非正规情形下代数Hermite-Pade逼近的存在性与唯一性

本文研究了非正规情形下一局部解析函数ｆ（ｚ）的代数Ｈｅｒｍｉｔｅ－Ｐａｄé逼近,并在一般条件下证明了它的存在性与唯一性     

最佳L2局部逼近存在唯一的充分必要条件

本文给出了最佳Ｌ２局部逼近的存在唯一性定理，设ｆ∈Ｌ２（０，δ），Ｓｎ＝ｓｐａｎ（ｕ０，ｕ１，．．．Ｕｎ－１）Ｃ＾ｎ－１（０，δ），且ｄｅｔＷｎ（ｕ０，ｕ１，．．．ｕｎ－１；０）≠０，那么，当ｘ→０时，网（Ｐｘ（ｆ，Ｓｎ）收敛于Ｓｎ中某元素Ｐ０（ｆ，Ｓｎ）的充要条件为：ｆ＝Ｐｎ－１＋ｈ，其中Ｐｎ－１（ｔ）＝ｎ－１∑ｉ＝１ａｉｔｉ（ｈ，１）ｘ＝０（Ｘ＾ｎ），ｘ→０，且Ｐ０（ｆ，Ｓｎ）＝ＵＷ＾－１ｎＡ     

关于一类函数的代数逼近度的注记

设A（z)是函数列{fn(z)}的极限函数，已知^[4],当|fn(z)-A(z)|在z=0的阶满足一定的条件时，A（z)是超越函数。本文给出了极限函数的代数逼近度函数。     

几种有理插值函数的逼近性质

1　引　　言在曲线和曲面设计中,样条插值是有用的和强有力的工具.不少作者已经研究了很多种类型的样条插值[1,2,3,4].近些年来,有理插值样条,特别是三次有理插值样条,以及它们在外型控制中的应用,已有了不少工作[5,6,7].有理插值样条的表达式中有某些参数,正是由于这些参数,有理插值样条在外型控制中充分显示了它的灵活性;但也正是由于这些参数,使它的逼近性质的研究增加了困难.因此,关于有理插值样条的逼近性质的研究很少见诸文献.本文在第二节首先叙述几种典型的有理插值样条,其中包括分母为一次、二次的三次有理插值样条和仅基于函数值…     

保凸性的代数多项式在L中的逼近

设f(x)∈L[-1,1].以∏_n表示阶不超过n的代数多项式的全体.我们已经熟知∏_n关于f(x)在L中的最佳逼近E_(f)_L可以用它的L中的k阶光滑模w_k(f,1/n)_L来刻划的事实:但是,当被逼近的函数f(x)是凸函数时,如果我们限制去逼近的代数多项式也是凸的,那么对于相应的逼近度能得到什么样的估计呢?以∏_n~*表示∏_n中的所有凸的多项式的全体.     

一类指数型整函数插值算子的逼近性质(2)

本文研究了一类指数型整函数插值算子在C（R）和Lp(1≤p≤∞）空间上的饱和性质。     

函数的存在性问题

存在性问题历来是竞赛命题的重要内容 ,函数中的存在性问题也占有一定比重 ,笔者将其解法介绍如下 .函数中的存在性问题主要有三种类型 ,即肯定型、否定型和探索型 .分述如下 .1　肯定型　已知函数满足某些条件 ,证明某种对象一定存在 ,常见的有如下方法 .例 1　 (第 2 9届ＩＭＯ国家集训班选拔考试试题 )设ｆ(ｘ) =3ｘ 2 ,证明 :存在正整数ｍ使得ｆ( 10 0 ) (ｍ)能被 1 988整除 .证　ｆ( 10 0 ) (ｍ) =2 3× 2 3 2 × 2 … 3 99× 2 3 10 0 ×ｍ .因 3与 1 988互质 ,3 10 0 与 1 988也互质 .由裴蜀 (Ｂｅ′ｚｏｕｔ)恒等式 ,存在自然…     

高维代数多项式逼近与a.e.逼近的一些结果

自Korovkin的文[1]问世以来,有关线性正算子逼近的各种工作一直是颇受逼近论界关注的研究课题,如[2]～[4]等分别考虑了连续函数,L~p空间及随机函数的正算子逼近.然而在一元逼近中,由积分核引出的卷积与形式卷积型算子却占有极为重要的地位,这不仅因为已经有较多具体的积分核能方便地用于误差估计;特别,还有一些如Timan定理那样     

The Existence and Local Behavior of Multivariate Algebraic Function Approximations

The existing scheme of rational polynomial approximants, defined by multivariate power series, is extended to define approximants with branch points. The existence theorem is obtained. The basic properties used to define the rational approximants can be preserved almost intactly. Especially, the local behavior of the     

二元二次函数逼近的存在性和局部性

This paper analysis the local behavior of the bivariate quadratic function approximation to a bivariate function which has a given power series expansion about the origin. It is shown that the bivariate quadratic Hermite-Pade form always defines a bivariate quadratic function and that this function is analytic in a neighborhood of the origin.     

Good Local Behavior of Offsets to Implicit Algebraic Curves

The notion of good local behavior of an offset curve was introduced in [2,4] to denote that the behavior of an offset was locally good from a topological point of view. Also, in these papers the problem of checking whether good local behavior holds for a particular offsetting distance, and of computing intervals of distances with this nice property, was addressed for the case of rational algebraic curves. Thus, here we generalize the results and techniques of these papers to the case when the curve to work with is an implicitly given, possibly singular, non-necessarily rational algebraic curve. Furthermore, a generalization of the (already known) results relating offsets and evolutes of regularly parametrized curves, is presented for the case of possibly singular, implicit algebraic curves.     

Piecewise Rational Approximations of Real Algebraic Curves

1.IntroductionAnaJgebraicplanecurveCofdegreedinn2isimplicitlydefinedbyasinglepolynomialequationf(x,y)=Oofdegreedwithcoefficientsinn.Arationalalgebraiccurveofdegreedinn2canadditionaJlybedefinedbyrationalparametricequationswhicharegivenas(x=G1(u),y=G2(u)),whereG1andG2arerationalfunctionsinuofdegreed,i.e-,eachisaquotientofpolynomiaJ8inuofmtalmumdegreedwithcoefficientsinn.ffetionalcurvesaxeonlyasubsetofimplicitalgebraiccurvesofdegreed+1.Whi1eaJldegreetwocurves(conics)arerational,oIilyasubsetof…     

Integral Representations and Approximations for Multivariate Gamma Distributions

Let R be a p×p-correlation matrix with an “m-factorial” inverse R ⁻¹ = D − BB′ with diagonal D minimizing the rank m of B. A new -variate integral representation is given for p-variate gamma distributions belonging to R, which is based on the above decomposition of R ⁻¹ without the restriction D > 0 required in former formulas. This extends the applicability of formulas with small m. For example, every p-variate gamma cdf can be computed by an at most -variate integral if p = 3 or p = 4. Since computation is only feasible for small m, a given R is approximated by an m-factorial R ₀. The cdf belonging to R is approximated by the cdf associated with R ₀ and some additional correction terms with the deviations between R and R ₀.     

一类函数增量的局部渐近性质

文章研究了一类函数增量的局部渐近性质,发现这类函数增量的局部渐近性对于一元实函数,二元及多元实函数,向量值函数和复函数在一定条件下都会保持不变,进而提出了两个相关的猜想:此类函数增量的渐近性是关于函数变换的拓扑不变量。     

On the Poles of Igusa's Local Zeta Function for Algebraic Sets

Let K be a p-adic field, let Z (s, f), sC, with Re(s) > 0,be the Igusa local zeta function associated to f(x) = (f₁(x),..., f_l(x)) [K (x₁, ..., x_n)]^l, and let be a Schwartz–Bruhatfunction. The aim of this paper is to describe explicitly thepoles of the meromorphic continuation of Z (s, f). Using resolutionof singularities it is possible to express Z (s, f) as a finitesum of p-adic monomial integrals. These monomial integrals arecomputed explicitly by using techniques of toroidal geometry.In this way, an explicit list of the candidates for poles ofZ (s, f) is obtained. 2000 Mathematics Subject Classification11S40, 14M25, 11D79.     

Algebraic Multigrid Preconditioners for Sparse Approximations of Boundary Element Matrices

This paper presents new algebraic multigrid preconditioners for sparse representations of boundary element matrices which arise from the so‐called adaptive‐cross‐approximation to dense boundary element matrices resulting from the standard collocation, or Galerkin boundary element discretization of the single layer potential operator.     

Existence of Multivariate Max-Universal Laws

If suitably normalized maxima of an i.i.d. sample converge in distribution, the limiting distribution is known to be max-infinitely divisible and the common distribution of the sample is said to belong to its domain of attraction. We prove the existence of max-universal distributions belonging to the domain of attraction of every max-infinitely divisible law. The proof follows in the spirit of corresponding results for normalized sums of i.i.d. random variables originated by Doeblin and shows that necessarily the sampling size has to be rapidly increasing. Restricting the growth rate of the sampling size, we prove that one necessarily deals with max-semistable distributions and their domains of attraction. 2000 Mathematics subject classification Primary—60G70 Secondary—60E99, 60F05