arXiv subjects

Chetan D. Pahlajani

Publications and source records attributed to Chetan D. Pahlajani.

8 recordsLinked to original sources

arXiv2026

Random perturbations of systems with periodic impulse effects

The principal aim of the present work is to explore limit theorems for small random perturbations of periodically kicked dynamical systems, in the limit of vanishing noise intensity. Recasting our system, which is described heuristically by an ordinary differential equation forced by a periodic train of delta spikes, in terms of an impulsive system with resetting, we consider small state-dependent Brownian perturbations of this system and explore the zero noise limit on finite, but arbitrary, time horizons. For the resulting nonlinear stochastic system with impulse effects, we prove convergence to the underlying deterministic nonlinear impulsive system as the noise goes to zero. More importantly, we prove convergence of the rescaled fluctuation process about the deterministic limit, in a strong pathwise sense on finite time intervals, to a limiting fluctuation process governed by a linear time-dependent stochastic differential equation in between impulses and a linear time-dependent resetting map at impulses. In each of these cases, we are able to obtain rigorous estimates on the remainders. Our results thus provide quantitative tools to accurately and efficiently approximate small random fluctuations of the original nonlinear stochastic impulsive system about the deterministic limit in terms of linear, albeit time-inhomogeneous, surrogates. The results are illustrated numerically for two different examples: a periodically kicked nonlinear pendulum with state-dependent kick sizes and a FitzHugh-Nagumo system subject to periodic kicks.

math.PR↗

arXiv2026

Fluctuation analysis for a randomly perturbed dynamical system with state-dependent impulse effects

The principal aim of the present work is to explore limit theorems for small random perturbations of a planar impulsive dynamical system, where impulses occur at hitting times of a suitable switching surface, and are thus state-dependent. Working with a simplified example in polar coordinates, we obtain-for any fixed time horizon-a small noise expansion for the radial component, together with rigorous error estimates in the Skorohod space of right-continuous functions with left limits.

math.PR↗

arXiv2025

Periodic Homogenization for Switching Diffusions

In the present work, we explore homogenization techniques for a class of switching diffusion processes whose drift and diffusion coefficients, and jump intensities are smooth, spatially periodic functions; we assume full coupling between the continuous and discrete components of the state. Under the assumptions of uniform ellipticity of the diffusion matrices and irreducibility of the matrix of switching intensities, we explore the large-scale long-time behavior of the process under a diffusive scaling. Our main result characterizes the limiting fluctuations of the rescaled continuous component about a constant velocity drift by an effective Brownian motion with explicitly computable covariance matrix. In the process of extending classical periodic homogenization techniques for diffusions to the case of switching diffusions, our main quantitative finding is the computation of an extra contribution to the limiting diffusivity stemming from the switching.

math.PR↗

arXiv2022

Fluctuation analysis for a class of nonlinear systems with fast periodic sampling and small state-dependent white noise

We consider a nonlinear differential equation under the combined influence of small state-dependent Brownian perturbations of size $\varepsilon$, and fast periodic sampling with period $δ$; $0<\varepsilon, δ\ll 1$. Thus, state samples (measurements) are taken every $δ$ time units, and the instantaneous rate of change of the state depends on its current value as well as its most recent sample. We show that the resulting stochastic process indexed by $\varepsilon,δ$, can be approximated, as $\varepsilon,δ\searrow 0$, by an ordinary differential equation (ODE) with vector field obtained by replacing the most recent sample by the current value of the state. We next analyze the fluctuations of the stochastic process about the limiting ODE. Our main result asserts that, for the case when $δ\searrow 0$ at the same rate as, or faster than, $\varepsilon \searrow 0$, the rescaled fluctuations can be approximated in a suitable strong (pathwise) sense by a limiting stochastic differential equation (SDE). This SDE varies depending on the exact rates at which $\varepsilon,δ\searrow 0$. The key contribution here involves computing the effective drift term capturing the interplay between noise and sampling in the limiting SDE. The results essentially provide a first-order perturbation expansion, together with error estimates, for the stochastic process of interest. Connections with the performance analysis of feedback control systems with sampling are discussed and illustrated numerically through a simple example.

math.PR↗

arXiv2021

Approximation of linear controlled dynamical systems with small random noise and fast periodic sampling

In this paper, we study the dynamics of a linear control system with given state feedback control law in the presence of fast periodic sampling at temporal frequency $1/δ$ ($0 < δ\ll 1$), together with small white noise perturbations of size $\varepsilon$ ($0<\varepsilon \ll 1$) in the state dynamics. For the ensuing continuous-time stochastic process indexed by two small parameters $\varepsilon,δ$, we obtain effective ordinary and stochastic differential equations describing the mean behavior and the typical fluctuations about the mean in the limit as $\varepsilon,δ\searrow 0$. The effective fluctuation process is found to vary, depending on whether $δ\searrow 0$ faster than/at the same rate as/slower than $\varepsilon \searrow 0$. The most interesting case is found to be the one where $δ,\varepsilon$ are comparable in size; here, the limiting stochastic differential equation for the fluctuations has both a diffusive term due to the small noise and an effective drift term which captures the cumulative effect of the fast sampling. In this regime, our results yield a time-inhomogeneous Markov process which provides a strong (pathwise) approximation of the original non-Markovian process, together with estimates on the ensuing error. A simple example involving an infinite time horizon linear quadratic regulation problem illustrates the results.

math.PR↗

arXiv2016

Randomly perturbed switching dynamics of a DC/DC converter

In this paper, we study the effect of small Brownian noise on a switching dynamical system which models a first-order DC/DC buck converter. The state vector of this system comprises a continuous component whose dynamics switch, based on the ON/OFF configuration of the circuit, between two ordinary differential equations (ODE), and a discrete component which keeps track of the ON/OFF configurations. Assuming that the parameters and initial conditions of the unperturbed system have been tuned to yield a stable periodic orbit, we study the stochastic dynamics of this system when the forcing input in the ON state is subject to small white noise fluctuations of size $\varepsilon$, $0<\varepsilon \ll 1$. For the ensuing stochastic system whose dynamics switch at random times between a small noise stochastic differential equation (SDE) and an ODE, we prove a functional law of large numbers which states that in the limit of vanishing noise, the stochastic system converges to the underlying deterministic one on time horizons of order $\mathscr{O}(1/\varepsilon^ν)$, $0 \le ν< 2/3$.

math.PR↗

arXiv2012

Stochastic receding horizon control of nonlinear stochastic systems with probabilistic state constraints

The paper describes a receding horizon control design framework for continuous-time stochastic nonlinear systems subject to probabilistic state constraints. The intention is to derive solutions that are implementable in real-time on currently available mobile processors. The approach consists of decomposing the problem into designing receding horizon reference paths based on the drift component of the system dynamics, and then implementing a stochastic optimal controller to allow the system to stay close and follow the reference path. In some cases, the stochastic optimal controller can be obtained in closed form; in more general cases, pre-computed numerical solutions can be implemented in real-time without the need for on-line computation. The convergence of the closed loop system is established assuming no constraints on control inputs, and simulation results are provided to corroborate the theoretical predictions.

eess.SY↗

arXiv2012

Networked Decision Making for Poisson Processes: Application to nuclear detection

This paper addresses a detection problem where several spatially distributed sensors independently observe a time-inhomogeneous stochastic process. The task is to decide between two hypotheses regarding the statistics of the observed process at the end of a fixed time interval. In the proposed method, each of the sensors transmits once to a fusion center a locally processed summary of its information in the form of a likelihood ratio. The fusion center then combines these messages to arrive at an optimal decision in the Neyman-Pearson framework. The approach is motivated by applications arising in the detection of mobile radioactive sources, and offers a pathway toward the development of novel fixed- interval detection algorithms that combine decentralized processing with optimal centralized decision making.

math.PR↗