3, . . . , 4n} as follows:

f(ui) = 2i, for 1 ≤ i ≤ n, f(u′i) = 2i− 1, for 1 ≤ i ≤ n,

f(vi) =

{2n− 1 + 4i 1 ≤ i ≤

⌊n2

⌋and i is odd

2n− 3 + 4i 1 ≤ i ≤⌊n2

⌋+ 1 and i is even,

f(vn+1−i) =

{2n+ 4i 1 ≤ i ≤

⌊n2

⌋and i is odd

2n− 2 + 4i 1 ≤ i ≤⌊n2

⌋and i is even,

and

f(v′i) =

f(vi)− 2 1 ≤ i ≤⌊n2

⌋and i is odd

f(vi) + 1 i =⌊n2

⌋+ 1 and i is odd

f(vi)− 2⌊n2

⌋+ 3 ≤ i ≤ n and i is odd

f(vi) + 2 1 ≤ i ≤ n and i is even.

The induced edge labeling is as follows:

f ∗(uiui+1) = 2i, for 1 ≤ i ≤ n− 1,

f ∗(uiu′i) = 2i− 1, for 1 ≤ i ≤ n,

f ∗(vivi+1) = 2n− 1 + 4i, for 1 ≤ i ≤⌊n2

⌋,

f ∗(vn+1−ivn−i) = 2n+ 4i, for 1 ≤ i ≤⌊n2

⌋,

f ∗(viv′i) =

{f(vi)− 2 1 ≤ i ≤ n and i is oddf(vi) + 2 1 ≤ i ≤ n and i is even

and

f ∗(uivi) = 2n, for i =⌊n2

⌋+ 1.

Hence, f is a F -Geometric mean labeling of G ⊙ K1. Thus the graph G ⊙ K1 is aF -Geometric mean graph. �

A F -Geometric mean labeling of G⊙K1 is as shown in Figure 11.

Theorem 2.8. For a H−graph G, G⊙ S2 is a F -Geometric mean graph.

Proof. Let u1, u2, . . . , un and v1, v2, . . . , vn be the vertices of G. Therefore,

V [G⊙ S2] = V (G) ∪ {u′i, u

′′i , v

′i, v

′′i ; 1 ≤ i ≤ n}

and

E[G⊙ S2] = E(G) ∪ {uiu′i, uiu

′′i , viv

′i, viv

′′i ; 1 ≤ i ≤ n}.

Page 19: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

F -GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND THORN GRAPHS 181

s

s

s

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1313

★★★★

7

12

Figure 11. A F -Geometric mean labeling of H graph G⊙K1

Case (i) n is odd.We define f : V (G⊙ S2) → {1, 2, 3, . . . , 6n} as follows:

f(ui) = 3i− 1, for 1 ≤ i ≤ n,

f(u′i) = 3i− 2, for 1 ≤ i ≤ n,

f(u′′i ) = 3i, for 1 ≤ i ≤ n,

f(vi) = 3n− 2 + 6i, for 1 ≤ i ≤⌊n2

⌋,

f(vn+1−i) = 3n− 3 + 6i, for 1 ≤ i ≤⌊n2

⌋+ 1,

f(v′i) =

f(vi)− 2 1 ≤ i ≤⌊n2

f(vi)− 1 i =⌊n2

⌋+ 1

f(vi) + 2⌊n2

⌋+ 2 ≤ i ≤ n

and

f(v′′i ) =

{f(vi) + 2 1 ≤ i ≤

⌊n2

f(vi)− 2⌊n2

⌋+ 1 ≤ i ≤ n.

The induced edge labeling is as follows:

f ∗(uiui+1) = 3i, for 1 ≤ i ≤ n− 1,

f ∗(uiu′i) = 3i− 2, for 1 ≤ i ≤ n,

f ∗(uiu′′i ) = 3i− 1, for 1 ≤ i ≤ n,

f ∗(uivi) = 3n, for i =⌊n2

⌋+ 1,

Page 20: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

182 A. DURAI BASKAR, S. AROCKIARAJ AND B. RAJENDRAN

f ∗(vivi+1) = 3n+ 6i, for 1 ≤ i ≤⌊n2

⌋,

f ∗(vn+1−ivn−i) = 3n− 1 + 6i, for 1 ≤ i ≤⌊n2

⌋,

f ∗(viv′i) =

f(vi)− 2 1 ≤ i ≤⌊n2

f(vi)− 1 i =⌊n2

⌋+ 1

f(vi)⌊n2

⌋+ 2 ≤ i ≤ n

and

f ∗(viv′′i ) =

{f(vi) 1 ≤ i ≤

⌊n2

f(vi)− 2⌊n2

⌋+ 1 ≤ i ≤ n.

Case (ii) n is even.We define f : V (G⊙ S2) → {1, 2, 3, . . . , 6n} as follows:

f(ui) = 3i− 1, for 1 ≤ i ≤ n,

f(u′i) = 3i− 2, for 1 ≤ i ≤ n,

f(u′′i ) = 3i, for 1 ≤ i ≤ n− 1,

f(u′′n) = 3n+ 1,

f(vi) = 3n+ 1 + 6i, for 1 ≤ i ≤⌊n2

⌋− 1,

f(vn+1−i) = 3n+ 6(i− 1), for 2 ≤ i ≤⌊n2

⌋+ 1,

f(vn) = 3n+ 2,

f(v′i) =

{f(vi)− 2 1 ≤ i ≤

⌊n2

f(vi) + 2⌊n2

⌋+ 1 ≤ i ≤ n− 1,

f(v′n) = f(vn) + 1

and

f(v′′i ) =

f(vi) + 2 1 ≤ i ≤⌊n2

⌋− 1

f(vi)− 1 i =⌊n2

f(vi)− 2⌊n2

⌋+ 1 ≤ i ≤ n.

The induced edge labeling is as follows:

f ∗(uiui+1) = 3i, for 1 ≤ i ≤ n− 1,

f ∗(uiu′i) = 3i− 2, for 1 ≤ i ≤ n,

f ∗(uiu′′i ) = 3i− 1, for 1 ≤ i ≤ n,

f ∗(ui+1vi) = 3n + 1, for i =⌊n2

⌋,

f ∗(vivi+1) = 3n + 3 + 6i, for 1 ≤ i ≤⌊n2

⌋,

Page 21: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

F -GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND THORN GRAPHS 183

f ∗(vn+1−ivn−i) = 3n− 4 + 6i, for 2 ≤ i ≤⌊n2

⌋,

f ∗(vnvn−1) = 3n+ 3,

f ∗(viv′i) =

{f(vi)− 2 1 ≤ i ≤

⌊n2

f(vi)⌊n2

⌋+ 1 ≤ i ≤ n

and

f ∗(viv′′i ) =

f(vi) 1 ≤ i ≤⌊n2

⌋− 1

f(vi)− 1 i =⌊n2

f(vi)− 2⌊n2

⌋+ 1 ≤ i ≤ n.

Hence, f is a F -Geometric mean labeling of G ⊙ S2. Thus the graph G ⊙ S2 is aF -Geometric mean graph. �

A F -Geometric mean labeling of G⊙ S2 is as shown in Figure 12.

r

r

r

r

r

r

rr

r

r

r

r

r

r

✟✟✟✟PPPP

❍❍❍❍

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r

r

r

r

r

r

r

r

r

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910

1213

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r

✟✟✟✟PPPP

❍❍❍❍

r

r

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r

r

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r

r

r

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rr

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1 1

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rrr

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2523

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21 2726

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2424

25

Figure 12. A F -Geometric mean labeling of H graph G⊙ S2

Theorem 2.9. Ln ⊙K1 is a F -Geometric mean graph, for n ≥ 2.

Proof. Let V (Ln) = {ui, vi; 1 ≤ i ≤ n} be the vertex set of the ladder Ln andE(Ln) = {uivi; 1 ≤ i ≤ n} ∪ {uiui+1, vivi+1; 1 ≤ i ≤ n − 1} be the edge set of theladder Ln. Let wi be the pendent vertex adjacent to ui, and xi be the pendent vertexadjacent to vi, for 1 ≤ i ≤ n.

Page 22: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

184 A. DURAI BASKAR, S. AROCKIARAJ AND B. RAJENDRAN

We define f : V (Ln ⊙K1) → {1, 2, 3, . . . , 5n− 1} as follows:

f(u1) = 3,

f(v1) = 4,

f(x1) = 2,

f(ui) = 5i− 3, for 2 ≤ i ≤ n,

f(vi) = 5i− 2, for 2 ≤ i ≤ n,

f(wi) = 5i− 4, for 1 ≤ i ≤ n

and

f(xi) = 5i− 1, for 2 ≤ i ≤ n.

The induced edge labeling is as follows

f ∗(u1v1) = 3,

f ∗(v1x1) = 2,

f ∗(uivi) = 5i− 3, for 2 ≤ i ≤ n,

f ∗(wiui) = 5i− 4, for 1 ≤ i ≤ n,

f ∗(vixi) = 5i− 2, for 2 ≤ i ≤ n,

f ∗(uiui+1) = 5i− 1, for 1 ≤ i ≤ n− 1,

f ∗(vivi+1) = 5i, for 1 ≤ i ≤ n− 1.

Hence f is a F -Geometric mean labeling of Ln ⊙K1. Thus the graph Ln ⊙ K1 is aF -Geometric mean graph, for n ≥ 2. �

A F -Geometric mean labeling of L8 ⊙K1 is as shown in Figure 13.r r r r r r r r

r r r r r r r r

r r r r r r r r

r r r r r r r r

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3234

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38

39

Figure 13. A F -Geometric mean labeling of L8 ⊙K1

Theorem 2.10. Ln ⊙ S2 is a F -Geometric mean graph, for n ≥ 2.

Proof. Let V (Ln) = {ui, vi; 1 ≤ i ≤ n} be the vertex set of the ladder Ln andE(Ln) = {uivi; 1 ≤ i ≤ n} ∪ {uiui+1, vivi+1; 1 ≤ i ≤ n − 1} be the edge set of theladder Ln.

Page 23: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

F -GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND THORN GRAPHS 185

Let w(i)1 and w

(i)2 be the pendant vertices at each vertex ui, for 1 ≤ i ≤ n and x

(i)1

and x(i)2 be the pendant vertices at each vertex vi, for 1 ≤ i ≤ n. Therefore

V (Ln ⊙ S2) = V (Ln) ∪ {w(i)1 , w

(i)2 , x

(i)1 , x

(i)2 ; 1 ≤ i ≤ n}

and

E(Ln ⊙ S2) = E(Ln) ∪ {uiw(i)1 , uiw

(i)2 , vix

(i)1 , vix

(i)2 ; 1 ≤ i ≤ n}.

We define f : V (Ln ⊙ S2) → {1, 2, 3, . . . , 7n− 1} as follows :

f(ui) =

3 i = 17i− 2 2 ≤ i ≤ n and i is even7i− 5 3 ≤ i ≤ n and i is odd,

f(vi) =

5 i = 17i− 4 2 ≤ i ≤ n and i is even7i− 1 3 ≤ i ≤ n and i is odd,

f(w(i)1 ) =

{7i− 3 1 ≤ i ≤ n and i is even7i− 6 1 ≤ i ≤ n and i is odd,

f(w(i)2 ) =

2 i = 17i− 1 2 ≤ i ≤ n and i is even7i− 4 3 ≤ i ≤ n and i is odd,

f(x(i)1 ) =

{7i− 6 1 ≤ i ≤ n and i is even7i− 3 1 ≤ i ≤ n and i is odd,

f(x(i)2 ) =

6 i = 17i− 5 2 ≤ i ≤ n and i is even7i− 2 3 ≤ i ≤ n and i is odd.

The induced edge labeling is as follows:

f ∗(uiui+1) = 7i− 1, for 1 ≤ i ≤ n− 1,

f ∗(uivi) = 7i− 4, for 1 ≤ i ≤ n,

f ∗(vivi+1) = 7i, for 1 ≤ i ≤ n− 1,

f ∗(uiw(i)1 ) =

{7i− 3 1 ≤ i ≤ n and i is even7i− 6 1 ≤ i ≤ n and i is odd,

f ∗(uiw(i)2 ) =

{7i− 2 1 ≤ i ≤ n and i is even7i− 5 1 ≤ i ≤ n and i is odd,

f ∗(vix(i)1 ) =

{7i− 6 1 ≤ i ≤ n and i is even7i− 3 1 ≤ i ≤ n and i is odd,

and

f ∗(vix(i)2 ) =

{7i− 5 1 ≤ i ≤ n and i is even7i− 2 1 ≤ i ≤ n and i is odd.

Page 24: F-GEOMETRIC MEAN LABELING OF SOME CHAIN GRAPHS AND

186 A. DURAI BASKAR, S. AROCKIARAJ AND B. RAJENDRAN

Hence, f is a F -Geometric mean labeling of Ln ⊙ S2. Thus the graph Ln ⊙ S2 is aF -Geometric mean graph, for n ≥ 2. �

A F -Geometric mean labeling of L7 ⊙ S2 is as shown in Figure 14.

r r r r r r r

r r r r r r r

☞☞☞

✂✂✂

❏❏❏

r r r r r r r r r r r r r r

r r r r r r r r r r r r r r

1

1

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4 6 8 9 18 19 22 23 32 33 36 37 46 47

2 11 13 15 17 25 27 29 31 39 41 43 45

2 11 12 15 16 25 26 30 39 40 43 44296 13 20 27 34 41

12 16 26 30 40 44

10 17 24 31 38 45

7 10 14 20 21 24 28 34 35 38 42 48

5 8 9 18 19 22 23 32 33 36 37 46 47

Figure 14. A F -Geometric mean labeling of L7 ⊙ S2

References

[1] A. Durai Baskar, S. Arockiaraj and B. Rajendran, Geometric Mean Graphs, (Communicated).[2] J. A. Gallian, A dynamic survey of graph labeling, The Electronic Journal of Combinatorics,

17(2011).[3] F. Harary, Graph theory, Addison Wesely, Reading Mass., 1972.[4] R. Ponraj and S. Somasundaram, Further results on mean graphs, Proceedings of Sacoeference,

(2005), 443–448.[5] A. Rosa, On certain valuation of the vertices of graph, International Symposium, Rome, July

1966, Gordon and Breach, N. Y. and Dunod Paris (1967), 349–355.[6] S. Somasundaram and R. Ponraj, Mean labeling of graphs, National Academy Science Letter,

26(2003), 210–213.[7] S. Somasundaram and R. Ponraj, Some results on mean graphs, Pure and Applied Mathematika

Sciences, 58(2003), 29–35.[8] S. Somasundaram, P. Vidhyarani and R. Ponraj, Geometric mean labeling of graphs, Bulletin

of Pure and Applied sciences, 30E (2011), 153–160[9] S. Somasundaram, P. Vidhyarani and S. S. Sandhya, Some results on Geometric mean graphs,

International Mathematical Form, 7 (2012), 1381–1391.[10] R. Vasuki and A. Nagarajan, Further results on mean graphs, Scientia Magna, 6(3) (2010),

1–14.

Department of Mathematics,Mepco Schlenk Engineering College,Mepco Engineering College (Po) - 626 005Sivakasi, Tamilnadu, INDIA.E-mail address : [email protected], sarockiaraj [email protected],

[email protected]