Cmjv01i05p0606

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J. Comp. & Math. Sci. Vol. 1(5), 606-616 (2010)

Edge Decomposition of the Transformation graph Gxyz when xyz =+ + 1

B. BASAVANAGOUD and 2PRASHANT V. PATIL 1 Corresponding Author, Department of Mathematics, Karnatak University,Dharwad-580 003, e-mail*: b.basavanagoud@gmail.com bgouder1@yahoo.co.in 2 Department of Mathematics, S D M College of Engg. and Tech., Dharwad-580 002, e-mail: prashant66.sdm@gmail.com

ABSTRACTS The transformation graph G    of G is the graph with vertex set

V (G )  E (G ) in which the vertices x and y are joined by an edge if one of the following conditions holds: (i) x, y  V (G ) and x and y are adjacent in G, (ii) x, y  E (G ) and x and y are adjacent in G, (iii) one of x and y is in V (G ) and the other is in E (G ) , and they are not incident in G. In this paper, for some standard class of graphs G, we establish the results on the decomposition of edges of the transformation graph G    into some standard class of graphs. 2000 Mathematics Subject Classification: 05C38(05C99) Keywords: Transformation graph, Edge decomposition.

INTRODUCTION All graphs considered here are finite, undirected, simple and standard. We refer to4 for unexplained terminology

and notations. Let G = (V (G ), E (G )) be a graph. V (G ) and E (G ) are called the vertex set and edge sets of G respectively. For two vetrices u and v

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B. Basavanagoud et al., J. Comp. & Math. Sci. Vol. 1(5), 606-616 (2010)

of G , if there is an edge e joining them, we say u and v are adjacent. In this case both u and v are end vertices of e , and u (or v ) and e are said to be incident. Two edges e and f are said to be adjacent if they have an end vertex in common. A graph is called hamiltonian if it has a spanning cycle. A spanning cycle is called hamiltonian cycle. A hamiltonian path in G is a path, which contains vertex of G . A decomposition of a graph G is a collection of subgraphs of G , whose edge set partition the edge set of G . The subgraphs of the decomposition are called the parts of the decomposition. A graph G is said to be F-decomposable or Fpackable if G has a decomposition in which all of its parts are isomorphic to graph F . The line graph L (G) of G is a graph whose vertex set is E (G ) in which two vertices are adjacent if and only if the edges are adjacent in G . The subdivision graph S1 (G ) of G is the graph with vertex set V (G )  E (G ) , two vertices of S1 (G ) are adjacent if and only if one of x, y is in V (G ) and other is in E (G ) and are incident in G . The total graph T (G ) of G is the graph whose vertex set is V (G )  E (G ) in which two vertices are adjacent if and only if they adjacent or incident in G . The complement of a graph G , denoted by G , is the graph with same vertex set as G and two vertices are adjacent if and only if they are not adjacent

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in G . Wu and Meng 6 generalized the concept of total graphs to a total transformation graph G xyz with    x, y , z {,} , where G is precisely the total graph of G , and G   is complement of G    . Each of these eight kind of transformation graphs G xyz were studied in6. W e shall investigate the transformation graph G    of a graph G . G    is the graph with vertex set V (G )  E (G ) , in which two vertices u and v are joined by an edge in G    if one of the following conditions holds: (i) u, v V (G ) and they are adjacent in G , (ii) u, v  E (G ) , and they are adjacent in G , and (iii) one of u and v is in V (G ) and other is in E (G ) , and they are not incident in G . In this paper, for some standard class of graphs G , we decompose the edges of the transformation graph G    into standard classes of graphs. Following results are used in the decomposition of the transformation graph G    of G . THEOREM A.[3].(Bermond) (i) If n is even, K n can be decomposed into n/2 hamiltonian paths. (ii) If n is odd, K n can be decomposed into (n  1)/2 hamiltonian cycles. If n is even , K n can be decomposed into (( n  2)/2)C n cycles of length n and ( n/2) K 2 ‘s. Remark 1.[5] Let G be a graph of

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V (G ) = n and E (G ) = m . Then V (G    ) = n  m , d G    ( x) = m , for any x  V (G ) and d    (e) = n  4  d (u )  d (v ) , for any G e = uv  E (G ) . Remark 2.[4] A connected graph is isomarphic to its line graph if and only if it is a cycle. Remark 3.[4] A graph G is the line graph of Kn if and only if 1) G has n(n - 1)/2 vertices, 2) G is regular of degree 2(n - 2) , 3) Every two nonadjacent points are mutually adjacent to exactly four points, 4) Every two adjacent points are mutually adjacent to exactly p - 2 points. Remark 4. If G = K1, n , then the line graph L(G) of G is the complete graph Kn. Remark 5.[1] For any graph G, G and

L (G ) are the edgedisjoint subgraphs of

RESULTS First, partition of edges of G    into edges of G, L(G) and stars for a given graph G. Proposition 2.1. Let G be a (p, q) graph. Then the edges of G    can be partitioned

E (G ) ,

edges of the line graph of G and the remaining edges corresponding to the point vertices are the edges of G. Hence the proposition. Next Theorm gives the partition of edges of G    into edges of G, a regular graph and stars, when G is a m-regular hamiltonian graph. Theorem 2.1 Let G be a m-regular hamiltonian graph with n vertices. Then the edges of G ++ – can be partitioned into G, (2(m -1)) regular graph on mn/2 vertices, (n - 2) regular graph on 2n vertices and (( mn/2)  n) times K1, n  2 . Proof. Let G be a m-regular hamiltonian graph with n vertices. Then the number of edges in G is mn /2 . Therefore in G    , n point vertices are of degree mn /2 and

mn/2 line vertices of degree ( n  2m  4) . Since, line graph L(G) of G is the

G  .

into

vertices there are q times K1, p  2 and the

E ( L(G )) and q times

E ( K1, p  2 ) . Proof. In G    , each line vertex is adjacent to (p - 2) point vertices and also with the line vertices which are adjacent edges in G. Therefore corresponding to q line

subgraph of G    and each line vertex is adjacent to 2(m -1) line vertices, hence edges of G    can be partitioned into 2(m -1) regular graph on mn/2 line vertices and the remaining edges can be partitioned as below. Consider n point vertices and n line vertices, which forms a cycle in G. Let H be a subgraph of G    formed by 2n vertices. In H, degree of a point vertex is m + (n - 2) and degree of line vertex is (n - 2). Therefore edges of this subgraph can be partitioned into edges of G and (n - 2)

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B. Basavanagoud et al., J. Comp. & Math. Sci. Vol. 1(5), 606-616 (2010)

-regular graph on 2n vertices. Now the remaining line vertices are ((mn/2) - n), which are adjacent to exactly (n - 2) point vertices. Therefore edges of G    can be partitioned into 2(m - 1) -regular graph on mn/2 vetices, edges of G, (n - 2) -regular graph on 2n vertices and (mn/2 - n) times

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Proof. In H the central vertex of G is not adjacent to any line vertices and each line vertex is adjacent to exactly n  1 point vertices and n  1 line vertices. Hence H can be partitioned into n times K1,n , one

K1,n and one K n .

K1, n 2 .

Proposition 2.3. Let G = K1, n and

Corollary 2.1.1 Let G be a cycle Cn. Then

H = G    . Consider the point vertices of

the edges of G    can be partitioned into 2Cn and (N - 2) -regular graph on 2n vertices. Proof. In Theorem 2.1, take m = 2 . The number of edges of G is n. The number of

G, which are not central vertices, then edges of H can be partitioned into n times

vertices of G    is 2n and the degree of point vertices and line vertices is n in G    . Edges of

G    can be partitioned into

G = C n , L(G) = C n and (n - 2) -regular graph on 2n vertices. Next, we give the edge decomposition of

G    , when G = C n , Pn , K n , K n ,n , K 1, n . Proposition 2.2. Let

G = K1, n and

K1,n and on line vertices one K n . Proof. In H, each point vertex, which is not a central vertex of G is adjacent to exactly n  1 line vertices and one point vertex which is the central vertex of G, and each line vertex is adjacent to exactly n  1 line vertices. Hence H can be partitioned into n times K1,n and one K n . In the following theorem we partition the edges of G    into cycles of different lengths, when G is cycle.

partitioned into n times K1, n 1 , such that

Theorem 2.2 Let G = C n and H = G    . Then the edges of H can be partitioned into

any two K1, n 1 have

n  2 common

(a) 2C n , (( n  3)/2)C 2 n and nK 2 , if n is odd.

vertices, one K1,n , such that K1, n 1 and

(b) 2C n and (( n  2)/2)C 2 n , if n is even.

H = G    . Then the edges of H can be

K1,n have n  1 common vertices and one complete graph K n , such that the vertices of K n and centers of K1, n 1 are common vertices.

Proof. Let G = C n . Then H has n point vertices with degree n and n line vertices with degree n. Case 1. When n is even. Let

v1 , v 2 ,...., v n be the point vertices

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e12 , e23 ,...., e( n 1) n , be the line vertices in H.

v j , j = 1,2,3,...., n . Consider the point vertex v1 . v1 is

In H each v j is adjacent to n  2 line vertices

adajacent to

e12 , e23 ,...., e( j  2)( j 1) , e( j 1)( j  2) ,...., e( n 1) n , en1.

combine these into (e23 , e34 ) ; (e45 , e56 ) ;....;

Combining these line vertices in two’s as

(e( n 2)( n 1) , e( n 1) n ) . We get the ( n  2)/2

n is even. There are ( n  2)/2 such

cycles of length 2 n in G    as follows.

collections, which are adjacent to

v

v

1

e

v 2

e

12

23

e

3

34

v

e23 , e34 ,...., e( n 1) n . Now

v

4

e

45

e

n- 2

(n -2 )( n- 1)

v

e

n -1

v

n

e

n1

(n -1 )n

1. v1e( n 1) n v2 en1v3e12 v4 .....vn e( n  2)( n 1) v1 . 2. v1e( n  3)( n  2) v2 e( n  2)( n 1) v3 e( n 1) n v4 en1v5 e12 v6 e23 .....vn e( n  4)( n 3) v1 . 3. v1e( n 5)( n  4) v2 e( n  4)( n  3) v3e( n 3)( n  2) v4 e( n  2)( n 1) v5e( n 1) n v6 en1v7 e12 .....vn e( n  6)( n  5) v1 . .

.

.

.

.

.

(n-2)/2. v1e34 v2 e45 v3e56 v4 e67 .....vn e23v1 . From this construction and by Remark 2, it follows that edges of G    is the union of edges of G = C n , edges of L(G ) = C n and the edges of cycles (( n  2)/2)C 2 n . Journal of Computer and Mathematical Sciences Vol. 1, Issue 5, 31 August, 2010 Pages (528-635)


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Case 2. When n is odd. There are n point vertices

v1 , v 2 ,...., v n

and

n

line

e12 , e23 ,...., en1 . Combine

vertices

( n  1) line

vertices into group of two's. v1 is adjacent to

e23 , e34 ,....., e( n 1) n . Leaving e( n 1) n

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if n is odd. (b)

K 1, n , (( n  2)/2)C n , (( n  2)/2 )C 2 n

and (3n/2) K 2 , if n is even. Proof. Let G = K1, n . Then G    has n  1 point vertices each of degree n and n line vertices with degree

2(n  1) . Let

combine these into

v1 , v2 ,....vn , v be the point vertices and

(e23 , e34 ); (e45 , e56 )....; (e( n 3)( n  2) , e( n 2)( n 1) ) .

e1 = vv1 , e2 = vv2 ,....en = vvn  E (G ) be the

Similarly v2 is adjacent to

n line vertices, where v is the central node of G. Case 1. When n is odd.

(e34 , e45 ); (e56 , e67 )....; ( e( n  2)( n 1) , e( n 1) n ) and

en1. As in Case 1, there are (( n  1)  2 ) / 2 cycles of length 2 n and nK 2 's,

In G    , each v j is adjacent to n  1 line vertices e1 , e 2 ,...., e j 1 , e j 1 ,....., en and is

v1e( n 1) n , v2 en1 , v3 e12 ,.....vn e( n  2)( n 1) . be

adjacent to one point vertex v . Combining these line vertives into two by two. Thus

partitioned into G = C n , L(G ) = C n and

there are ( n  1)/2 such collections , which

((n  3)/2)C 2 n and nK 2 .

are adjacent to v j , for j = 1,2,...., n .

Theorem 2.3 Let G = Pn and H = G    , then the edges of H can be partitioned into

Consider v1 , combine the edges as

(a) Pn , Pn 1 , (( n  3)/2) P2 n 1 and (n  1) K 2

be obtained as follows:

Therefore the edges of

G

   can

if n is odd. (b)

(e2 , e3 ); (e4 , e5 );.....(en 1 , en ) . The ( n  1)/2 cycles of length 2 n in G    can 1. v1e3v2 e4 v3e5 .....en vn 1e1vn e2 v1 .

Pn , Pn1 , ((n  2)/2) P2 n1 if n is even.

Proof. Similar to Theorem 2.2.

2. v1e5 v2 e6 v3e7 .....en vn 3e1vn  2 e2 vn 1e3vn e4 v1 . .

.

cycles and stars.

.

.

Theorem 2.4 If G = K1, n , then the edges

((n-1)/2) v1en v2 e1v3 e2 .....vn en 1v1 .



Next we partition the edges of K1,n into

of G    can be partitioned into (a) K 1, n , ( ( n  1)/2 )C n and (( n  1)/2)C 2 n ,

From this construction and from the definition of G    , it follows that edges of

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G    can be partitioned into G = K1, n ,

length n and (n/2) K 2 's. Thus by Theorem

( n  1)/2 cycles of length 2 n and by

A,

Remark 4, a complete graph K n on line

K 1, n , (( n  2)/2)C n , (( n  2)/2 )C 2 n and

vertices, which can be further partitioned

(3n/2) K 2 's.

into

( n  2)/2 cycles of length n, by

Theorem A. Case 2. When n is even. Since each point vertex v j in G    is adjacent to n  1 line vertices,

e1 , e 2 ,...., e j 1 , e j 1 ,....., en therefore among these, n  2 line vertices can be grouped into pairs. Consider v1 . v1 is adjacent to n  1 line vertices e2 , e3 ,...., en 1 , en . Leaving en , we get ( n  2)/2 pairs

(e2 , e3 ); (e4 , e5 );.....; (e n2 , e n1 ) . Similarly

v2 is adjacent to e1 , e3 ,...., en1 , en leaving e1 , we get ( n  2)/2 pairs (e3 , e 4 ); (e5 , e6 );.....; (e n1 , e n ) . Therefore as in Case 1, there are

can be partitioned into

G 

In next theorems we partition

( K n )    into cycles, stars and regular graphs. Lemma 1. If G = K n , then the edges of the line graph L (G ) of G can be partitioned into (a) (( n  1)/2)C n and nK 1,2( n  3) , when n is odd. (b)

(( n  2)/2 )C n , nK 1,2( n  4) and (n/2) K1,2( n  2) , when n is even.

G = K n . Then L (G ) is a

Proof. Let

2(n  2) -regular graph on (n( n  1)) /2 vertices. Case 1. When n is odd. By

A, K n can

Theorem

be

decomposed into (( n  1)/2)C n , hence by

(n  2)/2 cycles of length 2 n and nK 2 's

Remark

given by v1en , v2 e1 , v3e2 .....vn en 1 . Hence by

into (( n  1)/2)C n . Consider n vertices

definition of

2,

L (G )

is

partitioned

G    and from above

which form a cycle C n is L (G ) , each of

construction G    can be partitioned into

these n vertices are adjacent with

G = K1, n , ( n  2)/2 cycles of length

2(n  2)  2 = 2( n  3) vertices of other

2n, nK 2 and one complete graph K n on

cycles in L( K n ) , hence nK 1,2( n  3) .

line vertices. By Remark 4, which can be

Case 2. When n is even.

further partitioned into ( n  2)/2 cycles of

By

Theorem

A, K n can

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be


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((n  2)/2)C n and

decomposed into

((n  2)/2)C n , ((n  2)/2)((n  2)/2)C 2n

(n/2) K 2 . Hence by Remark 2. L (G) can

and L( K n ) . But by Lemma 1, L( K n ) is

be partitioned into (( n  2)/2)C n . Consider

partitioned into (( n  2)/2 )C n , nK 1,2( n  4)

n vertices which forms a cycle C n in L (G ) ,

and (n/2) K1,2( n  2) .

each of these n vertices are adjacent with

2( n  2)  4 = 2( n  4) vertices of other

Now consider (n/2) K 2 's on G. In

cycles in L (G ) , thus nK1,2( n  4) and the

G    , (n/2) line vertices are adjacent to exactly n  2 point vertices. Therefore, in

remaining (n/2) K 2 's in G, will have (n/2)

G    there are ( n/2) K1,n  2 and (n/2) K 2 .

vertices in L (G ) which are adjacent to

Hence from the above,

2( n  2) vertices of

partitioned into

L (G ) , hence

G    can be

( n/2) K1,2( n  2) .

(n  2)Cn , ((n  2) 2 /4)C2 n , nK1,2( n 4) ,

Theorem 2.5 If G = K n , then the edges

(n/2) K1,2( n 2) , (n/2) K1, n 2 and (n/2) K 2 .

of G    can be partitioned into

Case 2. When n is odd.

2

(a) (n  2)C n , ((n  2) /4)C2 n , nK1,2( n 4) ,

(n/2) K1,2( n 2) , (n/2) K1, n 2 and

(n/2) K 2 ,

when n is even. (b) (n  1)C n , (( n  1)( n  3)/4)C2 n , nK 1,2( n 3)

The edges of

K n can be

partitioned into (( n  1)/2)C n . Therefore by Proposition 1. and Theorem 2.2, edges of

G    can be partitioned into ((n  1)/2)C n ,

((n  1)/2)((n  3)/2)C 2 n , (n(n  1)/2) K 2

and (n(n  1)) K 2 , when n is odd.

and L( K n ) . But by Lemma 1, L( K n ) can

Proof. Let G = K n . Then

be partitioned into (( n  1)/2 )C n , nK 1,2( n 3) .

G    has n point vertices, each of degree (n( n  1)/2) and (n( n  1)/2) line vertices each of degree 3( n  2) . Case 1. When n is even.

Thus, G   

can be partitioned into

(n  1)C n , (( n  1)( n  3)/4 )C 2 n , nK 1,2( n 3) and (n(n  1)) K 2 .

The edges of K n can be partitioned

Theorem 2.6 If G = K n with n > 3 , then

into (( n  2)/2)C n and (n/2) K 2 's. Therefore

the edges of G    can be partitioned into

by Proposition 2.1, and by Theorem 2.2,

(a) ( n  1)/2 times (n  2) -regular graph

edges of G    can be partitioned into

on 2 n vertices, with n point vertices are

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common to all of these regular graphs,

2(n  2) -regular graph on

n( n  1)/2

of G    , K n is also a subgraph of G    . Case 2. When n is even.

vertices and K n , when is odd.

Edges of K n can be partitioned into

(b) ( n  2)/2 times (n  2) -regular graph

( n  2)/2 cycles of length n and (n/2)K 2 .

on 2 n vertices with n point vertices are common to all of these regular

In G    each line vertex is adjacent to

graphs, 2(n  2) -regular

graph

on

n( n  1)/2 vertices, K n and ( n/2) K1,n  2 , when n is even. Proof. Let G = K n . Then G   

( n  2) point vertices and also with 2( n  2) line vertices. Now, consider n line vertices which forms n-cycles in G. These n line vertices and n point vertices forms

has n

a ( n  2) -regular graph on 2n vertices.

point vertices each of degree n( n  1)/2

Hence, corresponding to ( n  2)/2 cycles

and n( n  1)/2 line vertices each of degree

of length n in G, there exists ( n  2)/2

3( n  2) .

times ( n  2) -regular graph on 2n vertices

Case 1. When n is odd.

such that n point vertices are in common to these regular graphs. Also each line

Edges of K n can be partitioned into

( n  1)/2 cycles of length n. In G    , each line vertex is adjacent to ( n  2) point vertices and 2( n  2) line vertices. Now,,

vertex is adjacent with 2( n  2) line vertices. Corresponding to n( n  1)/2 line vertices, there exists

2( n  2) -regular

consider n line vertices which form a n-

graph. Now, consider (n/2)K 2 's in G. In

cycle in G and n point vertices in G    . These 2n vertices form a ( n  2) -regular

G    these n/2 line vertices are adjacent to ( n  2) point vertices. Therefore in G    ,

graph on 2n vertices. Corresponding to

there are

( n  1)/2 exists

cycles of length n in G, there

( n  1)/2 times ( n  2) -regular

graph on 2n vertices such that n point vertices are common in all of these regular graphs. Also each line vertex is adjacent with 2( n  2) line vertices. Corresponding to these n( n  2)/2 line vertices there exists s

( 2(n  2)) -regular graph. And by definition

( n/2) K1,( n  2) and also by

definition of G    , K n

is also induced

subgraph of G    . Theorem 2.7 If G = K n , n , edges of G    can be partitioned into (a) nC2 n , (n( n  1)/2)C4 n and

(n 2 (n  2) 4) K1, 4 if n is even.

Journal of Computer and Mathematical Sciences Vol. 1, Issue 5, 31 August, 2010 Pages (528-635)


B. Basavanagoud et al., J. Comp. & Math. Sci. Vol. 1(5), 606-616 (2010)

(b)

2

2

(n 1)C2n , ((n  1) /2)C4n , n(n 1) 4 K1,4, nK1, 2 ( n 1) and nK2 if n is odd. Proof. Let G = K n , n . Then G    has 2n point vertices, each of degree n2 and n2 line vertices each of degree (4n  4) .

615

(2(n  1)/2)C 2n , ((n  1)/2(2n  2)/2)C4 n and by considering two cycles of lenth 2n from G, each line vertex corresponding to one C2 n is adjacent to 4 line vertices of other C2 n in G    . Hence 2nK1, 4 . But in

 (n  1) 2   combinations of 2  

Case 1. When n is even.

G, there are 

The edges of K n , n can be partitioned into

two cycles of length

(n/2)C2n . Therefore by Theorem 2.2,

n(n  1)(n  3) 4 K1, 4 .

2n. Therefore

egdes of (C 2n )    can be partitioned into

Now, consider the edges of nK2

2C2 n , ((2n  2)/2)C4 n . Hence G    can be

in G, in G    n line vertices are adjacent to

partitioned into

4 line vertices of each C2 n therefore

2(n/2)C2 n , (n/2)((2n  2)/2)C 4n

n(n  1) / 2K1,4

and by considering two cycles of lenth 2n from G, each line vertex corresponding to

are adjacent with (2n  2) point vertices.

one C2 n is adjacent to 4 line vertices of other C2 n in G    . Hence 2nK1, 4 . But in

n 2  combinations of two G, there are   2  cycles

of

length

2n.

Therefore

(n 2 (n  2) 4) K1, 4 . Hence G    can be

and these n line vertices

Hence G    can be partitioned into

(n  1)C 2n ,

((n  1) 2 /2)C4 n , n(n  1) 2 4 K1,4 , nK1, 2 ( n 1) and nK2 . REFERENCES 1. B. Basavanagoud, Keerti M. and Malghan S.H., On trnasformation

((n  1)/2)C2 n , nK 2 .Therefore by Theorem

graph G xyz when xyz =    , (Proc) Graph theory and its applications, Macmillan Publishers, India Ltd.123130 (2009). 2. B. Basavanagoud, Keerti M. and Malghan S.H., Traversability and planarity of the trnasformation graph

2.2, (C 2n )    can be partitioned into

G xyz when xyz =    , (Proc) Graph

partitioned into nC2 n , ( n( n  1)/2)C 4 n and

(n 2 (n  2) 4) K1, 4 . Case 2. when n is odd. The edges of K n.n can be partitioned into

Journal of Computer and Mathematical Sciences Vol. 1, Issue 5, 31 August, 2010 Pages (528-635)


616

B. Basavanagoud et al., J. Comp. & Math. Sci. Vol. 1(5), 606-616 (2010)

theory and its applications, Macmillan Publishers, India Ltd. , 153-165 (2009). 3. J. C. Bermond , Hamilton decomposition of graphs and hypergraphs, In advances in Graph Theory (ed.B.bollabas), North Holland, Amsterdam, pp.21-28 (1978). 4. F. Harary, Graph Theory, Addison-

Wesley, Reading, Mass, (1969). 5. Lei Yi and B. Wu, The transformation graph G    , Aust. J. of Combinatorics, Vol.44, 37-42 (2009). 6. B. Wu and J. Meng, Basic properties of total transformation graphs, J. Math. Study, 34(2), 109-116 (2001).

Journal of Computer and Mathematical Sciences Vol. 1, Issue 5, 31 August, 2010 Pages (528-635)


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