In this paper,we obtain the thickness for some complete k-partite graphs for k=2,3.We first compute the thickness of K_(n,n+8)by giving a planar decomposition of K_(4k-1,4k+7)for k≥3.Then,two planar decompositions fo...In this paper,we obtain the thickness for some complete k-partite graphs for k=2,3.We first compute the thickness of K_(n,n+8)by giving a planar decomposition of K_(4k-1,4k+7)for k≥3.Then,two planar decompositions for K_(1,g,g)(g-1)when g is even and for K^(1,g,1/2(g-1)2)when g is odd are obtained.Using a recursive construction,we also obtain the thickness for some complete tripartite graphs.The results here support the long-standing conjecture that the thickness of K_(m,n)is[mn/2(m+n-2)]for any positive integers m,n.展开更多
Let P（G,A） be the chromatic polynomial of a graph G. A graph G is chromatically unique if for any graph H, P（H, λ） = P（G, λ） implies H is isomorphic to G. Liu et al. [Liu, R. Y., Zhao, H. X., Ye, C. F.： A com...Let P（G,A） be the chromatic polynomial of a graph G. A graph G is chromatically unique if for any graph H, P（H, λ） = P（G, λ） implies H is isomorphic to G. Liu et al. [Liu, R. Y., Zhao, H. X., Ye, C. F.： A complete solution to a conjecture on chromatic uniqueness of complete tripartite graphs. Discrete Math., 289, 175 179 （2004）], and Lau and Peng [Lau, G. C., Peng, Y. H.： Chromatic uniqueness of certain complete t-partite graphs. Ars Comb., 92, 353-376 （2009）] show that K（p - k,p - i,p） for i = 0, 1 are chromatically unique if p ≥ k ＋ 2 ≥ 4. In this paper, we show that if 2 〈 i 〈 4, the complete tripartite graph K（p - k,p - i,p） is chromatically unique for integers k ≥ i and p 〉 k2/4 ＋ i ＋ 1.展开更多
Let P（G,λ） be the chromatic polynomial of a simple graph G. A graph G is chromatically unique if for any simple graph H, P（H,λ） = P（G,λ） implies that H is isomorphic to G. Many sufficient conditions guarantee...Let P（G,λ） be the chromatic polynomial of a simple graph G. A graph G is chromatically unique if for any simple graph H, P（H,λ） = P（G,λ） implies that H is isomorphic to G. Many sufficient conditions guaranteeing that some certain complete tripartite graphs are chromatically unique were obtained by many scholars. Especially, in 2003, Zou Hui-wen showed that if n 〉 1/3m2 ＋ 3/1k2 ＋ 3/1mk＋ 1/3m-1/3k＋ 3/2√m2 ＋ k2 ＋ mk, where n,k and m are non-negative integers, then the complete tripartite graph K（n - m,n,n ＋ k） is chromatically unique （or simply χ–unique）. In this paper, we prove that for any non-negative integers n,m and k, where m ≥ 2 and k ≥ 0, if n ≥ 3/1m2 ＋ 3/1k2 ＋ 3/1mk ＋ 3/1m - 3/1k ＋ 43, then the complete tripartite graph K（n - m,n,n ＋ k） is χ–unique, which is an improvement on Zou Hui-wen’s result in the case m ≥ 2 and k ≥ 0. Furthermore, we present a related conjecture.展开更多
基金supported by the JSSCRC(Grant No.2021530)NNSFC under Grant No.12271392。
文摘In this paper,we obtain the thickness for some complete k-partite graphs for k=2,3.We first compute the thickness of K_(n,n+8)by giving a planar decomposition of K_(4k-1,4k+7)for k≥3.Then,two planar decompositions for K_(1,g,g)(g-1)when g is even and for K^(1,g,1/2(g-1)2)when g is odd are obtained.Using a recursive construction,we also obtain the thickness for some complete tripartite graphs.The results here support the long-standing conjecture that the thickness of K_(m,n)is[mn/2(m+n-2)]for any positive integers m,n.
文摘Let P（G,A） be the chromatic polynomial of a graph G. A graph G is chromatically unique if for any graph H, P（H, λ） = P（G, λ） implies H is isomorphic to G. Liu et al. [Liu, R. Y., Zhao, H. X., Ye, C. F.： A complete solution to a conjecture on chromatic uniqueness of complete tripartite graphs. Discrete Math., 289, 175 179 （2004）], and Lau and Peng [Lau, G. C., Peng, Y. H.： Chromatic uniqueness of certain complete t-partite graphs. Ars Comb., 92, 353-376 （2009）] show that K（p - k,p - i,p） for i = 0, 1 are chromatically unique if p ≥ k ＋ 2 ≥ 4. In this paper, we show that if 2 〈 i 〈 4, the complete tripartite graph K（p - k,p - i,p） is chromatically unique for integers k ≥ i and p 〉 k2/4 ＋ i ＋ 1.
基金Supported by the National Natural Science Foundation of China (Grant No.10771091)the Science and Research Project of the Education Department of Gansu Province (Grant No.0501-02)
文摘Let P（G,λ） be the chromatic polynomial of a simple graph G. A graph G is chromatically unique if for any simple graph H, P（H,λ） = P（G,λ） implies that H is isomorphic to G. Many sufficient conditions guaranteeing that some certain complete tripartite graphs are chromatically unique were obtained by many scholars. Especially, in 2003, Zou Hui-wen showed that if n 〉 1/3m2 ＋ 3/1k2 ＋ 3/1mk＋ 1/3m-1/3k＋ 3/2√m2 ＋ k2 ＋ mk, where n,k and m are non-negative integers, then the complete tripartite graph K（n - m,n,n ＋ k） is chromatically unique （or simply χ–unique）. In this paper, we prove that for any non-negative integers n,m and k, where m ≥ 2 and k ≥ 0, if n ≥ 3/1m2 ＋ 3/1k2 ＋ 3/1mk ＋ 3/1m - 3/1k ＋ 43, then the complete tripartite graph K（n - m,n,n ＋ k） is χ–unique, which is an improvement on Zou Hui-wen’s result in the case m ≥ 2 and k ≥ 0. Furthermore, we present a related conjecture.
