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On the number of vertices with a given degree in a Galton-Watson tree

Published online by Cambridge University Press:  01 July 2016

Nariyuki Minami*
Affiliation:
University of Tsukuba
*
Postal address: Institute of Mathematics, University of Tsukuba, Tsukuba 305-8571, Japan. Email address: minami@math.tsukuba.ac.jp
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Abstract

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Let Yk(ω) (k ≥ 0) be the number of vertices of a Galton-Watson tree ω that have k children, so that Z(ω) := ∑k≥0Yk(ω) is the total progeny of ω. In this paper, we will prove various statistical properties of Z and Yk. We first show, under a mild condition, an asymptotic expansion of P(Z = n) as n → ∞, improving the theorem of Otter (1949). Next, we show that Yk(ω) := ∑j=0kYj(ω) is the total progeny of a new Galton-Watson tree that is hidden in the original tree ω. We then proceed to study the joint probability distribution of Z and Ykk, and show that, as n → ∞, Yk/nk is asymptotically Gaussian under the conditional distribution P(· | Z = n).

Type
General Applied Probability
Copyright
Copyright © Applied Probability Trust 2005 

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