A Note on [ r , s , c , t ] - Colorings of Graphs ∗ Jian - Ting Sheng † , Gui -
نویسندگان
چکیده
Let G be a simple graph with vertex set V(G) and edge set E(G). A subset S of V(G) is called an independent set if no two vertices of S are adjacent in G. The minimum number of independent sets which form a partition of V(G) is called chromatic number of G, denoted by χ(G). A subset S of E(G) is called an edge cover of G if the subgraph induced by S is a spanning subgraph of G. The maximum number of edge covers which form a partition of E(G) is called edge covering chromatic number of G, denoted by χ′c(G). Given nonnegative integers r, s, t and c, an [r, s, c, t]-coloring of G is a mapping f from V (G) ⋃ E(G) to the color set {0, 1, ..., k−1} such that the vertices with the same color form an independent set of G, the edges with the same color form an edge cover of G, and |f(vi)−f(vj)| ≥ r if vi and vj are adjacent, |f(ei)−f(ej)| ≥ s for every ei, ej from different edge covers, |f(vi)−f(ej)| ≥ t for all pairs of incident vertices and edges, respectively, and the number of edge covers formed by the coloring of edges is exactly c. The [r, s, c, t]-chromatic number χr,s,c,t(G) of G is defined to be the minimum k such that G admits an [r, s, c, t]-coloring. In this paper, we present the exact value of χr,s,c,t(G) when δ(G) = 1 or G is an even cycle.
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