一类Birkhoff型2-周期三角和仿三角插值(英文)

本文讨论了2π周期和反周期函数在等距结点上的一类Birkhoff型2-周期三角和仿三角插值问题,给出了此问题有解的充要条件,并构造出插值基。     

一类Birkhoff型仿三角插值

本文讨论了2π反周期函数的一类Birkhoff型等距结点的仿三角插值问题,给出了此问题有解的充要条件,并构造出插值基。     

关于二元函数的三角插值逼近

本文以两组不同的节点构造了一个组合型的二元三角插值多项式算子Lmn(f;x,y),并且研究了二元连续周期函数对这个算子的收敛性及收敛阶的估计等问题。     

可调形三次三角Cardinal插值样条曲线

在三次Cardinal插值样条曲线的基础上,引入了三角函数多项式,得到一组带调形参数的三次三角Cardinal样条基函数,以此构造一种可调形的三次三角Cardinal插值样条曲线.该插值样条可以精确表示直线、圆弧、椭圆以及自由曲线,改变调形参数可以调控插值曲线的形状.该插值样条避免了使用有理形式,其表达式较为简洁,计算量也相对较少,从而为多种线段的构造与处理提供了一种通用与简便的方法.     

插值三角多项式在Orlicz空间逼近的渐进等式

对于具有等距分布插值结点的三角多项式,借助广义的Minkowski不等式在Orlicz空间内建立了由三角多项式逼近的渐近等式.并对于Orlicz空间内不同的函数类给出不同的结果.     

三角域上C~2连续的分片二元五次插值多项式

三角域上C~2连续的分片插值多项式在实际中有广泛的用途.若边界具有约束,上述多项式一般不低于9次,而5次多项式一般只能达到C~1连续.本文提出三角域上C~2连续的二元五次多项式存在的充要条件,并给出数值实例以显示如何运用本文结果来构造这类多项式.     

三角域上C~1插值的两种表示

在有限元计算中,散乱数据插值以及曲面设计和表示等问题常常需要构造三角域上C~1连续的分片插值多项式.Zenisek证明了闭三角域上整体具有m阶光滑的双变量插值多项式至少是4m+1次的.在实际问题中最常用到的是三角域上C~1连续五次双变量插值多项式的表示.     

二重三角插值多项式的求和因子法求和

选取一组求和因子ρａ,β构造了二重三角插值算子Ｆｍｎ（ｆ;ｙ）,使对于任意的ｆ（ｘ,ｙ）∈Ｃ２π,２π都能在全面上一致收敛,且达到最佳收敛阶。     

带重结点的三角求积公式的迭代构造

本文以三角多项式类作为工具讨论了偶数个结点情况下的带重结点的具有最大三角精度的三角求积公式,由拟正交三角多项式的性质给出了求积公式系数的迭代构造。     

新组合型的三角插值多项式

将被插函数进行组合平均,构造一个新组合型的三角插值多项式Cn(f;t,x),使得它在全轴上一致收敛到每个以2π为周期的连续函数,且对Cj2π连续函数类的逼近阶达到最佳,这里0jt,t为任给的奇自然数.     

Extremal Trigonometric and Power Polynomials in Several Variables

We study extremal nonnegative polynomials in several variables. Our approach makes substantial use of block Toeplitz matrices. Note that the blocks of these matrices are themselves Toeplitz matrices.     

求解混合三角多项式方程组的直接GBQ方法

许多科学与工程领域,我们经常需要求混合三角多项式方程组的全部解.一般来说,混合三角多项式方程组可以通过变量替换及增加二次多项式转化为多项式方程组,进而利用数值方法进行求解,但这种转化会增大问题的规模从而增加计算量.在本文中,我们不将问题转化,考虑利用直接同伦方法求解,并给出基于GBQ方法构造的初始方程组及同伦定理的证明.数值实验结果表明我们构造的直接同伦方法较已有的直接同伦方法更加有效.     

On the Decay of Infinite Products of Trigonometric Polynomials

We consider infinite products of the form f(=_k=1 m _k(2^-k), where {m _k} is an arbitrary sequence of trigonometric polynomials of degree at most n with uniformly bounded norms such that m _k(0)= 1 for all k. We show that f() can decrease at infinity not faster than O(^-n) and present conditions under which this maximal decay is attained. This result can be applied to the theory of nonstationary wavelets and nonstationary subdivision schemes. In particular, it restricts the smoothness of nonstationary wavelets by the length of their support. This also generalizes well-known similar results obtained for stable sequences of polynomials (when all m _k coincide). By means of several examples, we show that by weakening the boundedness conditions one can achieve exponential decay.     

A Sharpening of the Taikov Lower Bound in the Inequality between the C- and L-Norms for Trigonometric Polynomials

Mathematical Notes -     

Lacunary Interpolation by Antiperiodic Trigonometric Polynomials

The problem of lacunary trigonometric interpolation is investigated. Does a trigonometric polynomial T exist which satisfies T(x _k) = a _k, D ^m T(x _k) = b _k, 0 k n – 1, where x _k = k/n is a nodal set, a _k and b _k are prescribed complex numbers, and m N. Results obtained by several authors for the periodic case are extended to the antiperiodic case. In particular solvability is established when n as well as m are even. In this case a periodic solution does not exist.     

关于一类新的Bernstein型三角求和多项式

A new family of trigonometric summation polynomials, Gn,r(f;θ), of Bernstein type is constructed. In contrast to other trigonometric summation polynomials, the convergence properties of the new polynomials are superior to others. It is proved that Gn,r(f;θ) converges to arbitrary continuous functions with period 2π uniformly on (-∞, ∞) as n→∞. In particular, Gn,r(f;θ) has the best convergence order, and its saturation order is 1/n2r 4.     

On Polynomials over a Finite Field of Even Characteristic with Maximum Absolute Value of the Trigonometric Sum

We study trigonometric sums in finite fields . The Weil estimate of such sums is well known: , where f is a polynomial with coefficients from F(Q). We construct two classes of polynomials f, , for which attains the largest possible value and, in particular, .     

Trigonometric Convex Underestimator for the Base Functions in Fourier Space

A three-parameter (a, b, x_s) convex underestimator of the functional form (x) = -a sin[k(x-x_s)] + b for the function f(x) = sin(x+s), x [x_L, x_U], is presented. The proposed method is deterministic and guarantees the existence of at least one convex underestimator of this functional form. We show that, at small k, the method approaches an asymptotic solution. We show that the maximum separation distance of the underestimator from the minimum of the function grows linearly with the domain size. The method can be applied to trigonometric polynomial functions of arbitrary dimensionality and arbitrary degree. We illustrate the features of the new trigonometric underestimator with numerical examples.Support from the National Science Foundation and the National Institutes of Health Grant R01 GM52032 is gratefully acknowledged.