5,351 research outputs found
On The b-Chromatic Number of Regular Graphs Without 4-Cycle
The b-chromatic number of a graph , denoted by , is the largest
integer that admits a proper -coloring such that each color class
has a vertex that is adjacent to at least one vertex in each of the other color
classes. We prove that for each -regular graph which contains no
4-cycle, and if has a triangle,
then . Also, if is a -regular
graph which contains no 4-cycle and , then .
Finally, we show that for any -regular graph which does not contain
4-cycle and ,
Dynamic Chromatic Number of Regular Graphs
A dynamic coloring of a graph is a proper coloring such that for every
vertex of degree at least 2, the neighbors of receive at least
2 colors. It was conjectured [B. Montgomery. {\em Dynamic coloring of graphs}.
PhD thesis, West Virginia University, 2001.] that if is a -regular
graph, then . In this paper, we prove that if is a
-regular graph with , then . It confirms the conjecture for all regular graph with
diameter at most 2 and . In fact, it shows that
provided that has diameter at most 2 and
. Moreover, we show that for any -regular graph ,
. Also, we show that for any there exists a
regular graph whose chromatic number is and .
This result gives a negative answer to a conjecture of [A. Ahadi, S. Akbari, A.
Dehghan, and M. Ghanbari. \newblock On the difference between chromatic number
and dynamic chromatic number of graphs. \newblock {\em Discrete Math.}, In
press].Comment: 8 page
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