Mostrando recursos 1 - 20 de 39

  1. Stability of queueing networks

    Bramson, Maury

  2. The notion of ψ-weak dependence and its applications to bootstrapping time series

    Doukhan, Paul; Neumann, Michael H.
    We give an introduction to a notion of weak dependence which is more general than mixing and allows to treat for example processes driven by discrete innovations as they appear with time series bootstrap. As a typical example, we analyze autoregressive processes and their bootstrap analogues in detail and show how weak dependence can be easily derived from a contraction property of the process. Furthermore, we provide an overview of classes of processes possessing the property of weak dependence and describe important probabilistic results under such an assumption.

  3. Differential equation approximations for Markov chains

    Darling, R.W.R.; Norris, J.R.
    We formulate some simple conditions under which a Markov chain may be approximated by the solution to a differential equation, with quantifiable error probabilities. The role of a choice of coordinate functions for the Markov chain is emphasised. The general theory is illustrated in three examples: the classical stochastic epidemic, a population process model with fast and slow variables, and core-finding algorithms for large random hypergraphs.

  4. Branching diffusions, superdiffusions and random media

    Engländer, János
    Spatial branching processes became increasingly popular in the past decades, not only because of their obvious connection to biology, but also because superprocesses are intimately related to nonlinear partial differential equations. Another hot topic in today’s research in probability theory is ‘random media’, including the now classical problems on ‘Brownian motion among obstacles’ and the more recent ‘random walks in random environment’ and ‘catalytic branching’ models. These notes aim to give a gentle introduction into some topics in spatial branching processes and superprocesses in deterministic environments (sections 2-6) and in random media (sections 7-11).

  5. Proofs of the martingale FCLT

    Whitt, Ward
    This is an expository review paper elaborating on the proof of the martingale functional central limit theorem (FCLT). This paper also reviews tightness and stochastic boundedness, highlighting one-dimensional criteria for tightness used in the proof of the martingale FCLT. This paper supplements the expository review paper Pang, Talreja and Whitt (2007) illustrating the “martingale method” for proving many-server heavy-traffic stochastic-process limits for queueing models, supporting diffusion-process approximations.

  6. Martingale proofs of many-server heavy-traffic limits for Markovian queues

    Pang, Guodong; Talreja, Rishi; Whitt, Ward
    This is an expository review paper illustrating the “martingale method” for proving many-server heavy-traffic stochastic-process limits for queueing models, supporting diffusion-process approximations. Careful treatment is given to an elementary model – the classical infinite-server model M/M/∞, but models with finitely many servers and customer abandonment are also treated. The Markovian stochastic process representing the number of customers in the system is constructed in terms of rate-1 Poisson processes in two ways: (i) through random time changes and (ii) through random thinnings. Associated martingale representations are obtained for these constructions by applying, respectively: (i) optional stopping theorems where the random time...

  7. Pseudo-maximization and self-normalized processes

    de la Peña, Victor H.; Klass, Michael J.; Lai, Tze Leung
    Self-normalized processes are basic to many probabilistic and statistical studies. They arise naturally in the the study of stochastic integrals, martingale inequalities and limit theorems, likelihood-based methods in hypothesis testing and parameter estimation, and Studentized pivots and bootstrap-t methods for confidence intervals. In contrast to standard normalization, large values of the observations play a lesser role as they appear both in the numerator and its self-normalized denominator, thereby making the process scale invariant and contributing to its robustness. Herein we survey a number of results for self-normalized processes in the case of dependent variables and describe a key method called...

  8. Notes on the occupancy problem with infinitely many boxes: general asymptotics and power laws

    Gnedin, Alexander; Hansen, Ben; Pitman, Jim
    This paper collects facts about the number of occupied boxes in the classical balls-in-boxes occupancy scheme with infinitely many positive frequencies: equivalently, about the number of species represented in samples from populations with infinitely many species. We present moments of this random variable, discuss asymptotic relations among them and with related random variables, and draw connections with regular variation, which appears in various manifestations.

  9. Brownian excursion area, Wright’s constants in graph enumeration, and other Brownian areas

    Janson, Svante
    This survey is a collection of various results and formulas by different authors on the areas (integrals) of five related processes, viz. Brownian motion, bridge, excursion, meander and double meander; for the Brownian motion and bridge, which take both positive and negative values, we consider both the integral of the absolute value and the integral of the positive (or negative) part. This gives us seven related positive random variables, for which we study, in particular, formulas for moments and Laplace transforms; we also give (in many cases) series representations and asymptotics for density functions and distribution functions. We further study...

  10. A survey of random processes with reinforcement

    Pemantle, Robin
    The models surveyed include generalized Pólya urns, reinforced random walks, interacting urn models, and continuous reinforced processes. Emphasis is on methods and results, with sketches provided of some proofs. Applications are discussed in statistics, biology, economics and a number of other areas.

  11. On the constructions of the skew Brownian motion

    Lejay, Antoine
    This article summarizes the various ways one may use to construct the Skew Brownian motion, and shows their connections. Recent applications of this process in modelling and numerical simulation motivates this survey. This article ends with a brief account of related results, extensions and applications of the Skew Brownian motion.

  12. An essay on the general theory of stochastic processes

    Nikeghbali, Ashkan
    This text is a survey of the general theory of stochastic processes, with a view towards random times and enlargements of filtrations. The first five chapters present standard materials, which were developed by the French probability school and which are usually written in French. The material presented in the last three chapters is less standard and takes into account some recent developments.

  13. Uniqueness and non-uniqueness in percolation theory

    Häggström, Olle; Jonasson, Johan
    This paper is an up-to-date introduction to the problem of uniqueness versus non-uniqueness of infinite clusters for percolation on ℤd and, more generally, on transitive graphs. For iid percolation on ℤd, uniqueness of the infinite cluster is a classical result, while on certain other transitive graphs uniqueness may fail. Key properties of the graphs in this context turn out to be amenability and nonamenability. The same problem is considered for certain dependent percolation models – most prominently the Fortuin–Kasteleyn random-cluster model – and in situations where the standard connectivity notion is replaced by entanglement or rigidity. So-called simultaneous uniqueness in...

  14. Level crossings and other level functionals of stationary Gaussian processes

    Kratz, Marie F.
    This paper presents a synthesis on the mathematical work done on level crossings of stationary Gaussian processes, with some extensions. The main results [(factorial) moments, representation into the Wiener Chaos, asymptotic results, rate of convergence, local time and number of crossings] are described, as well as the different approaches [normal comparison method, Rice method, Stein-Chen method, a general m-dependent method] used to obtain them; these methods are also very useful in the general context of Gaussian fields. Finally some extensions [time occupation functionals, number of maxima in an interval, process indexed by a bidimensional set] are proposed, illustrating the generality...

  15. Determinantal Processes and Independence

    Hough, J. Ben; Krishnapur, Manjunath; Peres, Yuval; Virág, Bálint
    We give a probabilistic introduction to determinantal and permanental point processes. Determinantal processes arise in physics (fermions, eigenvalues of random matrices) and in combinatorics (nonintersecting paths, random spanning trees). They have the striking property that the number of points in a region D is a sum of independent Bernoulli random variables, with parameters which are eigenvalues of the relevant operator on L2(D). Moreover, any determinantal process can be represented as a mixture of determinantal projection processes. We give a simple explanation for these known facts, and establish analogous representations for permanental processes, with geometric variables replacing the Bernoulli variables. These...

  16. The realization of positive random variables via absolutely continuous transformations of measure on Wiener space

    Feyel, D.; Üstünel, A. S.; Zakai, M.
    Let μ be a Gaussian measure on some measurable space {W={w},ℬ(W)} and let ν be a measure on the same space which is absolutely continuous with respect to ν. The paper surveys results on the problem of constructing a transformation T on the W space such that Tw=w+u(w) where u takes values in the Cameron-Martin space and the image of μ under T is μ. In addition we ask for the existence of transformations T belonging to some particular classes.

  17. Localization and delocalization of random interfaces

    Velenik, Yvan
    The probabilistic study of effective interface models has been quite active in recent years, with a particular emphasis on the effect of various external potentials (wall, pinning potential, ...) leading to localization/delocalization transitions. I review some of the results that have been obtained. In particular, I discuss pinning by a local potential, entropic repulsion and the (pre)wetting transition, both for models with continuous and discrete heights.

  18. Markov chain comparison

    Dyer, Martin; Goldberg, Leslie Ann; Jerrum, Mark; Martin, Russell
    This is an expository paper, focussing on the following scenario. We have two Markov chains, ℳ and ℳ'. By some means, we have obtained a bound on the mixing time of ℳ'. We wish to compare ℳ with ℳ' in order to derive a corresponding bound on the mixing time of ℳ. We investigate the application of the comparison method of Diaconis and Saloff-Coste to this scenario, giving a number of theorems which characterize the applicability of the method. We focus particularly on the case in which the chains are not reversible. The purpose of the paper is to provide...

  19. The geometry of Brownian surfaces

    Léandre, Rémi
    Motivated by Segal’s axiom of conformal field theory, we do a survey on geometrical random fields. We do a history of continuous random fields in order to arrive at a field theoretical analog of Klauder’s quantization in Hamiltonian quantum mechanic by using infinite dimensional Airault-Malliavin Brownian motion.

  20. Recent advances in invariance principles for stationary sequences

    Merlevède, Florence; Peligrad, Magda; Utev, Sergey
    In this paper we survey some recent results on the central limit theorem and its weak invariance principle for stationary sequences. We also describe several maximal inequalities that are the main tool for obtaining the invariance principles, and also they have interest in themselves. The classes of dependent random variables considered will be martingale-like sequences, mixing sequences, linear processes, additive functionals of ergodic Markov chains.

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