THE ANNALS of PROBABILITY
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Brownian Motion and the Heat Equation
Brownian motion and the heat equation Denis Bell University of North Florida 1. The heat equation Let the function u(t, x) denote the temperature in a rod at position x and time t u(t,x) Then u(t, x) satisfies the heat equation ∂u 1∂2u = , t > 0. (1) ∂t 2∂x2 It is easy to check that the Gaussian function 1 x2 u(t, x) = e−2t 2πt satisfies (1). Let φ be any! bounded continuous function and define 1 (x y)2 u(t, x) = ∞ φ(y)e− 2−t dy. 2πt "−∞ Then u satisfies!(1). Furthermore making the substitution z = (x y)/√t in the integral gives − 1 z2 u(t, x) = ∞ φ(x y√t)e−2 dz − 2π "−∞ ! 1 z2 φ(x) ∞ e−2 dz = φ(x) → 2π "−∞ ! as t 0. Thus ↓ 1 (x y)2 u(t, x) = ∞ φ(y)e− 2−t dy. 2πt "−∞ ! = E[φ(Xt)] where Xt is a N(x, t) random variable solves the heat equation ∂u 1∂2u = ∂t 2∂x2 with initial condition u(0, ) = φ. · Note: The function u(t, x) is smooth in x for t > 0 even if is only continuous. 2. Brownian motion In the nineteenth century, the botanist Robert Brown observed that a pollen particle suspended in liquid undergoes a strange erratic motion (caused by bombardment by molecules of the liquid) Letting w(t) denote the position of the particle in a fixed direction, the paths w typically look like this t N. Wiener constructed a rigorous mathemati- cal model of Brownian motion in the 1930s. -
Quasi Regular Dirichlet Forms and the Stochastic Quantization Problem
Quasi regular Dirichlet forms and the stochastic quantization problem Sergio Albeverio ∗† Zhi Ming Ma ‡ Michael R¨ockner †§ Dedicated to Masatoshi Fukushima for his 80th birthday 7.4.14 Abstract After recalling basic features of the theory of symmetric quasi regu- lar Dirichlet forms we show how by applying it to the stochastic quan- tization equation, with Gaussian space-time noise, one obtains weak solutions in a large invariant set. Subsequently, we discuss non sym- metric quasi regular Dirichlet forms and show in particular by two simple examples in infinite dimensions that infinitesimal invariance, does not imply global invariance. We also present a simple example of non-Markov uniqueness in infinite dimensions. 1 Introduction The theory of symmetric Dirichlet forms is the natural extension to higher dimensional state spaces of the classical Feller theory of stochastic processes on the real line. Through ground breaking work by Beurling and Deny (1958- 59), [BD58], [BD59], [Den70], [Sil74], [Sil76], and Fukushima (since 1971), [Fu71a], [Fu71b], [Fu80], [FOT11], [CF12], it has developed into a powerful method of combining analytic and functional analytic, as well as poten- tial theoretic and probabilistic methods to handle the basic construction of stochastic processes under natural conditions about the local characteris- arXiv:1404.2757v2 [math.PR] 30 Apr 2014 tics (e.g., drift and diffusion coefficients), avoiding unnecessary regularity conditions. Such processes arise in a number of applied problems where coefficients can be singular, locally or at infinity. For detailed expositions of the gen- eral theory, mainly concentrated on finite dimensional state spaces, see ∗Inst. Appl. Mathematics and HCM, University of Bonn; CERFIM (Locarno); [email protected] †BiBoS (Bielefeld, Bonn) ‡Inst. -
1 Introduction Branching Mechanism in a Superprocess from a Branching
数理解析研究所講究録 1157 巻 2000 年 1-16 1 An example of random snakes by Le Gall and its applications 渡辺信三 Shinzo Watanabe, Kyoto University 1 Introduction The notion of random snakes has been introduced by Le Gall ([Le 1], [Le 2]) to construct a class of measure-valued branching processes, called superprocesses or continuous state branching processes ([Da], [Dy]). A main idea is to produce the branching mechanism in a superprocess from a branching tree embedded in excur- sions at each different level of a Brownian sample path. There is no clear notion of particles in a superprocess; it is something like a cloud or mist. Nevertheless, a random snake could provide us with a clear picture of historical or genealogical developments of”particles” in a superprocess. ” : In this note, we give a sample pathwise construction of a random snake in the case when the underlying Markov process is a Markov chain on a tree. A simplest case has been discussed in [War 1] and [Wat 2]. The construction can be reduced to this case locally and we need to consider a recurrence family of stochastic differential equations for reflecting Brownian motions with sticky boundaries. A special case has been already discussed by J. Warren [War 2] with an application to a coalescing stochastic flow of piece-wise linear transformations in connection with a non-white or non-Gaussian predictable noise in the sense of B. Tsirelson. 2 Brownian snakes Throughout this section, let $\xi=\{\xi(t), P_{x}\}$ be a Hunt Markov process on a locally compact separable metric space $S$ endowed with a metric $d_{S}(\cdot, *)$ . -
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i PREFACE Teaching stochastic processes to students whose primary interests are in applications has long been a problem. On one hand, the subject can quickly become highly technical and if mathe- matical concerns are allowed to dominate there may be no time available for exploring the many interesting areas of applications. On the other hand, the treatment of stochastic calculus in a cavalier fashion leaves the student with a feeling of great uncertainty when it comes to exploring new material. Moreover, the problem has become more acute as the power of the dierential equation point of view has become more widely appreciated. In these notes, an attempt is made to resolve this dilemma with the needs of those interested in building models and designing al- gorithms for estimation and control in mind. The approach is to start with Poisson counters and to identity the Wiener process with a certain limiting form. We do not attempt to dene the Wiener process per se. Instead, everything is done in terms of limits of jump processes. The Poisson counter and dierential equations whose right-hand sides include the dierential of Poisson counters are developed rst. This leads to the construction of a sample path representa- tions of a continuous time jump process using Poisson counters. This point of view leads to an ecient problem solving technique and permits a unied treatment of time varying and nonlinear problems. More importantly, it provides sound intuition for stochastic dierential equations and their uses without allowing the technicalities to dominate. In treating estimation theory, the conditional density equation is given a central role. -
Sergio Albeverio
Sergio Albeverio Academic career 1966 Dr. rer. nat., ETH Zurich,¨ Switzerland (supervi- sor: R. Jost, M. Fierz) 1962 - 1971 Assistant Professor, Lecturer, Research Fel- low: ETH Zurich¨ (Switzerland), Imperial Colle- ge London (England, UK), Princeton University (NJ, USA) 1972 - 1977 Professor (Marseille, Oslo, and Naples) 1977 - 1979 Professor (H3), University of Bielefeld 1979 - 1997 Professor (H4), University of Bochum 1997 - 2008 Professor (H4/C4), University of Bonn 1997 - 2009 Professor and Director of Mathematics Sect., Accademia di Achitettura, USI, Mendrisio, Swit- zerland Since 2008 Professor Emeritus Longer research stays and invited professor- ships at many universities and research cen- ters in Europe, China, Japan, Mexico, Rus- sia/USSR, Saudi Arabia, USA Honours 1969 - 1971 SNF Research Awards 1993 Max Planck Research Award Since 2002 Listed in the ISI Highly Cited Scientists 2002 Doctor honoris causa, Oslo University, Norway (Bicentennial of N. H. Abel) 2002 Visiting Professorship (over several years) per chiara fama, University of Trento 2003 Bonn University Prize for an interdisciplinary project “Extreme events in natural and artificial systems” 2011 - 2015 Chair Professorship in Mathematics, King Fahd University of Petroleum and Mi- nerals (KFUPM) Offers 1988 Chair of Mathematics, per chiara fama, Roma University II, Italy Invited Lectures Plenary lecturer at over 230 international meetings, including: 1977 International Congress on Mathematical Physics, Rome, Italy 1983 International Congress on Mathematical Physics, Boulder, CO, USA 1986 International Congress on Mathematical Physics, Marseille, France 1988 International Congress on Mathematical Physics, Swansea, Wales, UK 1994 N. Wiener Memorial Symposium, East Lansing, MI, USA 1995 S. Lefshetz Memorial Lecture, UNAM, Mex. Soc. Math./AMS, Mexico City 2000 Conference in Honor of S. -
Levy Processes
LÉVY PROCESSES, STABLE PROCESSES, AND SUBORDINATORS STEVEN P.LALLEY 1. DEFINITIONSAND EXAMPLES d Definition 1.1. A continuous–time process Xt = X(t ) t 0 with values in R (or, more generally, in an abelian topological groupG ) isf called a Lévyg ≥ process if (1) its sample paths are right-continuous and have left limits at every time point t , and (2) it has stationary, independent increments, that is: (a) For all 0 = t0 < t1 < < tk , the increments X(ti ) X(ti 1) are independent. − (b) For all 0 s t the··· random variables X(t ) X−(s ) and X(t s ) X(0) have the same distribution.≤ ≤ − − − The default initial condition is X0 = 0. A subordinator is a real-valued Lévy process with nondecreasing sample paths. A stable process is a real-valued Lévy process Xt t 0 with ≥ initial value X0 = 0 that satisfies the self-similarity property f g 1/α (1.1) Xt =t =D X1 t > 0. 8 The parameter α is called the exponent of the process. Example 1.1. The most fundamental Lévy processes are the Wiener process and the Poisson process. The Poisson process is a subordinator, but is not stable; the Wiener process is stable, with exponent α = 2. Any linear combination of independent Lévy processes is again a Lévy process, so, for instance, if the Wiener process Wt and the Poisson process Nt are independent then Wt Nt is a Lévy process. More important, linear combinations of independent Poisson− processes are Lévy processes: these are special cases of what are called compound Poisson processes: see sec. -
A Guide to Brownian Motion and Related Stochastic Processes
Vol. 0 (0000) A guide to Brownian motion and related stochastic processes Jim Pitman and Marc Yor Dept. Statistics, University of California, 367 Evans Hall # 3860, Berkeley, CA 94720-3860, USA e-mail: [email protected] Abstract: This is a guide to the mathematical theory of Brownian mo- tion and related stochastic processes, with indications of how this theory is related to other branches of mathematics, most notably the classical the- ory of partial differential equations associated with the Laplace and heat operators, and various generalizations thereof. As a typical reader, we have in mind a student, familiar with the basic concepts of probability based on measure theory, at the level of the graduate texts of Billingsley [43] and Durrett [106], and who wants a broader perspective on the theory of Brow- nian motion and related stochastic processes than can be found in these texts. Keywords and phrases: Markov process, random walk, martingale, Gaus- sian process, L´evy process, diffusion. AMS 2000 subject classifications: Primary 60J65. Contents 1 Introduction................................. 3 1.1 History ................................ 3 1.2 Definitions............................... 4 2 BM as a limit of random walks . 5 3 BMasaGaussianprocess......................... 7 3.1 Elementarytransformations . 8 3.2 Quadratic variation . 8 3.3 Paley-Wiener integrals . 8 3.4 Brownianbridges........................... 10 3.5 FinestructureofBrownianpaths . 10 arXiv:1802.09679v1 [math.PR] 27 Feb 2018 3.6 Generalizations . 10 3.6.1 FractionalBM ........................ 10 3.6.2 L´evy’s BM . 11 3.6.3 Browniansheets ....................... 11 3.7 References............................... 11 4 BMasaMarkovprocess.......................... 12 4.1 Markovprocessesandtheirsemigroups. 12 4.2 ThestrongMarkovproperty. 14 4.3 Generators ............................. -
Stochastic Processes and Brownian Motion X(T) (Or X ) Is a Random Variable for Each Time T and • T Is Usually Called the State of the Process at Time T
Stochastic Processes A stochastic process • X = X(t) { } is a time series of random variables. Stochastic Processes and Brownian Motion X(t) (or X ) is a random variable for each time t and • t is usually called the state of the process at time t. A realization of X is called a sample path. • A sample path defines an ordinary function of t. • c 2006 Prof. Yuh-Dauh Lyuu, National Taiwan University Page 396 c 2006 Prof. Yuh-Dauh Lyuu, National Taiwan University Page 398 Stochastic Processes (concluded) Of all the intellectual hurdles which the human mind If the times t form a countable set, X is called a • has confronted and has overcome in the last discrete-time stochastic process or a time series. fifteen hundred years, the one which seems to me In this case, subscripts rather than parentheses are to have been the most amazing in character and • usually employed, as in the most stupendous in the scope of its consequences is the one relating to X = X . { n } the problem of motion. If the times form a continuum, X is called a — Herbert Butterfield (1900–1979) • continuous-time stochastic process. c 2006 Prof. Yuh-Dauh Lyuu, National Taiwan University Page 397 c 2006 Prof. Yuh-Dauh Lyuu, National Taiwan University Page 399 Random Walks The binomial model is a random walk in disguise. • Random Walk with Drift Consider a particle on the integer line, 0, 1, 2,... • ± ± Xn = µ + Xn−1 + ξn. In each time step, it can make one move to the right • with probability p or one move to the left with ξn are independent and identically distributed with zero • probability 1 p. -
Cognitive Network Management and Control with Significantly Reduced
Cognitive Network Management and Control with Significantly Reduced State Sensing Arman Rezaee, Student Member, Vincent W.S. Chan, Life Fellow IEEE, Fellow OSA Claude E. Shannon Communication and Network Group, RLE Massachusetts Institute of Technology, Cambridge MA, USA Emails: armanr, chan @mit.edu f g Abstract—Future networks have to accommodate an increase should be used to connect different origin-destination (OD) of 3-4 orders of magnitude in data rates with very heterogeneous pairs. In practice, various shortest path algorithms (Bellman- session sizes and sometimes with strict time deadline require- Ford, Dijkstra, etc.) are used to identify the optimal shortest ments. The dynamic nature of scheduling of large transactions and the need for rapid actions by the Network Management path. The correctness of these algorithms requires the assump- and Control (NMC) system, require timely collection of network tion that after some period of time the system will settle state information. Rough estimates of the size of detailed net- into its steady state. We refer interested readers to [4] for a work states suggest large volumes of data with refresh rates thorough explanation of these issues. With the dynamic nature commensurate with the coherence time of the states (can be of current and future networks, the steady state assumption is as fast as 100 ms), resulting in huge burden and cost for the network transport (∼300 Gbps/link) and computation resources. particularly not valid, nonetheless the basic functional unit of Thus, judicious sampling of network states is necessary for these algorithms can be adapted to address the new challenges. a cost-effective network management system. -
Continuous Dependence on the Coefficients for Mean-Field Fractional Stochastic Delay Evolution Equations
Journal of Stochastic Analysis Volume 1 Number 3 Article 2 August 2020 Continuous Dependence on the Coefficients for Mean-Field Fractional Stochastic Delay Evolution Equations Brahim Boufoussi Cadi Ayyad University, Marrakesh, Morocco, [email protected] Salah Hajji Regional Center for the Professions of Education and Training, Marrakesh, Morocco, [email protected] Follow this and additional works at: https://digitalcommons.lsu.edu/josa Part of the Analysis Commons, and the Other Mathematics Commons Recommended Citation Boufoussi, Brahim and Hajji, Salah (2020) "Continuous Dependence on the Coefficients for Mean-Field Fractional Stochastic Delay Evolution Equations," Journal of Stochastic Analysis: Vol. 1 : No. 3 , Article 2. DOI: 10.31390/josa.1.3.02 Available at: https://digitalcommons.lsu.edu/josa/vol1/iss3/2 Journal of Stochastic Analysis Vol. 1, No. 3 (2020) Article 2 (14 pages) digitalcommons.lsu.edu/josa DOI: 10.31390/josa.1.3.02 CONTINUOUS DEPENDENCE ON THE COEFFICIENTS FOR MEAN-FIELD FRACTIONAL STOCHASTIC DELAY EVOLUTION EQUATIONS BRAHIM BOUFOUSSI AND SALAH HAJJI* Abstract. We prove that the mild solution of a mean-field stochastic func- tional differential equation, driven by a fractional Brownian motion in a Hilbert space, is continuous in a suitable topology, with respect to the initial datum and all coefficients. 1. Introduction In this paper we are concerned by the following stochastic delay differential equation of McKean-Vlasov type: dx(t)=(Ax(t)+f(t, x ,P ))dt + g(t)dBH (t),t [0,T] t x(t) (1.1) x(t)=ϕ(t),t [ r, 0], ∈ ∈ − where A is the infinitesimal generator of a strongly continuous semigroup of bounded linear operators, (S(t))t 0, in a Hilbert space X,thedrivingprocess H ≥ B is a fractional Brownian motion with Hurst parameter H (1/2, 1), Px(t) is the probability distribution of x(t), x ([ r, 0],X) is the function∈ defined by t ∈C − xt(s)=x(t + s) for all s [ r, 0], and f :[0, + ) ([ r, 0],X) 2(X) 0 ∈ − ∞ ×C − ×P → X, g :[0, + ) 2(Y,X) are appropriate functions. -
1 Introduction 2 White Noise
1 Introduction The content of these notes is also covered by chapter 4 section A of [1]. 2 White noise In applications infinitesimal Wiener increments are represented as dwt = ηt dt The stochastic process ηt is referred to as white noise. Consistence of the definition requires ηt to be a Gaussian process with the following properties. • Zero average: ≺ ηt = 0 Namely we must have 0 =≺ wt+dt − wt =≺ ηt dt • δ-correlation: at any instant of time 2 (1) 2 ≺ ηtηs = σ δ (t − s) ; σ > 0 as it follows from the identification d d ≺ w w =≺ η η (2.1) dt ds t s t s Namely, writing the correlation of the Wiener process in terms of the Heaviside step function 2 ≺ wtws = σ [s H(t − s) + t H(s − t)] (2.2) and observing d H(t − s) = δ(1)(t − s) dt we obtain, upon inserting (2.2) into (2.1) d d d d ≺ w w = σ2 [H(t − s) − s δ(1)(t − s)] + σ2 [H(s − t) − t δ(1)(s − t)] dt ds t s dt ds By construction the δ is even an even function of its argument: the right hand side can be couched into the form d d d ≺ w w = σ2 2 δ(1)(t − s) + (t − s) δ(1)(t − s) dt ds t s dt In order to interpret the meaning of the derivative, we integrate the right hand side over a smooth test function f Z s+" d dt f(t)(t − s) δ(1)(t − s) s−" dt Z σ+" df Z σ+" = − dt (t)(t − s) δ(1)(t − s) − dt f(t) δ(1)(t − s) s−" dt s−" Z σ+" = − dt f(t) δ(1)(t − s) = −f(s) (2.3) s−" 1 We conclude that d d ≺ w w = σ2δ(1)(t − s) dt ds t s the identity determining the value of the white noise correlation. -
Nontrivial Attractors in a Model Related to the Three-Body Quantum Problem
Acta Applicandae Mathematicae 48: 113±184, 1997. 113 c 1997 Kluwer Academic Publishers. Printed in the Netherlands. Nontrivial Attractors in a Model Related to the Three-Body Quantum Problem SERGIO ALBEVERIO1,2 and KONSTANTIN A. MAKAROV1,3 1FakultatÈ furÈ Mathematik, Ruhr UniversitatÈ Bochum, D-44780 Bochum, Germany 2BiBoS; SFB 237 Bochum-Essen-Dusseldorf;È CERFIM, Locarno, Italy 3Department of Computational and Mathematical Physics, St. Petersburg University, 198094 St. Petersburg, Russia (Received: 29 January 1996) Abstract. A model of a quantum mechanical system related to the three-body problem is studied. The model is de®ned in terms of a symmetric pseudo-differential operator (PDO) with unbounded symbol. The entire family of self-adjoint extensions of this operator is studied using harmonic analysis. A regularization procedure for this PDO is introduced and the spectral properties of the operators obtained in this way are investigated. The limit behavior of the regularized operators when the regularization parameter is removed is analyzed and a nontrivial attractor is exhibited. Mathematics Subject Classi®cations (1991). 47A20, 47B35, 81Q10. Key words: extension theory of symmetric operators, convolutions, pseudo-differential operators, harmonic analysis, E®mov effect, three-body quantum problem, regularization, attractors, Hamil- tonians which are not lower semibounded, spectral analysis, Lagrangian planes. 0. Introduction In 1933, Wigner [1] remarked that nuclear forces must be of very short range and very strong. Two years later, Bethe and Peierls [2] in order to model such forces introduced point potentials that vanish except at the origin and so correspond to zero range forces. The introduction of zero-range potentials gave a powerful impulse to study quantum mechanical systems with singular interaction, many of which being also solvable [3].