New upper bounds on feedback vertex numbers in butterflies

  • Authors:
  • Maw-Shang Chang;Chin-Hua Lin;Chuan-Min Lee

  • Affiliations:
  • Department of Computer Science and Information Engineering, National Chung Cheng University, Ming-Hsiung, Chiayi 621, Taiwan, ROC;Department of Computer Science and Information Engineering, National Chung Cheng University, Ming-Hsiung, Chiayi 621, Taiwan, ROC;Department of Computer Science and Information Engineering, National Chung Cheng University, Ming-Hsiung, Chiayi 621, Taiwan, ROC

  • Venue:
  • Information Processing Letters
  • Year:
  • 2004

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Abstract

Butterflies are undirected graphs of bounded degree. They are widely used as interconnection networks. In this paper we study the feedback vertex set problem for butterflies. We show that the feedback vertex set found by Luccio's algorithm [Inform. Process. Lett. 66 (1998) 59-64] for the k-dimensional butterfly Bk is of size ⌊(3k + 1)2k + 1/9⌋. Besides, we propose an algorithm to find a feedback vertex set of size either ⌊(3k + 1)2k + 1/9⌋ - 2k - 1/3 or ⌊(3k + 1)2k + 1/9⌋ - 2k - 2 ⌈k/2⌉ - 2⌊k/2⌋ + 1 / 3 for Bk depending on whether k is even or odd.