on the characterization of sampled data controllers in the lifted domain abstract in this paper we address sampled data control problems on which the sampling and hold devices are not fixed before hand but are chosen as part of the design process the idea is to apply the lifting transformation to the plant and then characterize the set of generalized sampled data controllers i e those that can be implemented as the cascade of a generalized sampler a discrete time controller and a generalized hold we argue that our approach offers significant advantages over previous works and will illustrate this by considering three applications the input output stabilization by generalized sampled data controllers the solution of the h optimal control problem and the combination of analog and digital controllers

h sub infinity optimal control with state feedback a h sub infinity optimal control problem in which the measured outputs are the states of the plant is considered the main result shows that the infimum of the norm of the closed loop transfer function using linear static state feedback equals the infimum of the norm of the closed loop transfer function over all stabilizing dynamic even nonlinear time varying state feedback controllers

lqg control with an h sup infinity performance bound a riccati equation approach an lqg linear quadratic gaussian control design problem involving a constraint on h sup infinity disturbance attenuation is considered the h sup infinity performance constraint is embedded within the optimization process by replacing the covariance lyapunov equation by a riccati equation whose solution leads to an upper bound on l sub 2 performance in contrast to the pair of separated riccati equations of standard lqg theory the h sup infinity constrained gains are given by a coupled system of three modified riccati equations the coupling illustrates the breakdown of the separation principle for the h sup infinity constrained problem both full and reduced order design problems are considered with an h sup infinity attenuation constraint involving both state and control variables an algorithm is developed for the full order design problem and illustrative numerical results are given

an algebraic riccati equation approach to h optimization abstract this paper considers the general so called four block h optimal control problem with the assumption that system states are available for feedback it is shown that infimization of the h norm of the closed loop transfer function over all linear constant i e nondynamic stabilizing state feedback laws can be completely characterized via an algebraic riccati equation it is further shown that the optimal norm is not improved by allowing feedback to be dynamic thus the general state feedback h optimal control problem can be solved by iteratively solving one are and the controller can be chosen to be static gain

decay rates for the three dimensional linear system of thermoelasticity we consider the two and three dimensional system of linear thermoelasticity in a bounded smooth domain with dirichlet boundary conditions we analyze whether the energy of solutions decays exponentially uniformly to zero as t to infty first of all by a decoupling method we reduce the problem to an observability inequality for the lame system in linear elasticity and more precisely to whether the total energy of the solutions can be estimated in terms of the energy concentrated on its longitudinal component we show that when the domain is convex the decay rate is never uniform in fact the lack of uniform decay holds in a more general class of domains in which there exist rays of geometric optics of arbitrarily large length that are always reflected perpendicularly or almost tangentially on the boundary we also show that in three space dimensions the lack of uniform decay may also be due to a critical polarization of the energy on the transversal component of the displacement in two space dimensions we prove a sufficient and almost necessary condition for the uniform decay to hold in terms of the propagation of the transversal characteristic rays under the further assumption that the boundary of the domain does not have contacts of infinite order with its tangents we also give an example due to d hulin in which these geometric properties hold in three space dimensions we indicate without proof how a careful analysis of the polarization of singularities may lead to sharp sufficient conditions for the uniform decay to hold in two space dimensions we prove that smooth solutions decay polynomially in the energy space to a finite dimensional subspace of solutions except when the domain is a ball or an annulus finally we discuss some closely related controllability and spectral issues

h output feedback control of fuzzy system models under sampled measurements this paper studies the problem of control for a class of fuzzy system models by using a linear output controller the system under consideration is described by a continuous time fuzzy system model under sampled output measurements the premise variables of the fuzzy system model are assumed unmeasurable we develop a technique for designing an output feedback control law which globally stabilises this class of fuzzy system models a design algorithm for constructing the linear output controller is given a numerical simulation example is given to show the potential of the proposed techniques

almost periodic solutions to some semilinear non autonomous thermoelastic plate equations abstract the paper is concerned with the existence of almost periodic solutions to the so called semilinear thermoelastic plate systems for that the strategy consists of seeing these systems as a particular case of the semilinear parabolic evolution equations x t a t x t f t x t t r where a t for t r is a family of sectorial linear operators on a banach space x satisfying the so called acquistapace terreni conditions and f is a function defined on a real interpolation space x for 0 1 under some reasonable assumptions it will be shown that has a unique almost periodic solution we then make use of the previous result to obtain the existence and uniqueness of an almost periodic solution to the thermoelastic plate systems

existence stability and smoothness of a bounded solution for nonlinear time varying thermoelastic plate equations in this paper we study the existence stability and the smoothness of a bounded solution of the following nonlinear time varying thermoelastic plate equation with homogeneous dirichlet boundary conditions utt 2u f1 t u t 0 x t ut f2 t u t 0 x u u 0 t 0 x where 0 0 is a sufficiently regular bounded domain in rn n 1 and fe1 fe2 r l2 2 l2 define by fe t u x f t u x x x are continuous and locally lipschitz functions first we prove that the linear system f1 f2 0 generates an analytic strongly continuous semigroup which decays exponentially to zero second under some additional condition we prove that the nonlinear system has a bounded solution which is exponentially stable and for a large class of functions f1 f2 this bounded solution is almost periodic finally we use the analyticity of the semigroup generated by the linear system to prove the smoothness of the bounded solution

performance analysis of sampled data control systems abstract this brief paper considers multivariable sampled data systems with bandlimited exogenous inputs a procedure is given for the computation of the l 2 induced input to output norm of such a system in addition sufficient conditions are given for input output stability the digital implementation of an analog controller will generally degrade the performance of the closed loop system in light of this two examples are given to illustrate how this degradation is quantified as a function of the sampling period in general this allows the determination of the minimum sampling rate required to recover the performance designed for using the original continuous time setup

on the l 2 induced norm of a sampled data system formulas are given for the norms of sg and gh g is a linear continuous time system s an ideal sampler and h a zero order hold the signal spaces are l2 continuous time and l2 z discrete time these formulas are then applied to problems of uniformly optimal control of sampled data systems

existence of weighted pseudo anti periodic solutions to some non autonomous differential equations abstract in this paper we first introduce two new concepts called respectively weighted pseudo periodicity and weighted pseudo anti periodicity which generalize respectively the well known notions of periodicity and that of anti periodicity basic properties of these new functions are discussed furthermore the existence of weighted pseudo anti periodic solutions to some damped non autonomous second order differential equations will be investigated to illustrate our abstract results the existence of weighted pseudo anti periodic solutions to a plate like equation is discussed

on the existence of speed independent circuits abstract a circuit is called speed independent if its nontransient behavior does not depend on the size of the delays in the different components of the circuit we show that the class of speed independent circuits is relatively small in fact very many useful circuits cannot be realized in a speed independent design for example we show that there does not exist any speed independent mod k counter for any k 1 the results are derived using a very general model of a network which is applicable to both gate circuits and more modern mos switch level circuits furthermore the results are also robust with respect to different delay assumptions and definitions of speed independence

l_ 1 discretization for sampled data controller synthesis via piecewise linear approximation this paper develops a new discretization method with piecewise linear approximation for the l 1 optimal controller synthesis problem of sampled data systems which is the problem of minimizing the l infty induced norm of sampled data systems we apply fast lifting on the top of the lifting technique by which the sampling interval 0 h is divided into m subintervals with an equal width the signals on each subinterval are then approximated by linear functions by introducing two types of linearizing operators for input and output which leads to piecewise linear approximation of sampled data systems by using the arguments of preadjoint operators we provide an important inequality that forms a theoretical basis for tackling the l 1 optimal controller synthesis problem of sampled data systems more efficiently than the conventional method more precisely a mathematical basis for the piecewise linear approximation method associated with the convergence rate is shown through this inequality and this suggests that the piecewise linear approximation method may drastically outperform the conventional method in the l 1 optimal controller synthesis problem of sampled data systems we then provide a discretization procedure of sampled data systems by which the l 1 optimal controller synthesis problem is converted to the discrete time l 1 optimal controller synthesis problem finally effectiveness of the proposed method is demonstrated through a numerical example

initial boundary value problems and optimal control for nonautonomous parabolic systems a large class of linear nonautonomous parabolic systems in bounded domains is considered with control acting on the boundary through dirichlet or neumann conditions from the point of view of semigroup theory the results from rend sem mat univ padova 78 1987 pp 47 107 on fundamental solutions for abstract parabolic equations lecture notes in math vol 1223 springer verlag berlin heidelberg 1986 pp 1 11 on abstract homogeneous parabolic cauchy problems allow operators with varying domains and holder continuous coefficients to be handled a representation formula for solutions corresponding to square integrable control functions is derived and used to solve a linear quadratic regulator problem over finite time horizon by a direct study of the associated integral riccati equation

stability and almost periodicity of trajectories of periodic processes abstract we prove that if the monodromy operator v of a linear periodic process u t in a banach space e is power bounded has countable peripheral spectrum and if its peripheral point spectrum satisfies a certain natural and simple duality condition which always holds in reflexive spaces then every positive trajectory u u 0 x 0 x e is asymptotically almost periodic if in particular the peripheral point spectrum of v is empty then every positive trajectory is asymptotically stable we also obtain results on almost periodicity of complete bounded trajectories and consider conditions under which nontrivial complete trajectories exist

intermittent redesign of analog controllers via the youla parameter the paper studies digital redesign of linear time invariant analog controllers under intermittent sampling the sampling pattern is only assumed to be uniformly bounded but otherwise irregular and unknown a priori the contribution of the paper is twofold first it proposes a constructive algorithm to redesign any analog stabilizing controller so that the closed loop stability is preserved second it is shown that when applied to sub optimal boldsymbol h 2 and boldsymbol h infty controllers the algorithm produces sub optimal sampled data solutions under any a priori unknown sampling pattern the proposed solutions are analytic computationally simple implementable and transparent transparency pays off in showing the optimality under a fixed sampling density of uniform sampling for both performance measures studied

h and lgq control of asynchronous sampled data systems a class of dual rate sampled data systems is considered where the sampling rate is asynchronously related to the rate at which the hold element is operating such asynchronous sampled data systems are aperiodic and hence the lifting technique which is used to represent synchronous sampled data systems as single rate discrete systems cannot be applied to the asynchronous case in this study optimal h and lqg controllers for asynchronous sampled data systems are derived using a two riccati equation approach which does not rely on the lifting method a distribution theorem is used to evaluate the optimal stationary performance levels in the two cases

the undecidability of the second order unification problem abstract it is shown that there is no effective procedure for determining whether or not two terms of the language of second order logic have a common instance

a game theoretic approach to h control for time varying systems a representation formula for all controllers that satisfy an mathcal l infty type constraint is derived for time varying systems it is now known that a formula based on two indefinite algebraic riccati equations may be found for time invariant systems over an infinite time support see j c doyle et al ieee trans automat control ac 34 1989 pp 831 847 k glover and j c doyle systems control lett 11 1988 pp 167 172 k glover et al siam j control optim 29 1991 pp 283 324 m green et al siam j control optim 28 1990 pp 1350 1371 d j n limebeer et al in proc ieee conf on decision and control austin tx 1988 g tadmor math control systems signal processing 3 1990 pp 301 324 in the time varying case two indefinite riccati differential equations are required a solution to the design problem exists if these equations have a solution on the optimization interval the derivation of the representation formula illustrated in this paper mak

further results on the l 1 analysis of sampled data systems via kernel approximation approach abstractthis paper gives two methods for the l1 analysis of sampled data systems by which we mean computing the l induced norm of sampled data systems this is achieved by developing what we call the kernel approximation approach in the setting of sampled data systems we first consider the lifting treatment of sampled data systems and give an operator theoretic representation of their input output relation we further apply the fast lifting technique by which the sampling interval 0 h is divided into m subintervals with an equal width and provide methods for computing the l induced norm in contrast to a similar approach developed earlier called the input approximation approach we use an idea of kernel approximation in which the kernel function of an input operator and the hold function of an output operator are approximated by piecewise constant or piecewise linear functions furthermore it is shown that the approximation errors in the piecewise constant approximation or piecewise linear appro

a characteristic equation for non autonomous partial functional differential equations abstract we characterize the exponential dichotomy of non autonomous partial functional differential equations by means of a spectral condition extending known characteristic equations for the autonomous or time periodic case from this we deduce robustness results we further study the almost periodicity of solutions to the inhomogeneous equation our approach is based on the spectral theory of evolution semigroups

boundary controllability of thermoelastic plates via the free boundary conditions controllability properties of a partial differential equation pde model describing a thermoelastic plate are studied the pde is composed of a kirchoff plate equation coupled to a heat equation on a bounded domain with the coupling taking place on the interior and boundary of the domain the coupling in this pde is parameterized by alpha 0 boundary control is exerted through the two free boundary conditions of the plate equation and through the robin boundary condition of the temperature these controls have the physical interpretation of inserted forces and moments and prescribed temperature respectively all of which act on the edges of the plate the main result here is that under such boundary control and with initial data in the basic space of well posedness one can simultaneously control the displacement of the plate exactly and the temperature approximately moreover the thermal control may be taken to be arbitrarily smooth in time and space and the thermal control region may be any nonempty subset of the boundary this controllability holds for arbitrary values of the coupling parameter alpha with the optimal controllability time in line with that seen for uncoupled kirchoff plates

referential logic of proofs we introduce an extension of the propositional logic of single conclusion proofs by the second order variables denoting the reference constructors of the type the formula which is proved by x the resulting logic of proofs with references flpref is shown to be decidable and to enjoy soundness and completeness with respect to the intended provability semantics we show that flpref provides a complete test of admissibility of inference rules in a sound extension of arithmetic this paper may be regarded as a contribution to the theory of automated reasoning systems

sensitivity minimization in an h norm parametrization of all suboptimal solutions a number of problems in the control of linear feedback systems can be reduced to the following we are given three stable rational matrix functions k of sizes p 1 x q 1 p 1 x q 2 and p 2 x q 1 respectively and seek a stable rational q 2 x p 2 matrix function s so as to minimize k s we assume that p 1 q 2 p 2 q 1 and that and have maximal rank q 2 and p 2 respectively on the j axis given a tolerance level sufficiently large we obtain a linear fractional map g f 0 11 g 0 12 0 13 0 21 g 0 22 0 23 1 such that f k s with s stable and f if and only if g is a stable q 2 x p 2 matrix function with g 1 the computation of 0 0 ij 1 i 2 1 j 3 reduces to solving a pair of symmetric wiener hopf factorization problems for the special case where i q2 0 t i p2 0 and k not necessarily stable to which the general case can be reduced we provide explicit state space formulae for 0 in terms of a state space realization of k and the

simplifying the h theory via loop shifting matrix pencil and descriptor concepts the 2 riccati h controller formulae and derivations are simplified via various loop shifting transformations that are naturally expressed in terms of a degree one polynomial system matrix psm closely related to the luenberger descriptor form of a system the technique enables one without loss of generality to restrict attention to the simple case in which d 11 0 d 22 0 d t 12 0 l d 21 0 l d l 12 c1 0 and b 1 d t 21 0 matrix fraction descriptions mfds for the algebraic riccati equation solutions afford another change of variables which brings the 2 riccati h controller formulae into a cleaner more symmetric descriptor form having the important practical advantage that it eliminates the numerical difficulties that can occur in cases where one or both of the riccati solutions pi and q blow up and in cases where l qp is nearly singular numerical difficulties previously associated with verifying the existence conditions p 0 q 0 and maxlpar qp 1 are largely eliminated by e

almost periodicity of mild solutions of inhomogeneous periodic cauchy problems abstract we consider a mild solution u of a well posed inhomogeneous cauchy problem u t a t u t f t on a banach space x where a is periodic for a problem on r we show that u is asymptotically almost periodic if f is asymptotically almost periodic u is bounded uniformly continuous and totally ergodic and the spectrum of the monodromy operator v contains only countably many points of the unit circle for a problem on r we show that a bounded uniformly continuous solution u is almost periodic if f is almost periodic and various supplementary conditions are satisfied we also show that there is a unique bounded solution subject to certain spectral assumptions on v f and u

robust stabilization of uncertain linear systems quadratic stabilizability and h sup infinity control theory the problem of robustly stabilizing a linear uncertain system is considered with emphasis on the interplay between the time domain results on the quadratic stabilization of uncertain systems and the frequency domain results on h sup infinity optimization a complete solution to a certain quadratic stabilization problem in which uncertainty enters both the state and the input matrices of the system is given relations between these robust stabilization problems and h sup infinity control theory are explored it is also shown that in a number of cases if a robust stabilization problem can be solved via lyapunov methods then it can be also be solved via h sup infinity control theory based methods

state space solutions to standard h sub 2 and h sub infinity control problems simple state space formulas are derived for all controllers solving the following standard h sub infinity problem for a given number gamma 0 find all controllers such that the h sub infinity norm of the closed loop transfer function is strictly less than gamma it is known that a controller exists if and only if the unique stabilizing solutions to two algebraic riccati equations are positive definite and the spectral radius of their product is less than gamma sup 2 under these conditions a parameterization of all controllers solving the problem is given as a linear fractional transformation lft on a contractive stable free parameter the state dimension of the coefficient matrix for the lft constructed using the two riccati solutions equals that of the plant and has a separation structure reminiscent of classical lqg i e h sub 2 theory this paper is intended to be of tutorial value so a standard h sub 2 solution is developed in parallel

on the central controller characterizations via differential games and leqg control problems abstract we provide a game theoretic interpretation to the central controller which plays a central role in characterizing all controllers achieving disturbance attenuation in the sense of the h norm in the imperfect observation case we also establish a direct relation between the central controller and the stationary leqg controller for continuous time systems

h optimal sampled data control in continuous time systems we consider the design of h optimal discrete time digital controllers in continuous time systems an apparent difficulty especially in utilizing modern transform domain analysis in this context stems from the absence of an appropriate transfer function model for the hybrid time discrete and continuous closed loop system this difficulty is overcome through the introduction of an equivalent difference equation model for the continuous time system with distributed inputs and outputs equivalence being in the sense that the continuous and discrete time inputs and outputs are essentially identical using the interplay between the discrete and the continuous time models solutions of the well known purely continuous time and purely discrete time standard problems extend to solutions of the problem at hand they comprise riccati equation characterizations of feasible combinations of sampling rates and bounds on the closed loop induced input output norm and parameterization of compensators we consid

existence of weighted pseudo almost periodic solutions to some classes of nonautonomous partial evolution equations abstract in this paper under acquistapace terreni conditions we make extensive use of interpolation spaces and exponential dichotomy techniques to obtain the existence of weighted pseudo almost periodic solutions to some classes of nonautonomous partial evolution equations applications include the existence of weighted pseudo almost periodic solutions to a nonautonomous heat equation with gradient coefficients