一种四次有理插值样条及其逼近性质

1引言有理样条函数是多项式样条函数的一种自然推广,但由于有理样条空间的复杂性,所以有关它的研究成果不象多项式样条那样完美,许多问题还值得进一步的研究．近几十年来,有理插值样条,特别是有理三次有理插值样条,由于它们在曲线曲面设计中的应用,已有许多学者进行了深入研究,取得了一系列的成果(见[1]-[7])．但四次有理插值样条由于其构造所花费的计算量太大以及在使用上很不方便而让人们忽视了其重要的应用价值,因此很少有人研究他们．实际上,在某些情况下四次有理插值样条有其独特的应用效果,如文[8]建立的一种具有局部插值性质的分母为二次的四次有理样条,即一个剖分     

样条型矩阵有理插值

The matrix valued rational interpolation is very useful in the partial realization problem and model reduction for all the linear system theory. Lagrange basic functions have been used in matrix valued rational interpolation. In this paper, according to the property of cardinal spline interpolation, we constructed a kind of spline type matrix valued rational interpolation, which based on cardinal spline. This spline type interpolation can avoid instability of high order polynomial interpolation and we obtained a useful formula.     

特殊形式的多元有理样条插值

有理样条插值问题最早是由R.Schaback提出的,由于R.Schaback考虑此问题时涉及到了非线性方程组的求解,因而实现起来比较复杂.后来,王仁宏等研究了几类特殊形式的插值有理样条函数,避开了求解非线性方程的困难.能否在多元情形下建立类似的结果?本文对此作出了肯定的回答,并就二元情形的三角剖分和四边形剖分建立了几类特殊形式的插值多元有理样条,构造性地证明了解的存在性和唯一性.     

广义有理样条的几种构造方法

本文利用Ｔｈｉｅｌｅ倒差分方法、Ｐａｄｅ逼近方法、广义Ｑ．Ｄ．算法及ε－算法等构造了几种广义有理样条函数．此外，通过直接法构造了（ｋ－１，ｋ）－型广义有理样条，给出了它的行列式表示和余项表示并证明了广义有理样条算子的存在性、唯一性、齐次性及连续性．     

三维空间中的有理样条插值

对三维空间某个多面体区域的四面体剖分，通过在每个四面体胞腔的棱和顶点设置适当的插值结点．本文给出了（１，１）型Ｃ⁰及Ｃ¹光滑的非奇异有理样条存在的充分必要条件．     

一类有理交错样条曲线的逼近性及形状修改

本文提出一类Ｃ＾２连续的四阶有理交错样条曲线，它能整体或局部逼近于控制多边形。     

研究多元样条的逐次分解法

本文在协调方程的基础上提出了研究多元样条的逐次分解法，并由此明了多元样条（包括多项式样条、有理样条乃至更一般的样条）在本质上是一个积分微分方和组的解。该方法具有以下优点：１）即可研究多项式样条，又可以研究有理样条乃至更一般的样条；２）即适用于三角剖分，双适用于直线剖分乃至更一般的代数曲线剖分；３）即能用于研究样条空间，又能用于研究样条环；４）可使许多问题局部化。     

有理B样条曲线的光顺拟合法

研究了用三次均匀有理Ｂ样条样曲线光顺拟合一组平面点列的问题,其中光顺性由曲线的能量积分与扰动的权平均来确定。     

一类预给极点的有理样条的构造

构造了一类特殊的有理样条,给出其表现公式及唯一性证明,并通过实例说明其优越性.     

一类基于l1模的最佳二次样条插值

本文讨论了二次样条插值的定解条件,在l_1模意义下给出了一类最佳二次样条插值的概念,以及寻找最佳二次样条插值的定解条件的方法.最后讨论了误差估计问题,并给出了实际算例.     

封闭曲线上的奇异积分方程的样条间接逼近解法

利用复插值样条函数，给出了定义于光滑封闭曲线上一般的正则型奇异积分方程的样条间接逼近解法，证明了一致收敛性．对于其中的一类奇异积分方程，还给出了近似解和误差估计．     

Exponential Box-Like Splines on Nonuniform Grids

We generalize the exponential box spline by allowing it to have arbitrarily spaced knots in any of its directions and derive the corresponding recurrence and differentiation rules. The corresponding spline space is spanned by the shifts of finitely many such splines and contains the usual family of exponential polynomials. The (local) linear independence of the spanning set is equivalent to a geometric condition closely related to unimodularity. January 10, 1996. Date revised: December 9, 1997. Date accepted: March 18, 1998.     

Penalized Estimation of Free-Knot Splines

Abstract

Polynomial splines are often used in statistical regression models for smooth response functions. When the number and location of the knots are optimized, the approximating power of the spline is improved and the model is nonparametric with locally determined smoothness. However, finding the optimal knot locations is an historically difficult problem. We present a new estimation approach that improves computational properties by penalizing coalescing knots. The resulting estimator is easier to compute than the unpenalized estimates of knot positions, eliminates unnecessary “corners” in the fitted curve, and in simulation studies, shows no increase in the loss. A number of GCV and AIC type criteria for choosing the number of knots are evaluated via simulation.     

Splines and Linear Control Theory

In this work, the relationship between splines and the linear control theory has been analyzed. We show that spline functions can be constructed naturally from the control theory. By establishing a framework based on control theory, we provide a simple and systematic way to construct splines. We have constructed the traditional spline functions including polynomial splines and the classical exponential spline. We have also discovered some new spline functions such as the combination of polynomial, exponential and trigonometric splines. The method proposed in this paper is easy to implement. Some numerical experiments are performed to investigate properties of different spline approximations.     

Martensen Splines

This paper is concerned with the construction of the fundamental functions associated with a two-point Hermite spline interpolation scheme used by Martensen in the context of the remainder of the Gregory quadrature rule. We derive both a recursive construction and an explicit representation in terms of the underlying B-Splines which can easily be deduced using Marsden’s identity. We can make use of these functions in order to introduce a local interpolation scheme which reproduces all splines. Finally, we examine the error of this interpolant to a sufficiently smooth function and realize that it behaves like in the case of splines of degree n. AMS subject classification (2000) 65D05, 65D07, 41A15     

Least Squares Solution of Bivariate Surface Fitting Problems Using Tensor Product Splines

The paper treats bivariate surface fitting problems, where the data points lie on lines parallel to one of the axes. The associated bivariate collocation matrix is investigated as a block Kronecker product of univariate collocation matrices. Based on various properties of this block Kronecker product, such scattered data are characterized where the associated interpolation problem using tensor product splines admits a unique solution.     

二元线性样条函数插值

二元样条函数插值在计算几何与计算机辅助几何设计中有着重要的作用.本文给出了一种矩形剖分上二元线性样条函数进行Lagrange插值时插值适定结点组所满足的拓扑与几何性质,这种性质依赖于二元线性样条函数所决定的分片线性代数曲线.     

On the Characterization of Quadratic Splines

A quadratic spline is a differentiable piecewise quadratic function. Many problems in the numerical analysis and optimization literature can be reformulated as unconstrained minimizations of quadratic splines. However, only special cases of quadratic splines have been studied in the existing literature and algorithms have been developed on a case-by-case basis. There lacks an analytical representation of a general or even convex quadratic spline. The current paper fills this gap by providing an analytical representation of a general quadratic spline. Furthermore, for a convex quadratic spline, it is shown that the representation can be refined in the neighborhood of a nondegenerate point and a set of nondegenerate minimizers. Based on these characterizations, many existing algorithms for specific convex quadratic splines are also finitely convergent for a general convex quadratic spline. Finally, we study the relationship between the convexity of a quadratic spline function and the monotonicity of the corresponding linear complementarity problem. It is shown that, although both conditions lead to easy solvability of the problem, they are different in general.This project was initiated when the first author was visiting the Technical University of Denmark and Erasmus University. The visit was partially funded by the Danish Natural Science Research Council.     

Error Estimates for Multilevel Approximation Using Polyharmonic Splines

Polyharmonic splines are used to interpolate data in a stationary multilevel iterative refinement scheme. By using such functions the necessary tools are provided to obtain simple pointwise error bounds on the approximation. Linear convergence between levels is shown for regular data on a scaled multiinteger grid, and a multilevel domain decomposition method.     

关于广义逆的向量连分式插值样条

本文首次引入了关于广义逆的向量有理插值样条的概念．这类插值样条具有Thiele型连分式的截断分式的表现形式．在它的构造过程中,不必用到连分式的三项递推关系,本文得到的新的有效的系数算法具有递推运算的特点．存在性的一个充分条件得以建立．包括唯一性在内的有关插值问题的某些结果得到证明．最后,本文给出了一个精确的插值误差公式．