The use of fake algebraic Riccati equations for co-channel demodulation

This paper describes a method for nonlinear filtering based on an adaptive observer, which guarantees the local stability of the linearized error system. A fake algebraic Riccati equation is employed in the calculation of the filter gain. The design procedure attempts to produce a stable filter at the expense of optimality. This contrasts with the extended Kalman filter (EKF), which attempts to preserve optimality via its linearization procedure, at the expense of stability. A passivity approach is applied to deduce stability conditions for the filter error system. The performance is compared with an EKF for a co-channel frequency demodulation application.     

Choice of calibration equations in calibrating microwave test fixtures

The error theory of linear equation system has been applied to the calibration procedure of microwave network analyser in this article. A new explanation for the choice of the linear calibration equations is proposed and a general principle for choosing calibration equations is presented. The method can also be used to predict the occurrence of the problem of frequency limitation at some periodic frequencies. This principle is employed to the thru-short-delay (TSD) method and the solution using the chosen equations gives the most accurate results. A good agreement between the theory and the experiment has been obtained.     

Differential covariant formalism for solving Maxwell's equations incurvilinear coordinates: oblique scattering from lossy periodic surfaces

A rigorous differential method describing the diffraction properties of lossy periodic surfaces is presented. A nonorthogonal coordinate system and a covariant formalism of Maxwell's equation are used simplifying boundary conditions expression. Only one eigenvalue system, unique for the TE and TM polarizations even for an oblique incidence, needs to be solved. Thus the numerical treatment is very efficient and CPU requirements significantly reduced. Numerical results are successfully compared with those obtained by an integral method using the boundary element method (BEM) as a numerical procedure     

Levinson-like and Schur-like fast algorithms for solvingblock-slanted Toeplitz systems of equations arising in wavelet-basedsolution of integral equations

The Wiener-Hopf integral equation of linear least-squares estimation of a wide-sense stationary random process and the Krein integral equation of one-dimensional (1-D) inverse scattering are Fredholm equations with symmetric Toeplitz kernels. They are transformed using a wavelet-based Galerkin method into a symmetric “block-slanted Toeplitz (BST)” system of equations. Levinson-like and Schur-like fast algorithms are developed for solving the symmetric BST system of equations. The significance of these algorithms is as follows. If the kernel of the integral equation is not a Calderon-Zygmund operator, the wavelet transform may not sparsify it. The kernel of the Krein and Wiener-Hopf integral equations does not, in general, satisfy the Calderon-Zygmund conditions. As a result, application of the wavelet transform to the integral equation does not yield a sparse system matrix. There is, therefore, a need for fast algorithms that directly exploit the (symmetric block-slanted Toeplitz) structure of the system matrix and do not rely on sparsity. The first such O(n²) algorithms, viz., a Levinson-like algorithm and a Schur (1917) like algorithm, are presented. These algorithms are also applied to the factorization of the BST system matrix. The Levinson-like algorithm also yields a test for positive definiteness of the BST system matrix. The results obtained are directly applicable to the problem of constrained deconvolution of a nonstationary signal, where the locations of the smooth regions of the signal being deconvolved are known a priori     

Characteristic equations of optimal linear multivariable control systems

A simple derivation of the frequency-domain characteristic equation of the optimal linear multivariable control system is given. The equation is obtained from Pontryagin's maximum principle and is compared with alternative expressions given in the literature.     

Wiener filter design using polynomial equations

A simplified way of deriving realizable and explicit Wiener filters is presented. Discrete-time problems are discussed in a polynomial equation framework. Optimal filters, predictors, and smoothers are calculated by means of spectral factorizations and linear polynomial equations. A tool for obtaining these equations, for a given problem structure, is described. It is based on the evaluation of orthogonality in the frequency domain, by means of canceling stable poles with zeros. Comparisons are made to previously known derivation methodologies such as completing the squares for the polynomial systems approach and the classical Wiener solution. The simplicity of the proposed derivation method is particularly evident in multistage filtering problems. To illustrate, two examples are discussed: a filtering and a generalized deconvolution problem. A new solvability condition for linear polynomial equation appearing in scalar problems is also presented     

Fredholm resolvents, Wiener-Hopf equations, and Riccati differential equations

We shall show that the solution of Fredholm equations with symmetric kernels of a certain type can be reduced to the solution of a related Wiener-Hopf integral equation. A least-squares filtering problem is associated with this equation. When the kernel has a separable form, this related problem suggests that the solution can be obtained via a matrix Riccati differential equation, which may be a more convenient form for digital computer evaluation. The Fredholm determinant is also expressed in terms of the solution to the Riccati equation; this formula can also be used for the numerical determination of eigenvalues. The relations to similar work by Anderson and Moore and by Schumitzky are also discussed.     

Numerical solution of integral equations for dielectric objects ofprismatic shapes

A numerical method to investigate scattering from dielectric geometries of prismatic shapes has been developed. The surface integral equations are formulated by Schelkunoff's equivalence principle in terms of equivalent surface electric and magnetic currents. To solve these integral equations for the unknown currents, the object's cross-section is mapped onto a circle. In the transformed space, Fourier type entire-domain basis functions are used in the cross section and triangular subdomain basis functions are selected along the generating curve to represent the currents. A moment method is then used to reduce the integral equations to a matrix equation to compute the current coefficients. It is found that the transformation of the object's surface to a circular shape improves the convergence of the current mode in the cross-section. However, the current modes are coupled on the surface and the matrix equation includes all the modes     

Error characterization for the time-domain numerical solution ofMaxwell's equations

The accuracy and stability of transient numerical methods in electromagnetics is an important consideration, for which an analytical measure is necessary. Of the several approaches commonly used to indicate accuracy of numerical methods, the modified equation of Warming and Hyett [1974] is examined, for several finite-difference and finite-element time-domain methods. In the method of Warming and Hyett, a Taylor-series representation of each unknown is substituted into the difference equation and, through a rather lengthy series of algebraic steps, reduced to what is known as a modified equation. From this modified equation, which represents the actual differential equation being solved by the numerical method, the stability, and relative phase and magnitude accuracy, of the method can be ascertained. As a final introductory note, the one-dimensional equations for each of the algorithms are used in the development of the modified equation and the dispersion relations. The extension of each of the one-dimensional results to two and three dimensions is discussed, in the context of each method     

On the choice of expansion and weighting functions in the numerical solution of operator equations

One of the objectives of this paper is to discuss the mathematical requirements that the expansion functions must satisfy in the method of moments (MM) solution of an operator equation. A simple differential equation is solved to demonstrate these requirements. The second objective is to study the numerical stability of point matching method, Galerkin's method, and the method of least squares. Pocklington's integral equation is considered and numerical results are presented to illustrate the effect of various choices of weighting functions on the rate of convergence. Finally, it is shown that certain choices of expansion and weighting functions yield numerically acceptable results even though they are not admissible from a strictly mathematical point of view. The reason for this paradox is outlined.     

Efficient solution of eigenvalue equations of optical waveguidingstructures

A general numerical method is presented that is capable of extracting all the zeros of a complex equation. This method allows accurate determination of the complex propagation constants of general multilayer optical and microwave planar waveguides, the computation of energy states and their lifetimes of semiconductor heterostructures, and the roots of complex transcendental equations from other scientific disciplines. The method differs from previous approaches in that the time-consuming differentiation of the complex function is not required. Furthermore, the present method is not affected by the presence of complex poles and so can be used for the solution of meromorphic transcendental equations. In practice, the method is found to be much faster than other rigorous approaches     

Converting affine recurrence equations to quasi-uniform recurrence equations

Most work on the problem of synthesizing a systolic array from a system of recurrence equations is restricted to systems of uniform recurrence equations. Recently, researchers have begun to relax this restriction to include systems of affine recurrence equations. A system of uniform recurrence equations typically can be embedded in spacetime so that the distance between a variable and a dependent variable does not depend on the problem size. Systems of affine recurrence equations that are not uniform do not enjoy this property. A method is presented for converting a system of affine recurrence equations to an equivalent system of recurrence equations that is uniform, except for points near the boundaries of its index sets. Necessary and sufficient conditions are given for an affine system to be amenable to such a conversion, along with an algorithm that checks for these conditions, and a procedure that converts those affine systems which can be converted.The characterization of convertible systems brings together classical ideas in algebraic geometry, number theory, and matrix representations of groups. While the proof of this characterization is complex, the characterization itself is simple, suggesting that the mathematical ideas are well chosen for this difficult problem in array design.     

Current equations for velocity overshoot

A generalized current equation is presented for the operation of submicron devices by supplementing the drift and diffusion currents with gradient, rate and relaxation currents. The equation includes the most important features of velocity overshoot.     

基于对称约化的偏微分方程相似解研究

由于非线性系统的复杂性,对于其求解问题的研究目前还没有通用的方法,为了丰富非线性系统的求解方法,在此通过偏微分方程的决定方程确定点对称无穷小生成元,结合对称约化中的非经典Lie群法得到热方程新的相似解,并基于符号计算系统Maple给出相应的符号计算方法和实现步骤。结果表明,该算法能够有效求解PDEs的相似解,并且不需要显示地求解对应于不变曲面条件的特征方程,同时也适用于其他的发展方程。     

Fadeeva's algorithm for spatial dynamical equations

An algorithm is developed to compute the characteristic polynomial and the inverse of the system matrix of a spatial dynamical equation. Similar to the temporal case, the algorithm is computationally simpler than Cramer's rule.     

基于Toeplitz方程的改进广义预测PID控制

针对具有较大时滞的复杂被控对象,研究了改进的广义预测(GPC)PID控制算法。在保证经典PID控制性能的前提下,用滚动预测优化原理,自整定PID控制参数,同时解决系统时滞引起控制问题。通过最后对仿真结果的分析来看,运用Toeplitz方程的改进算法能有效提高系统的稳定性和求解计算的快速性。     

Semiconductor current-flow equations (diffusion and degeneracy)

The correct form for the current-flow equation in semiconductors in the presence of density and temperature gradients, as well as electric fields, is derived from a perturbation solution of Boltzmann's equation. The conditions under which the various widely used approximate forms of the current-flow equation are valid are clearly discussed. A new term that occurs if the relaxation time depends on position is derived, and is shown to be comparable in magnitude to the other terms in the current-flow equation.     

Wavelets and differential-dilation equations

It is shown how differential-dilation equations can be constructed using iterations, similar to the iterations with which wavelets and dilation equations are constructed. A continuous-time wavelet is constructed starting from a differential-dilation equation. It has compact support and excellent time domain and frequency domain localization properties. The wavelet is infinitely differentiable and therefore cannot be obtained using digital filter banks. In addition, the wavelet has excellent approximation properties. New sampling and differentiation techniques are also introduced. Results on image interpolation using the solution of the differential-dilation equation are presented. Examples are given, demonstrating the suitability of the new wavelet function for signal analysis     

两个非线性方程的势对称及其不变解

通过计算NTT方程和Burgers方程的势对称扩大了其古典对称,并获得了 Burgers 方程的一系列新的精确解. 首先,基于微分特征列集算法确定了NTT方程和Burgers方程的古典对称和势对称,并确定了 Burgers 方程的两个势对称对应的单参数Lie变换群. 其次,利用推广的简单方程方法构造了 Burgers方程的不变解,这些解分别以含任意两个参数的双曲函数、三角函数和有理函数表示. 最后,将势对称对应的Lie变换群(14)作用于Burgers方程的不变解上获得了新的精确解,重要的是这些解都不能由方程的古典对称得到.