Jim Pitman

  1. Archimedes, Gauss, and Stein.

    Authors: Jim Pitman, Nathan Ross
    Subjects: Probability
    Abstract

    We discuss a characterization of the centered Gaussian distribution which can
    be read from results of Archimedes and Maxwell, and relate it to Charles
    Stein's well-known characterization of the same distribution. These
    characterizations fit into a more general framework involving the beta-gamma
    algebra, which explains some other characterizations appearing in the Stein's
    method literature.

  2. Beta processes, stick-breaking, and power laws.

    Authors: Michael I. Jordan, Jim Pitman, Tamara Broderick
    Subjects: Methodology
    Abstract

    The beta-Bernoulli process provides a Bayesian nonparametric prior for models
    involving collections of binary-valued features. A draw from the beta process
    provides an infinite collection of probabilities in the unit interval, and a
    draw from the Bernoulli process turns these into binary-valued features. Recent
    work has shown how to derive stick-breaking representations for the beta
    process, by analogy to Sethuraman's derivation of a stick-breaking
    representation for the Dirichlet process.

  3. Convex minorants of random walks and L\'evy processes.

    Authors: Jim Pitman, Gerónimo Uribe Bravo, Nathan Ross, Josh Abramson
    Subjects: Probability
    Abstract

    This article provides an overview of recent work on descriptions and
    properties of the convex minorant of random walks and L\'evy processes which
    summarize and extend the literature on these subjects.

  4. The greatest convex minorant of Brownian motion, meander, and bridge.

    Authors: Jim Pitman, Nathan Ross
    Subjects: Probability
    Abstract

    This article contains both a point process and a sequential description of
    the greatest convex minorant of Brownian motion on a finite interval. We use
    these descriptions to provide new analysis of various features of the convex
    minorant such as the set of times where the Brownian motion meets its minorant.
    The equivalence of the these descriptions is non-trivial, which leads to many
    interesting identities between quantities derived from our analysis. The
    sequential description can be viewed as a Markov chain for which we derive some
    fundamental properties.

  5. The convex minorant of a L\'evy process.

    Authors: Jim Pitman, Gerónimo Uribe Bravo
    Subjects: Probability
    Abstract

    We offer a unified approach to the theory of convex minorants of L\'evy
    processes with continuous distributions. New results include simple and
    explicit constructions of the convex minorant of a L\'evy process, on both
    finite and infinite time intervals, and of a Poisson point process of
    excursions above the convex minorant up to an independent exponential time. The
    Poisson-Dirichlet distribution of parameter 1 is shown to be the universal law
    of ranked lengths of excursions of a L\'evy process with continuous
    distributions above its convex minorant on the interval $[0,1]$.

  6. The distribution of the maximal difference between Brownian bridge and its concave majorant.

    Authors: Jim Pitman, Fadoua Balabdaoui
    Subjects: Statistics
    Abstract

    We provide a representation of the maximal difference between a standard
    Brownian bridge and its concave majorant on the unit interval, from which we
    deduce expressions for the distribution and density functions and moments of
    this difference. This maximal difference has an application in nonparametric
    statistics where it arises in testing monotonicity of a density or regression
    curve.

  7. The distribution of the maximal difference between Brownian bridge and its concave majorant.

    Authors: Jim Pitman, Fadoua Balabdaoui
    Subjects: Statistics
    Abstract

    We provide a representation of the maximal difference between a standard
    Brownian bridge and its concave majorant on the unit interval, from which we
    deduce expressions for the distribution and density functions and moments of
    this difference. This maximal difference has an application in nonparametric
    statistics where it arises in testing monotonicity of a density or regression
    curve.

  8. Regenerative tree growth: Binary self-similar continuum random trees and Poisson--Dirichlet compositions.

    Authors: Jim Pitman, Matthias Winkel
    Subjects: Probability
    Abstract

    We use a natural ordered extension of the Chinese Restaurant Process to grow
    a two-parameter family of binary self-similar continuum fragmentation trees. We
    provide an explicit embedding of Ford's sequence of alpha model trees in the
    continuum tree which we identified in a previous article as a distributional
    scaling limit of Ford's trees. In general, the Markov branching trees induced
    by the two-parameter growth rule are not sampling consistent, so the existence
    of compact limiting trees cannot be deduced from previous work on the sampling
    consistent case.

  9. Characterizations of exchangeable partitions and random discrete distributions by deletion properties.

    Authors: Jim Pitman, Alexander Gnedin, Chris Haulk
    Subjects: Probability
    Abstract

    We prove a long-standing conjecture which characterises the Ewens-Pitman
    two-parameter family of exchangeable random partitions, plus a short list of
    limit and exceptional cases, by the following property: for each $n = 2,3,
    >...$, if one of $n$ individuals is chosen uniformly at random, independently
    of the random partition $\pi_n$ of these individuals into various types, and
    all individuals of the same type as the chosen individual are deleted, then for
    each $r > 0$, given that $r$ individuals remain, these individuals are
    partitioned according to $\pi_r'$ for some sequence of rando

  10. Spinal partitions and invariance under re-rooting of continuum random trees.

    Authors: Bénédicte Haas, Jim Pitman, Matthias Winkel
    Subjects: Probability
    Abstract

    We develop some theory of spinal decompositions of discrete and continuous
    fragmentation trees. Specifically, we consider a coarse and a fine spinal
    integer partition derived from spinal tree decompositions. We prove that for a
    two-parameter Poisson--Dirichlet family of continuous fragmentation trees,
    including the stable trees of Duquesne and Le Gall, the fine partition is
    obtained from the coarse one by shattering each of its parts independently,
    according to the same law.

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