Dissipative Control Systems and Disturbance Attenuation for Nonlinear H ∞ Problems

We characterize functions satisfying a dissipative inequality associated with a control problem. Such a characterization is provided in terms of an epicontingent solution, or a viscosity supersolution to a partial differential equation called Isaacs' equation. Links between supersolutions and epicontingent solutions to Isaacs' equation are studied. Finally, we derive (possibly discontinuous) disturbance attenuation feedback of the H ^∞ problem from contingent formulation of Isaacs' equation. Accepted 20 January 1998     

Analytic Solutions of L∞ Optimal Control Problems for the Wave Equation

There are very few results about analytic solutions of problems of optimal control with minimal L norm. In this paper, we consider such a problem for the wave equation, where the derivative of the state is controlled at both boundaries. We start in the zero position and consider a problem of exact control, that is, we want to reach a given terminal state in a given finite time. Our aim is to find a control with minimal L norm that steers the system to the target.We give the analytic solution for certain classes of target points, for example, target points that are given by constant functions. For such targets with zero velocity, the analytic solution has been given by Bennighof and Boucher in Ref. 1.     

Output Feedback H∞ Control for a Class of Nonlinear Stochastic Systems

This paper deals with the output feedback H∞ control problem for a class of nonlinear stochastic systems. Based on the latest developed theory of stochastic dissipation, a notable result about the nonlinear H∞ output feedback control of deterministic system is generalized to the stochastic case. Finally, in the cases of state feedback and output feedback, two families of controllers are provided respectively.     

Global Saturation of Regularization Methods for Inverse Ill-Posed Problems

In this article the concept of saturation of an arbitrary regularization method is formalized based upon the original idea of saturation for spectral regularization methods introduced by Neubauer (Beiträge zur angewandten Analysis und Informatik, pp. 262–270, 1994). Necessary and sufficient conditions for a regularization method to have global saturation are provided. It is shown that for a method to have global saturation the total error must be optimal in two senses, namely as optimal order of convergence over a certain set which at the same time, must be optimal (in a very precise sense) with respect to the error. Finally, two converse results are proved and the theory is applied to find sufficient conditions which ensure the existence of global saturation for spectral methods with classical qualification of finite positive order and for methods with maximal qualification. Finally, several examples of regularization methods possessing global saturation are shown.     

Superconvergence and $L^∞$-Error Estimates of the Lowest Order Mixed Methods for Distributed Optimal Control Problems Governed by Semilinear Elliptic Equations

In this paper, we investigate the superconvergence property and the $L^∞$-error estimates of mixed finite element methods for a semilinear elliptic control problem. The state and co-state are approximated by the lowest order Raviart-Thomas mixed finite element spaces and the control variable is approximated by piecewise constant functions. We derive some superconvergence results for the control variable. Moreover, we derive $L^∞$-error estimates both for the control variable and the state variables. Finally, a numerical example is given to demonstrate the theoretical results.     

Ergodic Control in L∞

The infinite horizon discounted L ^∞ problem is studied as the discount factor goes to zero. It is related to the limit of the finite horizon problem as the horizon becomes infinite. The deterministic problem with and without a running cost is considered.     

On Systems of Boundary Value Problems for Differential Inclusions

Herein we consider the existence of solutions to second-order, two-point boundary value problems （BVPs） for systems of ordinary differential inclusions. Some new Bernstein-Nagumo conditions are presented that ensure a priori bounds on the derivative of solutions to the differential inclusion. These a priori bound results are then applied, in conjunction with appropriate topological methods, to prove some new existence theorems for solutions to systems of BVPs for differential inclusions. The new conditions allow of the treatment of systems of BVPs without growth restrictions.     

Suboptimal Control of Time-Varying Neutral Control Systems

In this paper,the optimal control of time-varying neutral control systems is investigated by means of the Maxmium Principle of time-delay systems.optimal control law is given. Then sub-optimal control of time-varying neutral control systems is studied by using sensitivity approach. Algorithm for suboptimal control is given.     

Multiple Solutions for Systems of Sturm–Liouville Boundary Value Problems

In this paper, the authors discuss the existence of multiple solutions to a class of second-order Sturm–Liouville boundary value systems. Their proofs are based on variational methods and critical point theory.     

Singular Stabilization and H∞ Control of Nonlinear Systems with Ordinary Homogeneous Properties

In this paper, the nonlinear singular stabilization, H∞control problem of systems with ordinary homogeneous properties is considered. At first, we discuss the stabilization problems of nonlinear systems with homogeneous. Secondly, by vitue of Hamilton-Jacobi-Isaacs equations or inequalities, we solve regular H∞, of nonlinear systems with homogeneous properties. To overcome the H∞, problem of singular nonlinear system, we try to transform inputs of the singular nonlinear system into two parts: regular part input and singular part input. Following the previous results, we solve the singular nonlinear system H∞control, we give the Lyapunov function and the state feedback controller of the singular nonlinear systems with homogeneous properties.     

Control Synthesis for Čaplygin Polynomial Systems

This paper discusses new control synthesis for certain cascade type polynomial systems addressed in the paper as aplygin systems. A numerical control synthesis as well as characterization of reachability set are presented. The results of the paper are important for various branches of system theory, where the control synthesis is concerned.     

Construction of a Class of Finite H ∞ Controllers for Infinite-Dimensional Systems

We consider the suppression of forced oscillations in distributed systems of a hyperbolic type by finite-dimensional controllers using an H objective. The system is split into a finite-dimensional and an infinite-dimensional subsystems. The controller receives a signal from the output of both systems. The class of controllers is described in the form of a system of ordinary differential equations.     

Infinitely Many Solutions for Systems of Sturm–Liouville Boundary Value Problems

In this paper, the authors obtain the existence of infinitely many classical solutions to the boundary value system with Sturm–Liouville boundary conditions $$\left\{\begin{array}{ll}-(\phi_{p_i}(u_{i}^\prime))^\prime = \lambda F_{u_{i}}(x,u_{1},\ldots,u_{n})h_{i}(u^\prime_i)\quad {\rm in} \, (a,b), \\ \alpha_iu_{i}(a)-\beta_iu^ \prime_{i}(a)=0, \quad \gamma_iu_{i}(b)+\sigma_iu^\prime_{i}(b)=0, \end{array}\quad{i = 1, \ldots , n.} \right.$$ Critical point theory and Ricceri’s variational principle are used in the proofs.     

Asymptotic Analysis and Solution of a Finite-Horizon H ∞ Control Problem for Singularly-Perturbed Linear Systems with Small State Delay

A finite-horizon H state-feedback control problem for singularly-perturbed linear time-dependent systems with a small state delay is considered. Two approaches to the asymptotic analysis and solution of this problem are proposed. In the first approach, an asymptotic solution of the singularly-perturbed system of functional-differential equations of Riccati type, associated with the original H problem by the sufficient conditions of the existence of its solution, is constructed. Based on this asymptotic solution, conditions for the existence of a solution of the original H problem, independent of the small parameter of singular perturbations, are derived. A simplified controller with parameter-independent gain matrices, solving the original H problem for all sufficiently small values of this parameter, is obtained. In the second approach, the original H problem is decomposed into two lower-dimensional parameter-independent H subproblems, the reduced-order (slow) and the boundary-layer (fast) subproblems; controllers solving these subproblems are constructed. Based on these controllers, a composite controller is derived, which solves the original H problem for all sufficiently small values of the singular perturbation parameter. An illustrative example is presented.     

L ∞ Variational Problems with Running Costs and Constraints

Various approaches are used to derive the Aronsson–Euler equations for L ^∞ calculus of variations problems with constraints. The problems considered involve holonomic, nonholonomic, isoperimetric, and isosupremic constraints on the minimizer. In addition, we derive the Aronsson–Euler equation for the basic L ^∞ problem with a running cost and then consider properties of an absolute minimizer. Many open problems are introduced for further study.     

L∞-Estimates for the Torsion Function and L∞-Growth of Semigroups Satisfying Gaussian Bounds

Potential Analysis - We investigate selfadjoint C0-semigroups on Euclidean domains satisfying Gaussian upper bounds. Major examples are semigroups generated by second order uniformly elliptic...     

Four-Point Boundary-Value Problems for Differential–Algebraic Systems

We apply the monotone iterative method to nonlinear four-point boundary conditions for differential–algebraic systems with causal operators. Sufficient conditions under which such problems have solutions (extremal or unique) are given. An example illustrates the theoretical results.     

Categoricity results for L∞κ

Let V denote a variety of algebras in a countable language. An algebra is said to be L_∞κ-free if it is L_∞κ-equivalent to a (V-) free algebra. If every L_∞ω1-free algebra of cardinality ω₁ is free, then for all infinite cardinals κ every L_∞κ-free algebra of cardinality κ is free. Further, assuming suitable set-theoretic hypotheses, if there is a non-free L_∞ω1-free algebra of cardinality ω₁, then for a proper class of cardinals κ there are non-free L_∞κ-free algebras of cardinality κ. The varieties in which the class of free algebras are definable by a sentence in L_ω1ω are characterized as the weak Schreier varieties in which every L_∞ω-free algebra of cardinality ω₁ is free. A weak Schreier variety is one in which every L_∞ω-elementary substructure of a free algebra is free. In fact, assuming suitable set-theortic hypotheses, for weak Schreier varieties the class of free algebras is definable in L_∞∞ iff it is definable in L_ω1ω. Varieties in uncountable languages are also considered.