The double CFTP method

  • Authors:
  • Luc Devroye;Lancelot F. James

  • Affiliations:
  • McGill University, Montreal, Canada;Hong Kong University of Science and Technology, Kowloon, Hong Kong

  • Venue:
  • ACM Transactions on Modeling and Computer Simulation (TOMACS)
  • Year:
  • 2011

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Abstract

We consider the problem of the exact simulation of random variables Z that satisfy the distributional identity Z =L VY + (1-V)Z, where V ∈ [0,1] and Y are independent, and =L denotes equality in distribution. Equivalently, Z is the limit of a Markov chain driven by that map. We give an algorithm that can be automated under the condition that we have a source capable of generating independent copies of Y, and that V has a density that can be evaluated in a black-box format. The method uses a doubling trick for inducing coalescence in coupling from the past. Applications include exact samplers for many Dirichlet means, some two-parameter Poisson--Dirichlet means, and a host of other distributions related to occupation times of Bessel bridges that can be described by stochastic fixed point equations.