Existence Theorems and Galerkin Approximation for Non-Linear Evolution Control Problems

This article presents an optimization problem involving a system governed by a non-linear parabolic equation (dy/dt) + Ay = u where A is a radially continuous, monotone and coercive Volterra operator with the cost functional weakly lower semi-continuous and radially unbounded (coercive). In a first preparatory part of the article we prove two existence theorems. In the second part we present the Galerkin approximation and we prove existence of the weak and strong condensation points of a set of solution of the approximate optimization problems. Each of this points is a solution of the initial optimization problem. Finally we shall give examples using the obtained results.     

Recovery type superconvergence and a posteriori error estimates for control problems governed by Stokes equations

In this paper, we derive recovery type superconvergence analysis and a posteriori error estimates for the finite element approximation of the distributed optimal control governed by Stokes equations. We obtain superconvergence results and asymptotically exact a posteriori error estimates by applying two recovery methods, which are the patch recovery technique and the least-squares surface fitting method. Our results are based on some regularity assumption for the Stokes control problems and are applicable to the first order conforming finite element method with regular but nonuniform partitions.     

The work of calogero vinti in approximation theory and its impact in calculus of variations

Here we give a survey of Calogero Vinti's results about approximation theory and its applications in Calculus of Variation, in particular approximation in variation, perimeter, lenght and area.     

Local invariants of smooth control systems

Methods are presented for locally studying smooth nonlinear control systems on the manifoldM. The technique of chronological calculus is intensively exploited. The concept of chronological connection is introduced and is used when obtaining the invariant expressions in the form of Lie bracket polynomials for high-order variations of a nonlinear control system. The theorem on adduction of a family of smooth vector fields to the canonical form proved in Section 4 is then applied to the construction of a nilpotent polynomial approximation for a control system. Finally, the relation between the attainable sets of an original system and an approximating one is established; it implies some conclusions on the local controllability of these systems.     

Internal approximation of quasi-variational inequalities

Summary In this paper the internal approximation of a quasi-variational inequality is considered. An algorithm of Bensoussan-Lions type is proposed for which the convergence is proved. These results are applied to Signorini problem with friction for which two error estimates and numerical examples are also given.     

On a long-standing conjecture by Pólya–Szegö and related topics

The electrostatic capacity of a convex body is usually not simple to compute. We discuss two possible approximations of it. The first one is related to a long-standing conjecture by Pólya–Szegö. It states that, among all convex bodies, the “worst shape” for the approximation exists and is the planar disk. We prove the first part of this conjecture, and we establish some related results which give further evidence for the validity of the second part. We also suggest some complementary conjectures and open problems. The second approximation we study is based on the use of web functions.Received: September 29, 2003     

Riemannian metric of the averaged energy minimization problem in orbital transfer with low thrust

This article deals with the optimal transfer of a satellite between Keplerian orbits using low propulsion and is based on preliminary results of Epenoy et al. (1997) where the optimal trajectories of the energy minimization problem are approximated using averaging techniques. The averaged Hamiltonian system is explicitly computed. It is related to a Riemannian problem whose distance is an approximation of the value function. The extremal curves are analyzed, proving that the system remains integrable in the coplanar case. It is also checked that the metric associated with coplanar transfers towards a circular orbit is flat. Smoothness of small Riemannian spheres ensures global optimality of the computed extremals.     

Approximation in the mean by convex functions

We give elementary proofs for the existence and uniqueness of the best L₁-approximation to a continuous function from the class of convex functions on a closed interval, and describe thebest approximation in terms of certain piecewise linear functions.     

On an isoperimetric inequality for capacity conjectured by Pólya and Szegö

We study a conjecture by Pólya and Szegö on the approximation of the electrostatic capacity of convex bodies in terms of their surface measure. We prove that a “local version” of this conjecture holds true and we give some results which bring further evidence to its global validity.     

Nonlinear BVPS with functional parameters

We study the existence, nonexistence and properties of solutions for a certain class of second-order ODEs and their dependence on functional parameters, also in the case when nonlinearities are, in some sense, singular. This approach is based on variational methods and cover both sublinear and superlinear cases. We develop a duality theory and variational principles for this problem. As a consequence of the duality theory we give a numerical version of the variational principle which enables approximation of the solution for our problem. We apply these results to obtain the existence of bounded, radial and positive classical solutions for the BVP of elliptic type. Observe that our method allows us to investigate a certain class of elliptic systems in both bounded annular domain and exterior domain.