Citation
Omoomi, Behnaz
(2001)
Chromatic Equivalence Classes and Chromatic Defining Numbers of Certain Graphs.
PhD thesis, Universiti Putra Malaysia.
Abstract
There are two parts in this dissertation: the chromatic equivalence classes and
the chromatic defining numbers of graphs.
In the first part the chromaticity of the family of generalized polygon trees with
intercourse number two, denoted by Cr (a, b; c, d), is studied. It is known that
Cr( a, b; c, d) is a chromatic equivalence class if min {a, b, c, d} ≥ r+3. We consider
Cr( a, b; c, d) when min{ a, b, c, d} ≤ r + 2. The necessary and sufficient conditions
for Cr(a, b; c, d) with min {a, b, c, d} ≤ r + 2 to be a chromatic equivalence class
are given. Thus, the chromaticity of Cr (a, b; c, d) is completely characterized.
In the second part the defining numbers of regular graphs are studied. Let
d(n, r, X = k) be the smallest value of defining numbers of all rregular graphs
of order n and the chromatic number equals to k. It is proved that for a given
integer k and each r ≥ 2(k  1) and n ≥ 2k, d(n, r, X = k) = k  1. Next,
a new lower bound for the defining numbers of rregular kchromatic graphs
with k < r < 2( k  1) is found. Finally, the value of d( n , r, X = k) when
k < r < 2(k  1) for certain values of n and r is determined.
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