Analytical depoissonization and its applications

  • Authors:
  • Philippe Jacquet;Wojciech Szpankowski

  • Affiliations:
  • INRIA, Le Chesnay, France;Purdue Univ., West Lafayette, IN

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 1998

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Abstract

In combinatorics and analysis of algorithms a Poisson version of aproblem (henceforth called a Poissonmodel orpoissonization) is often easier tosolve than the original one, which we name here theBernoulli model. Poissonization is atechnique that replaces the original input (e.g., think of balls throwninto urns) by a Poisson process (e.g., think of balls arriving accordingto a Poisson process into urns). More precisely, analytical Poissontransform maps a sequence (e.g., characterizing the Bernoulli model)into a generating function of a complex variable. However, afterpoissonization one must depoissonizein order to translate the results of the Poisson model into theoriginal (i.e., Bernoulli) model. We present in this paper severalanalytical depoissonization results that fall into the following generalscheme: If the Poisson transform has an appropriategrowth in the complex plane, then an asymptotic expansion of thesequence can be expressed in terms of the Poisson transform and itsderivatives evaluated on the real line. Notsurprisingly, actual formulations of depoissonization results depend onthe nature of the growth of the Poisson transform, and thus we havepolynomial andexponential depoissonizationtheorems. Normalization (e.g., as in the central limit theorem)introduces another twist that led us to formulate the so-calleddiagonal depoissonization theorems.Finally, we illustrate our results on numerous examples fromcombinatorics and the analysis of algorithms and data structures (e.g.,combinatorial assemblies, digital trees, multiaccess protocols,probabilistic counting, selecting a leader, data compression,etc.).—Authors' Abstract