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De Ming Li 《数学学报(英文版)》2002,18(1):173-180
The notion of the star chromatic number of a graph is a generalization of the chromatic number. In this paper, we calculate
the star chromatic numbers of three infinite families of planar graphs. The first two families are derived from a 3-or 5-wheel
by subdivisions, their star chromatic numbers being 2+2/(2n + 1), 2+3/(3n + 1), and 2+3(3n−1), respectively. The third family of planar graphs are derived from n odd wheels by Hajos construction with star chromatic numbers 3 + 1/n, which is a generalization of one result of Gao et al.
Received September 21, 1998, Accepted April 9, 2001. 相似文献
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图的星色数是通常色数概念的推广.本文求出了几类由轮图导出的平面图的星色数.前两类是由3-或5-轮图经细分等构造出的,其星色数分别为2+2/(2n+1),2+3/(3n+1)和2+3/(3n-1).第三类平面图是由n-轮图经过Hajos构造得到的,其星色数为3+1/n.本类图的星色数结果推广了已有结论. 相似文献
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图的星色数的概念是Vince在1988年提出的,它是图的色数的一个推广.本文构造了一类星色数是4的平面图. 相似文献
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The purpose of this article is to offer new insight and tools toward the pursuit of the largest chromatic number in the class of thicknesstwo graphs. At present, the highest chromatic number known for a thickness‐two graph is 9, and there is only one known color‐critical such graph. We introduce 40 small 9‐critical thickness‐two graphs, and then use a newconstruction, the permuted layer graphs, together with a construction of Hajós to create an infinite family of 9‐critical thickness‐two graphs. Finally, a non‐trivial infinite subfamily of Catlin's graphs, with directly computable chromatic numbers, is shown to have thickness two. © 2007 Wiley Periodicals, Inc. J Graph Theory 57: 198–214, 2008 相似文献
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The concepts of (k, d)-coloring and the star chromatic number, studied by Vince, by Bondy and Hell, and by Zhu are shown to reflect the cographic instance of a wider concept, that of fractional nowhere-zero flows in regular matroids. © 1998 John Wiley & Sons, Inc. J. Graph Theory 28: 155–161, 1998 相似文献
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Carsten Thomassen 《Journal of Graph Theory》2006,52(3):257-265
We provide a new method for extending results on finite planar graphs to the infinite case. Thus a result of Ungar on finite graphs has the following extension: Every infinite, planar, cubic, cyclically 4‐edge‐connected graph has a representation in the plane such that every edge is a horizontal or vertical straight line segment, and such that no two edges cross. A result of Tamassia and Tollis extends as follows: Every countably infinite planar graph is a subgraph of a visibility graph. Furthermore, every locally finite, 2‐connected, planar graph is a visibility graph. © 2006 Wiley Periodicals, Inc. J Graph Theory 52: 257–265, 2006 相似文献
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We investigate the relation between the multichromatic number (discussed by Stahl and by Hilton, Rado and Scott) and the star chromatic number (introduced by Vince) of a graph. Denoting these by χ* and η*, the work of the above authors shows that χ*(G) = η*(G) if G is bipartite, an odd cycle or a complete graph. We show that χ*(G) ≤ η*(G) for any finite simple graph G. We consider the Kneser graphs , for which χ* = m/n and η*(G)/χ*(G) is unbounded above. We investigate particular classes of these graphs and show that η* = 3 and η* = 4; (n ≥ 1), and η* = m - 2; (m ≥ 4). © 1997 John Wiley & Sons, Inc. J Graph Theory 26: 137–145, 1997 相似文献
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This article studies the circular chromatic number of a class of circular partitionable graphs. We prove that an infinite family of circular partitionable graphs G has . A consequence of this result is that we obtain an infinite family of graphs G with the rare property that the deletion of each vertex decreases its circular chromatic number by exactly 1. © 2006 Wiley Periodicals, Inc. J Graph Theory 相似文献
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Xingxing Yu 《Journal of Graph Theory》2005,48(4):247-266
A graph is k‐indivisible, where k is a positive integer, if the deletion of any finite set of vertices results in at most k – 1 infinite components. In 1971, Nash‐Williams conjectured that a 4‐connected infinite planar graph contains a spanning 2‐way infinite path if and only if it is 3‐indivisible. In this paper, we prove a structural result for 2‐indivisible infinite planar graphs. This structural result is then used to prove Nash‐Williams conjecture for all 4‐connected 2‐indivisible infinite planar graphs. © 2005 Wiley Periodicals, Inc. J Graph Theory 48: 247–266, 2005 相似文献
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MacGillivary and Seyffarth [G. MacGillivray, K. Seyffarth, Domination numbers of planar graphs, J. Graph Theory 22 (1996) 213–229] proved that planar graphs of diameter two have domination number at most three. Goddard and Henning [W. Goddard, M.A. Henning, Domination in planar graphs with small diameter, J. Graph Theory 40 (2002) 1–25] showed that there is a unique planar graph of diameter two with domination number three. It follows that the total domination number of a planar graph of diameter two is at most three. In this paper, we consider the problem of characterizing planar graphs with diameter two and total domination number three. We say that a graph satisfies the domination-cycle property if there is some minimum dominating set of the graph not contained in any induced 5-cycle. We characterize the planar graphs with diameter two and total domination number three that satisfy the domination-cycle property and show that there are exactly thirty-four such planar graphs. 相似文献
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Chin‐Ann Soh 《Journal of Graph Theory》2007,55(1):14-26
The circular chromatic number is a refinement of the chromatic number of a graph. It has been established in [3,6,7] that there exists planar graphs with circular chromatic number r if and only if r is a rational in the set {1} ∪ [2,4]. Recently, Mohar, in [1,2] has extended the concept of the circular chromatic number to digraphs and it is interesting to ask what the corresponding result is for digraphs. In this article, we shall prove the new result that there exist planar digraphs with circular chromatic number r if and only if r is a rational in the interval [1,4]. © 2006 Wiley Periodicals, Inc. J Graph Theory 55: 14–26, 2007 相似文献
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We investigate vertex‐transitive graphs that admit planar embeddings having infinite faces, i.e., faces whose boundary is a double ray. In the case of graphs with connectivity exactly 2, we present examples wherein no face is finite. In particular, the planar embeddings of the Cartesian product of the r‐valent tree with K2 are comprehensively studied and enumerated, as are the automorphisms of the resulting maps, and it is shown for r = 3 that no vertex‐transitive group of graph automorphisms is extendable to a group of homeomorphisms of the plane. We present all known families of infinite, locally finite, vertex‐transitive graphs of connectivity 3 and an infinite family of 4‐connected graphs that admit planar embeddings wherein each vertex is incident with an infinite face. © 2003 Wiley Periodicals, Inc. J Graph Theory 42: 257–275, 2003 相似文献
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We prove that for any planar graph G with maximum degree Δ, it holds that the chromatic number of the square of G satisfies χ(G2) ≤ 2Δ + 25. We generalize this result to integer labelings of planar graphs involving constraints on distances one and two in the graph. © 2002 Wiley Periodicals, Inc. J Graph Theory 42: 110–124, 2003 相似文献
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1988年,Vince定义了图的色数的一个推广——图的星色数,本文研究了有围长限制或有最大度限制的临界图的星色数,得到了三个新结果。 相似文献
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This note proves that the game chromatic number of an outerplanar graph is at most 7. This improves the previous known upper bound of the game chromatic number of outerplanar graphs. © 1999 John Wiley & Sons, Inc. J Graph Theory 30: 67–70, 1999 相似文献
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Xingxing Yu 《Journal of Graph Theory》2006,53(3):173-195
Nash‐Williams conjectured that a 4‐connected infinite planar graph contains a spanning 2‐way infinite path if, and only if, the deletion of any finite set of vertices results in at most two infinite components. In this article, we prove this conjecture for graphs with no dividing cycles and for graphs with infinitely many vertex disjoint dividing cycles. A cycle in an infinite plane graph is called dividing if both regions of the plane bounded by this cycle contain infinitely many vertices of the graph. © 2006 Wiley Periodicals, Inc. J Graph Theory 53: 173–195, 2006 相似文献
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T. H. Marshall 《Journal of Graph Theory》2006,52(3):200-210
We prove that every oriented planar graph admits a homomorphism to the Paley tournament P271 and hence that every oriented planar graph has an antisymmetric flow number and a strong oriented chromatic number of at most 271. © 2006 Wiley Periodicals, Inc. J Graph Theory 52: 200–210, 2006 相似文献