1. Introduction
Let be a graph with
vertex set and edge set . We denote the maximum degree of
by . The first paper on edge
coloring was written by Tait in 1880. Since all edges incident to the
same vertex must be assigned different colors, obviously .
In 1964, Vizing [1]
proved that . In 1973, Meyer [2] presented the concept of equitable coloring
and equitable chromatic number. The idea of equitable edge coloring was
defined by Hilton and de Werra [3] in 1994. It is the assignment of colors to all
the edges of , so that the edges
can be partitioned into color classes with the difference between any
two classes is atmost one.
Sampathkumar et.al [4]
introduced the concept of splitting graph of a graph denoted by . It is framed by adding to each
vertex , a new vertex such that is adjacent to every vertex
that is adjacent to in . We construct the splitting graph of
some families of wheel graph and obtain the equitable edge coloring of
such graphs.
In our day to day life many problems on optimization, network
designing, scheduling problems, allocation of memory in computer
networks and so on are related to edge coloring. For example, consider
the time-tabling problem for the proper utilization of facilities, i.e.,
the minimum number of rooms needed at any one time can be scheduled by
equitable edge coloring. In this paper, we determine the equitable edge
chromatic number for splitting graph of , and .
2. Preliminaries
Theorem 1. [1] Let be a
graph. Then .
Definition 1. [5] For any integer , the wheel graph is the -vertex graph obtained by joining a
vertex to each of the vertices of the cycle
graph .
Definition 2. [6] A double-wheel graph of size can be composed of , which consists of two
cycles of size , where the
vertices of the two cycles are all connected to a common hub.
Definition 3. The gear graph is the graph obtained from a wheel
graph by adding a vertex to
each edge of the cycle in .
Definition 4. [4] For each vertex of a graph , take a new vertex . Join to all vertices of adjacent to . The graph thus obtained is called the
splitting graph of .
Definition 5. [3,7,8] An equitable edge coloring of a graph
is a -proper edge coloring , if , ,
where , is the set of edges of
color and repectively. The minimum of such is called the equitable edge chromatic
number of and is denoted by .
Lemma 1. [9]For any simple graph , .
Lemma 2. [9] For any simple graph and , and if then , where is the proper
edge chromatic number of .
Lemma 3. [10] Let be a
graph and let . If for each , then has an equitable edge-coloring with
colors.
Lemma 4. [10] Let be a
graph and let . If the -core of is a set of isolated vertices, then
has an equitable edge-coloring
with colors.
Additional graph theory terminology used in this paper can be found
in [1].
In the following section, the equitable edge chromatic number of
wheel , double wheel and gear graph are determined.
3. Equitable
edge coloring of wheel, double wheel and gear graphs
Theorem 2. The equitable edge chromatic number
of splitting graph of wheel graph is , for .
Proof. The wheel graph consists of vertices and edges. Let where is the edge ,
is the edge , is the edge and is
the edge .
For the construction of splitting graph of wheel graph, new vertices
and edges are chosen. It consists of vertices and edges. Let
The edges between the
vertices of the splitting graph of wheel graph are tabulated as
follows:
Table 1. Classification of edges of
Divisions of |
Values of |
Ranges of |
Edges between |
|
|
|
the vertices |
|
0 |
|
|
|
1 |
|
, |
|
2 |
|
|
|
3 |
|
|
|
4 |
|
|
|
5 |
|
|
|
6 |
|
|
The coloring of edges is defined as By this procedure, the assignment of colors to
all the edges is attained with colors. The edges of splitting
graph of wheel graph are classified into independent color classes as
such that for any . Hence it is clear that for , thus satisfying equitablility
condition. Therefore . Since and by lemma 1, it
follows that . Hence . 
Theorem 3. The equitable edge chromatic number
of splitting graph of double wheel graph is , for .
Proof. The double wheel graph consists of vertices and edges. and
where is the edge ,
is the edge , is the edge , is the
edge , is the edge ,
is the edge , is the edge and is
the edge .
The splitting graph of double wheel graph is constructed by adding
new vertices and edges, which consists of vertices and edges. Let and The edges of the splitting graph of
double wheel graph lying between the vertices are summarized as
follows:
Table 2. Classification of edges of
Divisions of |
Values of |
Ranges of |
Edges between |
|
|
|
the vertices |
|
0 |
|
|
|
1 |
|
, |
|
2 |
|
|
|
3 |
|
|
|
4 |
|
|
|
5 |
|
|
|
6 |
|
|
|
6 |
|
|
|
7 |
|
, |
|
8 |
|
|
|
9 |
|
|
|
10 |
|
|
|
11 |
|
|
|
12 |
|
|
The coloring of edges is defined as
All the edges of this splitting graph are assigned colors by the
above process with different
colors. The edges are classified into such that each of the
independent sets for any . It is clear that for , thus satisfying equitablility
condition. Hence it is observed that . By lemma 1, it follows that .
Therefore . 
Theorem 4. The equitable edge chromatic number
of splitting graph of gear graph is , for .
Proof. The gear graph consists of vertices and edges. Let where
is the edge , is the edge , is the edge and is the edge .
The construction of splitting graph of gear graph consists of vertices and edges. Let and
The edges connecting
each of the vertices of the splitting graph of gear graph is obtained by
substituting and are
tabulated as follows:
Table 3. Classification of edges of
0 |
|
|
1 |
|
|
2 |
|
, |
3 |
|
|
4 |
|
, |
5 |
|
|
6 |
|
|
7 |
|
|
8 |
|
, |
The edge coloring of splitting graph of gear graph is defined as
By the above method of coloring all the edges of
the splitting graph of gear graph are allocated with colors. The edges are classified
into such that each of the independent
sets and for all . Hence it is observed that for , satisfying equitablility
condition. This implies . By lemma 1, it follows that .
Therefore . 
4. Conclusion
In this paper, the equitable edge chromatic number of wheel graph
families such as wheel , double
wheel and gear graph are obtained, the proofs provides an
optimal solution to the equitable edge coloration of these splitting
graphs. The equitable edge coloring in the area of splitting graphs and
other product graphs is vast explorable and the focus on the
determination of equitability in allocation can be extended to other
families of graphs.
Acknowledgements
The authors sincerely thank the Referee for the careful reading,
corrections and suggestions that have resulted in the improvement of the
quality of this manuscript.
Conflict of Interest
The author declares no conflict of interests.