- Harmonious coloring
In
graph theory , a harmonious coloring is a (proper) vertex coloring in which every pair of colors appears on at most one pair of adjacent vertices. The harmonious chromatic number χH("G") of a graph "G" is the minimum number of colors needed for any harmonious coloring of "G".Every graph has a harmonious coloring, since it suffices to assign every vertex a distinct color; thus χH("G") ≤ |V(G)|. There trivially exist graphs "G" with χH("G") > χ("G") (where χ is the
chromatic number ); one example is the path of length 2, which can be 2-colored but has no harmonious coloring with 2 colors.Some properties of χH("G"):
# χH(T"k",3) = ⌈(3/2)("k"+1)⌉, where T"k",3 is the complete "k"-ary tree with 3 levels. (Mitchem 1989)Harmonious coloring was first proposed by Frank, Harary and Plantholt (1982).Still very little is known about it.
See also:
Complete coloring External links
* [http://www.maths.dundee.ac.uk/~kedwards/biblio.html] "A Bibliography of Harmonious Colourings and Achromatic Number" by Keith Edwards
References
* Frank, O.; Harary, F.; Plantholt, M. (1982). The line-distinguishing chromatic number of a graph. "Ars Combin." 14, 241–252.
* Jensen, Tommy R.; Toft, Bjarne (1995). "Graph coloring problems". New York: Wiley-Interscience. ISBN 0-471-02865-7.
* Mitchem, J. (1989). On the harmonious chromatic number of a graph. "Discrete Math." 74, 151–157.
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