Successive overrelaxation method with projection for finite element solutions applied to the Dirichlet problem of the nonlinear elliptic equation Δu-bu2

this study is a continuation of a previous paper [Computing 38 (1987), pp.117–132]. In this paper, we consider the successive overrelaxation method with projection for obtaining finite element solutions applied to the Dirichlet problem of the nonlinear elliptic equation $$\begin{gathered} \Delta u = bu^2 in\Omega , \hfill \\ u = g(x)on\Gamma . \hfill \\ \end{gathered} $$ . Some numerical examples are given to illustrate the effectiveness.     

Inhomogeneous Dirichlet boundary condition in the a posteriori error control of the obstacle problem

We study a posteriori error control of finite element approximation of the elliptic obstacle problem with nonhomogeneous Dirichlet boundary condition. The results in the article are two fold. Firstly, we address the influence of the inhomogeneous Dirichlet boundary condition in residual based a posteriori error control of the elliptic obstacle problem. Secondly by rewriting the obstacle problem in an equivalent form, we derive a posteriori error bounds which are in simpler form and efficient. To accomplish this, we construct and use a post-processed solution ${\stackrel{?}{u}}_h$ of the discrete solution $u_h$ which satisfies the exact boundary conditions sharply although the discrete solution $u_h$ may not satisfy. We propose two post processing methods and analyze them, namely the harmonic extension and a linear extension. The theoretical results are illustrated by the numerical results.     

A new polynomial-time algorithm for the maximum weighted (χ(G) — 1)-coloring problem in comparability graphs

For a weighted graph G = (V, E), the maximum weightedk-coloring problem is to color a set of vertices of maximum weight usingk colors. In this paper we are interested in solving this problem in comparability graphs. For these graphs, as shown by Cameron, the problem can be translated into a dual transportation problem. Let (G) denote the chromatic number of a comparability graphG. We prove that whenk is equal to (G) — 1, the problem can be solved more efficiently by finding a maximum weighted stable set in a bipartite graph. Maximum matching algorithms can be used in the unweighted case.This work was supported by an NSERC International Fellowship to the University of Montréal, and by NSERC #OGP0105384.     

A duality-based approach to the multiobjective H 2/H ∞ optimisation problem

In this article, a duality approach to multiobjective H ₂/H _∞ problems is pursued in which real-rational, para-Hermitian multipliers and real-valued ones are associated to H _∞ and (as usual) H ₂ constraints, respectively. It is shown that the maximisation of a dual functional over all such multipliers yields the optimal value of the original multiobjective H ₂/H _∞ problem. To compute lower bounds on the latter and the corresponding approximate solutions to the original problem, the maximisation of the dual functional over linearly-parameterised, finite-dimensional classes of real-rational multipliers is shown to be equivalent to semi-definite, linear programming problems – once the optimal multipliers in such a class are obtained, the corresponding approximate solutions can be computed from an unconstrained H ₂ problem. Iterative modification of such classes is discussed to obtain increasing sequences of lower bounds on the optimal value of the original problem. This is done on the basis of (locally) increasing directions for the dual functional which go beyond the finite-dimensional class of multipliers considered in a given step. Finally, a numerical example is presented to illustrate the way the presented results can lead to approximate solutions to the multiobjective H ₂/H _∞ problem together with tight estimates of the corresponding deviation from its optimal value.     

Asymptotic Fourier Coefficients for a C∞ Bell (Smoothed-“Top-Hat”) & the Fourier Extension Problem

In constructing local Fourier bases and in solving differential equations with nonperiodic solutions through Fourier spectral algorithms, it is necessary to solve the Fourier Extension Problem. This is the task of extending a nonperiodic function, defined on an interval , to a function which is periodic on the larger interval . We derive the asymptotic Fourier coefficients for an infinitely differentiable function which is one on an interval , identically zero for , and varies smoothly in between. Such smoothed “top-hat” functions are “bells” in wavelet theory. Our bell is (for x ≥ 0) where where . By applying steepest descents to approximate the coefficient integrals in the limit of large degree j, we show that when the width L is fixed, the Fourier cosine coefficients a _j of on are proportional to where Λ(j) is an oscillatory factor of degree given in the text. We also show that to minimize error in a Fourier series truncated after the Nth term, the width should be chosen to increase with N as . We derive similar asymptotics for the function f(x)=x as extended by a more sophisticated scheme with overlapping bells; this gives an even faster rate of Fourier convergence     

Robust H ∞ performance problem for linear systems with nonlinear uncertainties in all system matrices

This paper considers robust performance analysis and H X controller design for a class of systems with time-varying and nonlinear uncertainties. These uncertainties are allowed to exist not only in the state, but also in the control input, measurement output, exogenous input and derivative of state. A new sufficient condition based on LMI is first provided to analyse the robust H X performance problem of the free systems. For the general case, it is shown that a solvability condition for the output feedback control problem can be reduced to that of a set of LMIs with algebraic constraints. Then it is shown that in some cases, the constraints can be eliminated through simplifications and the output feedback controller design methods can be provided in terms of LMIs. In particular, two special cases of the systems with nonlinear uncertainties are discussed thoroughly and the design procedures of output feedback controllers are provided via typical LMIs. Furthermore, for a class of systems with both structured and nonlinear uncertainties, a new solvability condition is presented and the corresponding problem also cast into that of an auxiliary system without uncertainties. A few examples are also given to demonstrate the effectiveness of the proposed approaches.     

The general distance problem in H∞ optimal control theory

The general distance problem that arises in H∞ optimal control theory is considered. Transformations that reduce the general H∞ problem to the general distance problem are reviewed, and an iterative scheme called γ-iteration is considered, in which the general distance problem is reduced to a standard best approximation problem. The γ-iteration is viewed as a problem of finding the zero crossing of a function, This function is shown to be continuous, monotonically decreasing, convex and bounded by some very simple functions. These properties make it possible to obtain very rapid convergence of the iterative process. The issues of model-reduction and approximation in H∞-synthesis will also be addressed.     

A structure-preserving algorithm for the minimum H ∞ norm computation of finite-time state feedback control problem

The algorithm being developed here is based on the generating function approach for finite-time H _∞ control and application of canonical transformation of linear Hamiltonian system. First, an equivalent finite-time H _∞ control law in terms of the third-type generating function is derived. Then, by using symplectic structure of the Hamiltonian system's state transition matrix, a group of matrix recursive formulae are deduced for the evaluation of the finite-time H _∞ control law. Combining with a matrix singularity testing procedure, this recursive algorithm verifies the existence condition of sub-optimal H _∞ controllers and gives the minimum H _∞ norm of finite-time control systems. Inherited from the canonical transformation, the matrix recursive formulae have a standard symplectic form; this structure-preserving property helps facilitate reliable and effective computation. Numerical results show the effectiveness of the proposed algorithm.     

Coherent H∞Control for Linear Quantum Systems With Uncertainties in the Interaction Hamiltonian

This work conducts robust H^∞analysis for a class of quantum systems subject to perturbations in the interaction Hamiltonian.A necessary and sufficient condition for the robustly strict bounded real property of this type of uncertain quantum system is proposed.This paper focuses on the study of coherent robust H^∞controller design for quantum systems with uncertainties in the interaction Hamiltonian.The desired controller is connected with the uncertain quantum system through direct and indirect couplings.A necessary and sufficient condition is provided to build a connection between the robust H^∞control problem and the scaled H^∞control problem.A numerical procedure is provided to obtain coefficients of a coherent controller.An example is presented to illustrate the controller design method.     

Full order H ∞ filtering for linear systems in the frequency domain

This paper proposes an easier frequency domain solution to the standard H _∞ filtering problem using a polynomial approach. The design of the H _∞ filter in the frequency domain is first obtained from the time domain solution which is related to a Riccati equation, and then by the use of the connecting relationship between the time and frequency domain approach given by Hippe [8], its representation in the frequency domain is derived. The filter is easy to calculate as it requires the computation of a single gain and it is easily implementable also. A numerical example is given to illustrate the presented approach.     

HAPE3D—a new constructive algorithm for the 3D irregular packing problem

We propose a new constructive algorithm, called HAPE3 D, which is a heuristic algorithm based on the principle of minimum total potential energy for the 3D irregular packing problem, involving packing a set of irregularly shaped polyhedrons into a box-shaped container with fixed width and length but unconstrained height. The objective is to allocate all the polyhedrons in the container, and thus minimize the waste or maximize profit. HAPE3 D can deal with arbitrarily shaped polyhedrons, which can be rotated around each coordinate axis at different angles. The most outstanding merit is that HAPE3 D does not need to calculate no-fit polyhedron(NFP), which is a huge obstacle for the 3D packing problem. HAPE3 D can also be hybridized with a meta-heuristic algorithm such as simulated annealing. Two groups of computational experiments demonstrate the good performance of HAPE3 D and prove that it can be hybridized quite well with a meta-heuristic algorithm to further improve the packing quality.     

Local bifurcations in the periodic boundary value problem for the generalized Kuramoto–Sivashinsky equation

For a version of the generalized Kuramoto–Sivashinsky equation with “violated” symmetry, the periodic boundary value problem was investigated. For the given dynamic distributed-parameter system, consideration was given to the issue of local bifurcations at replacing stability by spatially homogeneous equilibrium states. In particular, the bifurcation of the two-dimensional local attractor with all Lyapunov-unstable solutions on it was detected. Analysis of the bifurcation problem relies on the method of the integral manifolds and normal forms for the systems with infinitely dimensional space of the initial conditions.     

L ∞ error bound for the phase matching approximation (the one-step-at-a-time Hankel norm model reduction version)

Parallel to what was done for the balanced model reduction version of the phase approximation problem (see Li and Jonckheere 1987), this paper provides an L ^∞ bound on the phase approximation error when one-step-at-a-time optimal Hankel norm model reduction is used to reduce the stable projection of the phase function matrix. The one-step-at-a-time Hankel norm procedure allows for an L ^∞ phase error bound twice as small as that of the balanced version.     

“Almost-stable” matchings in the Hospitals / Residents problem with Couples

The Hospitals / Residents problem with Couples (hrc) models the allocation of intending junior doctors to hospitals where couples are allowed to submit joint preference lists over pairs of (typically geographically close) hospitals. It is known that a stable matching need not exist, so we consider min bp hrc, the problem of finding a matching that admits the minimum number of blocking pairs (i.e., is “as stable as possible”). We show that this problem is NP-hard and difficult to approximate even in the highly restricted case that each couple finds only one hospital pair acceptable. However if we further assume that the preference list of each single resident and hospital is of length at most 2, we give a polynomial-time algorithm for this case. We then present the first Integer Programming (IP) and Constraint Programming (CP) models for min bp hrc. Finally, we discuss an empirical evaluation of these models applied to randomly-generated instances of min bp hrc. We find that on average, the CP model is about 1.15 times faster than the IP model, and when presolving is applied to the CP model, it is on average 8.14 times faster. We further observe that the number of blocking pairs admitted by a solution is very small, i.e., usually at most 1, and never more than 2, for the (28,000) instances considered.     

Diffusion chaos in the reaction–diffusion boundary problem in the dumbbell domain

We consider a boundary problem of the reaction–diffusion type in the domain that consists of two rectangular areas connected by a bridge. The bridge width is a bifurcation parameter of the problem and is changed in such way that the measure of the domain is preserved. The conditions on chaotic oscillations emergence have been studied and the dependence of invariant characteristics of the attractor on the bridge width has been constructed. The diffusion parameter has been chosen such that, in the case of widest possible bridge (corresponding to a rectangular domain), the spatially homogeneous cycle of the problem is orbitally asymptotically stable. By decreasing the bridge width, the homogeneous cycle loses stability; then, a spatially inhomogeneous chaotic attractor emerges. For the obtained attractor, we have calculated the Lyapunov exponents and Lyapunov dimension and observed that the dimension grows as the parameter decreases, but is bounded. We have shown that the dimension growth is connected with the growing complexity of the distribution of stable solutions with respect to the space variable.     

What is P3P? (the Platform for Privacy Preferences)

P3P promises protection against surreptitious data mining. Stephen Smith López explains its workings.     

Control design for the nonlinear benchmark problem via the output regulation method

The problem of designing a feedback controller to achieve asymptotic disturbance rejection / attenuation while maintaining good transient response in the RTAC system is known as a benchmark nonlinear control problem, which has been an intensive research subject since 1995. In this paper, we will further investigate the solvability of the robust disturbance rejection problem of the RTAC system by the measurement output feedback control based on the robust output regulation method. We have obtained a design by overcoming two major obstacles: find a closed-form solution of the regulator equations; and devise a nonlinear internal model to account for non-polynomial nonlinearities.