On mean distance and girth

  • Authors:
  • Siham Bekkai;Mekkia Kouider

  • Affiliations:
  • LAID3, U.S.T.H.B, Faculté de Mathématiques, BP.32 El-Alia, Bab Ezzouar, 16111 Alger, Algérie;LRI, Université Paris-Sud, UMR 8623, Bít. 490,91405 Orsay Cedex, France

  • Venue:
  • Discrete Applied Mathematics
  • Year:
  • 2010

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Abstract

We bound the mean distance in a connected graph which is not a tree in terms of its order n and its girth g. On one hand, we show that the mean distance is at most n+13-g(g^2-4)12n(n-1)-g(g-2)(n-g)2n(n-1) if g is even and at most n+13-g(g^2-1)12n(n-1)-(g-1)^2(n-g)2n(n-1) if g is odd. On the other hand, we prove that the mean distance is at least ng4(n-1) unless G is an odd cycle. This resolves two conjectures of AutoGraphiX.