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Paper   IPM / Computer Science / 10946
School of Computer Science
  Title:   On the complexity of the circular chromatic number
  Author(s): 
1.  H. Hatami
2.  R. Tusserkani
  Status:   Published
  Journal: Journal of Graph Theory
  No.:  3
  Vol.:  47
  Year:  2004
  Publisher(s):   John Wiley & Sons
  Supported by:  IPM
  Abstract:
Circular chromatic number, ?c is a natural generalization of chromatic number. It is known that it is NP-hard to determine whether or not an arbitrary graph G satisfies ?(G)=?c(G). In this paper we prove that this problem is NP-hard even if the chromatic number of the graph is known. This answers a question of Xuding Zhu. Also we prove that for all positive integers k?=?2 and n?=?3, for a given graph G with ?(G)?=?n, it is NP-complete to verify if χc(G) ≤ n1/k. � 2004 Wiley Periodicals, Inc. J Graph Theory 47: 226�230, 2004

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