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Longest paths in random Apollonian networks and largest r-ary subtrees of random d-ary recursive trees

Part of: Combinatorial probability Graph theory

Published online by Cambridge University Press:  24 October 2016

Andrea Collevecchio ,
Abbas Mehrabian  and
Nick Wormald
Andrea Collevecchio*
Affiliation:
Monash University
Abbas Mehrabian*
Affiliation:
University of Waterloo
Nick Wormald*
Affiliation:
Monash University
*
* Postal address: School of Mathematical Sciences, 9 Rainforest Walk, Clayton, VIC 3800, Australia.
*** Postal address: Department of Combinatorics and Optimization, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1 Canada. Email address: amehrabi@uwaterloo.ca
* Postal address: School of Mathematical Sciences, 9 Rainforest Walk, Clayton, VIC 3800, Australia.
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Abstract

Let r and d be positive integers with r<d. Consider a random d-ary tree constructed as follows. Start with a single vertex, and in each time-step choose a uniformly random leaf and give it d newly created offspring. Let 𝒯d,t be the tree produced after t steps. We show that there exists a fixed δ<1 depending on d and r such that almost surely for all large t, every r-ary subtree of 𝒯d,t has less than t δ vertices. The proof involves analysis that also yields a related result. Consider the following iterative construction of a random planar triangulation. Start with a triangle embedded in the plane. In each step, choose a bounded face uniformly at random, add a vertex inside that face and join it to the vertices of the face. In this way, one face is destroyed and three new faces are created. After t steps, we obtain a random triangulated plane graph with t+3 vertices, which is called a random Apollonian network. We prove that there exists a fixed δ<1, such that eventually every path in this graph has length less than t 𝛿, which verifies a conjecture of Cooper and Frieze (2015).

Keywords

Random Apollonian networkrandom d-ary recursive treelongest pathEggenberger–Pólya urn

MSC classification

Primary: 05C80: Random graphs
Secondary: 60C05: Combinatorial probability 05C05: Trees
Type
Research Papers
Information
Journal of Applied Probability , Volume 53 , Issue 3 , September 2016 , pp. 846 - 856
Copyright
Copyright © Applied Probability Trust 2016 

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