2,247 research outputs found
A Numerical Scheme for Invariant Distributions of Constrained Diffusions
Reflected diffusions in polyhedral domains are commonly used as approximate
models for stochastic processing networks in heavy traffic. Stationary
distributions of such models give useful information on the steady state
performance of the corresponding stochastic networks and thus it is important
to develop reliable and efficient algorithms for numerical computation of such
distributions. In this work we propose and analyze a Monte-Carlo scheme based
on an Euler type discretization of the reflected stochastic differential
equation using a single sequence of time discretization steps which decrease to
zero as time approaches infinity. Appropriately weighted empirical measures
constructed from the simulated discretized reflected diffusion are proposed as
approximations for the invariant probability measure of the true diffusion
model. Almost sure consistency results are established that in particular show
that weighted averages of polynomially growing continuous functionals evaluated
on the discretized simulated system converge a.s. to the corresponding
integrals with respect to the invariant measure. Proofs rely on constructing
suitable Lyapunov functions for tightness and uniform integrability and
characterizing almost sure limit points through an extension of Echeverria's
criteria for reflected diffusions. Regularity properties of the underlying
Skorohod problems play a key role in the proofs. Rates of convergence for
suitable families of test functions are also obtained. A key advantage of
Monte-Carlo methods is the ease of implementation, particularly for high
dimensional problems. A numerical example of a eight dimensional Skorohod
problem is presented to illustrate the applicability of the approach
Competing particle systems evolving by interacting L\'{e}vy processes
We consider finite and infinite systems of particles on the real line and
half-line evolving in continuous time. Hereby, the particles are driven by
i.i.d. L\'{e}vy processes endowed with rank-dependent drift and diffusion
coefficients. In the finite systems we show that the processes of gaps in the
respective particle configurations possess unique invariant distributions and
prove the convergence of the gap processes to the latter in the total variation
distance, assuming a bound on the jumps of the L\'{e}vy processes. In the
infinite case we show that the gap process of the particle system on the
half-line is tight for appropriate initial conditions and same drift and
diffusion coefficients for all particles. Applications of such processes
include the modeling of capital distributions among the ranked participants in
a financial market, the stability of certain stochastic queueing and storage
networks and the study of the Sherrington--Kirkpatrick model of spin glasses.Comment: Published in at http://dx.doi.org/10.1214/10-AAP743 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Heavy-tailed Distributions In Stochastic Dynamical Models
Heavy-tailed distributions are found throughout many naturally occurring
phenomena. We have reviewed the models of stochastic dynamics that lead to
heavy-tailed distributions (and power law distributions, in particular)
including the multiplicative noise models, the models subjected to the
Degree-Mass-Action principle (the generalized preferential attachment
principle), the intermittent behavior occurring in complex physical systems
near a bifurcation point, queuing systems, and the models of Self-organized
criticality. Heavy-tailed distributions appear in them as the emergent
phenomena sensitive for coupling rules essential for the entire dynamics
Multidimensional sticky Brownian motions as limits of exclusion processes
We study exclusion processes on the integer lattice in which particles change
their velocities due to stickiness. Specifically, whenever two or more
particles occupy adjacent sites, they stick together for an extended period of
time, and the entire particle system is slowed down until the ``collision'' is
resolved. We show that under diffusive scaling of space and time such processes
converge to what one might refer to as a sticky reflected Brownian motion in
the wedge. The latter behaves as a Brownian motion with constant drift vector
and diffusion matrix in the interior of the wedge, and reflects at the boundary
of the wedge after spending an instant of time there. In particular, this leads
to a natural multidimensional generalization of sticky Brownian motion on the
half-line, which is of interest in both queuing theory and stochastic portfolio
theory. For instance, this can model a market, which experiences a slowdown due
to a major event (such as a court trial between some of the largest firms in
the market) deciding about the new market leader.Comment: Published at http://dx.doi.org/10.1214/14-AAP1019 in the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
A Stochastic Resource-Sharing Network for Electric Vehicle Charging
We consider a distribution grid used to charge electric vehicles such that
voltage drops stay bounded. We model this as a class of resource-sharing
networks, known as bandwidth-sharing networks in the communication network
literature. We focus on resource-sharing networks that are driven by a class of
greedy control rules that can be implemented in a decentralized fashion. For a
large number of such control rules, we can characterize the performance of the
system by a fluid approximation. This leads to a set of dynamic equations that
take into account the stochastic behavior of EVs. We show that the invariant
point of these equations is unique and can be computed by solving a specific
ACOPF problem, which admits an exact convex relaxation. We illustrate our
findings with a case study using the SCE 47-bus network and several special
cases that allow for explicit computations.Comment: 13 pages, 8 figure
Qualitative properties of -fair policies in bandwidth-sharing networks
We consider a flow-level model of a network operating under an -fair
bandwidth sharing policy (with ) proposed by Roberts and
Massouli\'{e} [Telecomunication Systems 15 (2000) 185-201]. This is a
probabilistic model that captures the long-term aspects of bandwidth sharing
between users or flows in a communication network. We study the transient
properties as well as the steady-state distribution of the model. In
particular, for , we obtain bounds on the maximum number of flows
in the network over a given time horizon, by means of a maximal inequality
derived from the standard Lyapunov drift condition. As a corollary, we
establish the full state space collapse property for all . For the
steady-state distribution, we obtain explicit exponential tail bounds on the
number of flows, for any , by relying on a norm-like Lyapunov
function. As a corollary, we establish the validity of the diffusion
approximation developed by Kang et al. [Ann. Appl. Probab. 19 (2009)
1719-1780], in steady state, for the case where and under a local
traffic condition.Comment: Published in at http://dx.doi.org/10.1214/12-AAP915 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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