Asymptotic variance of random symmetric digital search trees
Authors: Hsien-Kuei Hwang 1; Michael Fuchs 2; Vytas Zacharovas 1
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Hsien-Kuei Hwang;Michael Fuchs;Vytas Zacharovas
1 Institute of Statistical Science
2 Department of Applied Mathematics [Hsinchu]
Asymptotics of the variances of many cost measures in random digital search trees are often notoriously messy and involved to obtain. A new approach is proposed to facilitate such an analysis for several shape parameters on random symmetric digital search trees. Our approach starts from a more careful normalization at the level of Poisson generating functions, which then provides an asymptotically equivalent approximation to the variance in question. Several new ingredients are also introduced such as a combined use of the Laplace and Mellin transforms and a simple, mechanical technique for justifying the analytic de-Poissonization procedures involved. The methodology we develop can be easily adapted to many other problems with an underlying binomial distribution. In particular, the less expected and somewhat surprising n (logn)(2)-variance for certain notions of total path-length is also clarified.