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arXiv 1104.4411math.CO
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关于图幂的染色性质

On Coloring Properties of Graph Powers

Hossein Hajiabolhassan, Ali Taherkhani

摘要:

本文研究了图的幂的一些染色性质。我们证明了$χ_c(G^{^{\frac{2r+1}{2s+1}}})=\frac{(2s+1)χ_c(G)}{(s-r)χ_c(G)+2r+1}$,条件是$χ_c(G^{^{\frac{2r+1}{2s+1}}})< 4$。因此,可以看到,如果${2r+1 \over 2s+1} \leq {χ_c(G) \over 3(χ_c(G)-2)}$,则$χ_c(G^{^{\frac{2r+1}{2s+1}}})=\frac{(2s+1)χ_c(G)}{(s-r)χ_c(G)+2r+1}$。特别地,$χ_c(K_{3n+1}^{^{1\over3}})={9n+3\over 3n+2}$和$K_{3n+1}^{^{1\over3}}$不存在圆色数等于${6n+1\over 2n+1}$的子图。这对[Xuding Zhu,Circular色数:a survey,Discrete Math.,229(1-3):371- 410,2001]。同时,我们给出了剖分图的分数色数的一个上界。准确地说,我们表明,$χ_f(G^{^{\frac{1}{2s+1}}})\leq \frac{(2s+1)χ_f(G)}{sχ_f(G)+1}$。最后,我们研究了细分图的$n$阶多色数。

英文摘要:

This paper studies some coloring properties of graph powers. We show that $χ_c(G^{^{\frac{2r+1}{2s+1}}})=\frac{(2s+1)χ_c(G)}{(s-r)χ_c(G)+2r+1}$ provided that $χ_c(G^{^{\frac{2r+1}{2s+1}}})< 4$. As a consequence, one can see that if ${2r+1 \over 2s+1} \leq {χ_c(G) \over 3(χ_c(G)-2)}$, then $χ_c(G^{^{\frac{2r+1}{2s+1}}})=\frac{(2s+1)χ_c(G)}{(s-r)χ_c(G)+2r+1}$. In particular, $χ_c(K_{3n+1}^{^{1\over3}})={9n+3\over 3n+2}$ and $K_{3n+1}^{^{1\over3}}$ has no subgraph with circular chromatic number equal to ${6n+1\over 2n+1}$. This provides a negative answer to a question asked in [Xuding Zhu, Circular chromatic number: a survey, Discrete Math., 229(1-3):371--410, 2001]. Also, we present an upper bound for the fractional chromatic number of subdivision graphs. Precisely, we show that $χ_f(G^{^{\frac{1}{2s+1}}})\leq \frac{(2s+1)χ_f(G)}{sχ_f(G)+1}$. Finally, we investigate the $n$th multichromatic number of subdivision graphs.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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