Direct and Inverse Estimates for Bernstein Polynomials

Direct estimates for the Bernstein operator are presented by the Ditzian—Totik modulus of smoothness , whereby the step-weight φ is a function such that φ ² is concave. The inverse direction will be established for those step-weights φ for which φ ² and , are concave functions. This combines the classical estimate (φ=1 ) and the estimate developed by Ditzian and Totik ( ). In particular, the cases , λ∈[0,1] , are included. August 2, 1996. Date revised: March 28, 1997.     

Application of Quasihomogeneous Polynomials to Some Stability Problems

The quasihomogeneous polynomials examined previously by the author, especially quasiquadratic forms [1, 2], are used to study some stability problems. The stability of systems of differential equations with quasihomogeneous right-hand sides is studied. Theorems analogous to the first-approximation Lyapunov stability theorems are derived for one class of essentially nonlinear systems of a special form. Several problems for these systems are examined that may be among the critical cases for these nonlinear systems of differential equations.     

On Some Inverse Problems for First Order Operator-Differential Equations

Siberian Mathematical Journal - We study solvability of the inverse problems of recovering an unknown function on the nonlinear right-hand side of a first order operator-differential equation in...     

Co-Hopfian Modules of Generalized Inverse Polynomials

Let R be an associative ring not necessarily possessing an identity and (S, ≤) a strictly totally ordered monoid which is also artinian and satisfies that 0 ≤s for any s∈S. Assume that M is a left R-module having propertiy (F). It is shown that M is a co-Hopfian left R-module if and only if [M ^{S , ≤}] is a co-Hopfian left [[R ^{S , ≤}]]-module. Received October 14, 1998, Accepted October 15, 1999     

Explicit Formulae for Some Kazhdan-Lusztig Polynomials

We consider the Kazhdan-Lusztig polynomials P _u,v (q) indexed by permutations u, v having particular forms with regard to their monotonicity patterns. The main results are the following. First we obtain a simplified recurrence relation satisfied by P _u,v (q) when the maximum value of v S_n occurs in position n – 2 or n – 1. As a corollary we obtain the explicit expression for P_{e,3 4 ... n 1 2}(q) (where e denotes the identity permutation), as a q-analogue of the Fibonacci number. This establishes a conjecture due to M. Haiman. Second, we obtain an explicit expression for P_{e, 3 4 ... (n – 2) n (n – 1) 1 2}(q). Our proofs rely on the recurrence relation satisfied by the Kazhdan-Lusztig polynomials when the indexing permutations are of the form under consideration, and on the fact that these classes of permutations lend themselves to the use of induction. We present several conjectures regarding the expression for P _u,v (q) under hypotheses similar to those of the main results.     

Minimization of Energy Functionals Applied to Some Inverse Problems

We consider a general class of problems of the minimization of convex integral functionals subject to linear constraints. Using Fenchel duality, we prove the equality of the values of the minimization problem and its associated dual problem. This equality is a variational criterion for the existence of a solution to a large class of inverse problems entering the class of generalized Fredholm integral equations. In particular, our abstract results are applied to marginal problems for stochastic processes. Such problems naturally arise from the probabilistic approaches to quantum mechanics. Accepted 26 March 2001. Online publication 19 July 2001.     

Boundary Value and Inverse Problems for Some Classes of Nonclassical Operator-Differential Equations

We consider the solvability of boundary valueproblems and some inverse problems for operator-differentialequations of odd order which can be referred to as mixed typeequations since the coefficient of the higher order time derivative can change sign.Studying the general classes of boundary value problems with nonlocal boundary conditions,we establish the existence and uniqueness theorems of regular solutions under some conditions on data.

     

Inverse Problems for Parabolic Equations

The determination of variable filtration through a layer is an important and actual problem in filtration theory. This problem has been examined in some particular cases, for instance in the papers [1, 2].     

Algorithms for Inverse Eigenvalue Problems

Two new algorithms based on QR decompositions (QRDs) (with column pivoting) are proposed for solving inverse eigenvalue problems, and under some non-singularity assumptions they are both locally quadratically convergent. Several numerical tests are presented to illustrate their convergence behavior.     

Some Basic Lommel Polynomials

The basic Lommel polynomials associated to the₁₁q-Bessel function and the Jacksonq-Bessel functions are considered as orthogonal polynomials inq^ν, whereνis the order of the corresponding basic Bessel functions. The corresponding moment problems are both indeterminate and determinate depending on a parameter. Using techniques of Chihara and Maki we derive an explicit orthogonality measure, which is discrete and unbounded. For the indeterminate moment problem this measure is N-extremal. Some results on the zeros of the basic Bessel functions, both as functions of the order and of the argument are obtained. Precise asymptotic behaviour of the zeros of the₁₁q-Bessel function is obtained.     

Inverse Relations and the Products of Bernoulli Polynomials

In this paper, we give two inverse pairs of identities involving products of the Bernoulli polynomials and the Bernoulli polynomials of the second kind.     

Some Generating Functions for the Generalized Bessel Polynomials

The authors begin by presenting a systematic (historical) account of some linear generating functions for the generalized Bessel polynomials. It is then shown how these linear generating functions can be applied with a view to obtaining various new families of bilinear, bilateral, or mixed multilateral generating functions for the generalized Bessel polynomials. Some interesting generalizations of these classes of generating functions, involving hypergeometric functions, are also considered.     

On Inverse Problems for Semiconductor Equations

This paper is devoted to the investigation of inverse problems related to stationary drift-diffusion equations modeling semiconductor devices. In this context we analyze several identification problems corresponding to different types of measurements, where the parameter to be reconstructed is an inhomogeneity in the PDE model (doping profile). For a particular type of measurement (related to the voltage-current map) we consider special cases of drift-diffusion equations, where the inverse problems reduces to a classical inverse conductivity problem. A numerical experiment is presented for one of these special situations (linearized unipolar case).Lecture held by P.A. Markowich in the Seminario Matematico e Fisico on April 5, 2004Received: June, 2004     

两个反问题的数学模型

本文考察了两个工业中的反问题 ,讨论了如何建立起这些问题的偏微分方程模型 ,并最终归结为变分问题 ,简述了这些模型的求解方法 .     

Some Integral Mean Estimates for Polynomials with Restricted Zeros

Let P(z) be a polynomial of degree n having all its zeros in |z| ≤ k. Fork = 1,it is known that for each r 0 and |α|≥ 1,n(|α|- 1) {∫2π0|P(eiθ)|rdθ}1/r 0r≤ {∫2π0|1+ eiθ|rdθ}1/rmax|z|=|Dα P(z)|.In this paper, we shall first consider the case when k ≥ 1 and present certain generalizations of this inequality. Also for k ≤ 1, we shall prove an interesting result for Lacunary type of polynomials from which many results can be easily deduced.     

球面Jackson多项式逼近的正逆定理

研究了球而Jackson多项式Jv,sf的逼近阶,建立立该多项式逼近的强型正向与逆向不等式.利用球面光滑模较好地刻画了Jackson多项式的逼近性能,证明了存在与v和f无关的常数C1和C2,使得对于定义在球面上任意p-幂勒贝格可积或连续函数f成立C1ω(f,1/v)p≤‖Jv,sf-f‖p≤C2ω(f,1/v)p,其中ω(f,t)p是f的光滑模.     

Some Inequalities for Derivatives of Trigonometric and Algebraic Polynomials

We investigate inequalities for derivatives of trigonometric and algebraic polynomials in weighted L ^P spaces with weights satisfying the Muckenhoupt A _p condition. The proofs are based on an identity of Balázs and Kilgore [1] for derivatives of trigonometric polynomials. Also an inequality of Brudnyi in terms of rth order moduli of continuity ω_r will be given. We are able to give values to the constants in the inequalities.     

Some Results Concerning Growth of Polynomials

Let P(z) be a polynomial of degree n having no zeros in |z|< 1, then for every real or complex number β with |β|≤ 1, and |z|=1, R ≥ 1, it is proved by Dewan et al. [4] that ︱P(Rz)+ β( R+1/2 )n P(z)︱≤ 1 /2 { (︱Rn + β(R+1/2 )n︱+︱1+ β (R + 1 /2 )n︱) max |z|=1 |P(z)︱-(︱Rn + β (R+1/2 )n︱-︱1+ β(R+1/2 )n︱) min|z|=1 |P(z)︱}.In this paper we generalize the above inequality for polynomials having no zeros in |z|相似文献   

Some Combinatorial Properties of Schubert Polynomials

Schubert polynomials were introduced by Bernstein et al. and Demazure, and were extensively developed by Lascoux, Schützenberger, Macdonald, and others. We give an explicit combinatorial interpretation of the Schubert polynomial in terms of the reduced decompositions of the permutation w. Using this result, a variation of Schensted's correspondence due to Edelman and Greene allows one to associate in a natural way a certain set of tableaux with w, each tableau contributing a single term to . This correspondence leads to many problems and conjectures, whose interrelation is investigated. In Section 2 we consider permutations with no decreasing subsequence of length three (or 321-avoiding permutations). We show for such permutations that is a flag skew Schur function. In Section 3 we use this result to obtain some interesting properties of the rational function , where denotes a skew Schur function.Sara C. Billey: Supported by the National Physical Science Consortium. William Jockusch: Supported by an NSF Graduate Fellowship. Richard P. Stanley: Partially supported by NSF grants DMS-8901834 and DMS-9206374