Graph Powers and Graph Homomorphisms

In this paper we investigate some basic properties of fractional powers. In this regard, we show that for any rational number 1 ≤ 2r+1 2s+1 < og(G), G 2r+1 2s+1 −→ H if and only if G −→ H− 2s+1 2r+1 . Also, for two rational numbers 2r+1 2s+1 < 2p+1 2q+1 and a non-bipartite graph G, we show that G 2r+1 2s+1 < G 2p+1 2q+1 . In the sequel, we introduce an equivalent definition for circular chromatic number of graphs in terms of fractional powers. We also present a sufficient condition for equality of chromatic number and circular chromatic number.