584 research outputs found
Optimal control of linear stochastic evolution equations in Hilbert spaces and uniform observability
summary:In this paper we study the existence of the optimal (minimizing) control for a tracking problem, as well as a quadratic cost problem subject to linear stochastic evolution equations with unbounded coefficients in the drift. The backward differential Riccati equation (BDRE) associated with these problems (see \cite {chen}, for finite dimensional stochastic equations or \cite {UC}, for infinite dimensional equations with bounded coefficients) is in general different from the conventional BDRE (see \cite {1990}, \cite {ukl}). Under stabilizability and uniform observability conditions and assuming that the control weight-costs are uniformly positive, we establish that BDRE has a unique, uniformly positive, bounded on and stabilizing solution. Using this result we find the optimal control and the optimal cost. It is known \cite {ukl} that uniform observability does not imply detectability and consequently our results are different from those obtained under detectability conditions (see \cite {1990})
Controllability Metrics on Networks with Linear Decision Process-type Interactions and Multiplicative Noise
This paper aims at the study of controllability properties and induced
controllability metrics on complex networks governed by a class of (discrete
time) linear decision processes with mul-tiplicative noise. The dynamics are
given by a couple consisting of a Markov trend and a linear decision process
for which both the "deterministic" and the noise components rely on
trend-dependent matrices. We discuss approximate, approximate null and exact
null-controllability. Several examples are given to illustrate the links
between these concepts and to compare our results with their continuous-time
counterpart (given in [16]). We introduce a class of backward stochastic
Riccati difference schemes (BSRDS) and study their solvability for particular
frameworks. These BSRDS allow one to introduce Gramian-like controllability
metrics. As application of these metrics, we propose a minimal
intervention-targeted reduction in the study of gene networks
On the Mathematical Theory of Ensemble (Linear-Gaussian) Kalman-Bucy Filtering
The purpose of this review is to present a comprehensive overview of the
theory of ensemble Kalman-Bucy filtering for linear-Gaussian signal models. We
present a system of equations that describe the flow of individual particles
and the flow of the sample covariance and the sample mean in continuous-time
ensemble filtering. We consider these equations and their characteristics in a
number of popular ensemble Kalman filtering variants. Given these equations, we
study their asymptotic convergence to the optimal Bayesian filter. We also
study in detail some non-asymptotic time-uniform fluctuation, stability, and
contraction results on the sample covariance and sample mean (or sample error
track). We focus on testable signal/observation model conditions, and we
accommodate fully unstable (latent) signal models. We discuss the relevance and
importance of these results in characterising the filter's behaviour, e.g. it's
signal tracking performance, and we contrast these results with those in
classical studies of stability in Kalman-Bucy filtering. We provide intuition
for how these results extend to nonlinear signal models and comment on their
consequence on some typical filter behaviours seen in practice, e.g.
catastrophic divergence
Approximately Reachable Directions for Piecewise Linear Switched Systems
This paper deals with some reachability issues for piecewise linear switched
systems with time-dependent coefficients and multiplicative noise. Namely, it
aims at characterizing data that are almost reachable at some fixed time T > 0
(belong to the closure of the reachable set in a suitable L 2-sense). From a
mathematical point of view, this provides the missing link between approximate
controllability towards 0 and approximate controllability towards given
targets. The methods rely on linear-quadratic control and Riccati equations.
The main novelty is that we consider an LQ problem with controlled backward
stochastic dynamics and, since the coefficients are not deterministic (unlike
some of the cited references), neither is the backward stochastic Riccati
equation. Existence and uniqueness of the solution of such equations rely on
structure arguments (inspired by [7]). Besides solvability, Riccati
representation of the resulting control problem is provided as is the synthesis
of optimal (non-Markovian) control. Several examples are discussed
Stabilizing Solution for a Discrete-Time Modified Algebraic Riccati Equation in Infinite Dimensions
We provide necessary and sufficient conditions for the existence of stabilizing solutions for a class of modified algebraic discretetime Riccati equations (MAREs) defined on ordered Banach spaces of sequences of linear and bounded operators. These MAREs arise in the study of linear quadratic (LQ) optimal control problems for infinite-dimensional discrete-time linear systems (DTLSs) affected simultaneously by multiplicative white noise (MN) and Markovian jumps (MJs). Unlike most of the previous works, where the detectability and observability notions are key tools for studying the global solvability of MAREs, in this paper the conditions of existence of mean-square stabilizing solutions are given directly in terms of system parameters. The methods we have used are based on the spectral theory of positive operators and the properties of trace class and compact operators. Our results generalise similar ones obtained for finite-dimensional MAREs associated with stochastic DTLSs without MJs. Also they complete and extend (in the autonomous case) former investigations concerning the existence of certain global solutions (as minimal, maximal, and stabilizing solutions) for generalized discrete-time Riccati type equations defined on infinite-dimensional ordered Banach spaces
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