基于NURBS的极小曲面造型

1 引言极小曲面问题是微分几何领域中一个古老而活跃的问题．在微分几何学中,极小曲面的研究已十分成熟．如何把极小曲面引入CAGD领域,是一个极有价值的课题．文献 [1]提出一种几何构造法,得到了一类三次多项式形式的负高斯曲率极小曲面,将其表示为三次B-B曲面,并将其用到房顶曲面设计当中．文献[2]讨论参数多项式极小曲面,证明了只存在一类三次等温参数极小曲面,并研究了这类曲面的一些基本性质．虽然这些多     

拟-?-渐近非扩张映像的修改的Halpern-Mann-型迭代的强收敛定理及应用

该文的目的是修改拟-φ-渐近非扩张映像的Halpern-Mann-型迭代算法.并证明,仅在一极限条件下,该迭代算法在Banach空间的框架下具有强收敛性.结果改进和推广了文献[4,6-7,11-13]以及其他一些人的最新结果.     

提高曲面拟合精度的最佳扰动算法

本文对[1]中的迭代算法提出了一个改进。改进的算法对于n个基函数的最小二乘拟合问题,最多扰动计算n次即可达到至少有n+1个最大拟合误差降到一致的结果。在许多情况下,这也是该问题的离散切比雪夫解。     

高维分形函数与插值

1 预备知识 1986年,Barnsley[1]采用某种特殊的迭代函数系统(IFS)构造了分形插值函数(FIF), 在计算机图形学等领域得到了广泛的应用(参见[1,2,5,6])．Massopust[4],J．S．Geronimo和 D．P．Hardin[3]等构造了三角形域上的自仿射分形函数,其图像称为分形曲面。文献[7]发现了矩形区域上分形函数的特征定理,并由此解决了矩形区域的分形插值问题．本文中     

无单调性集值变分不等式的一种投影算法

本文给出了求解无单调性集值变分不等式的一个新的投影算法，该算法所产生的迭代序列在Minty变分不等式解集非空且映射满足一定的连续性条件下收敛到解.对比文献[10]中的算法，本文中的算法使用了不同的线性搜索和半空间，在计算本文所引的两个数值例子时，该算法比文献[10]中的算法所需迭代步更少.     

一类广义非线性混合拟变分包含组

本文引入了一类新的带松弛单调映射和松弛Lipschitz映射的广义非线性混合拟变分包含组 ,构造了求解该类变分包含组的迭代算法 ,证明了该类变分包含组解的存在性以及由本文构造的迭代算法产生的迭代序列的强收敛性 .所得结果推广和改进了大量文献中的最新结果[1 5 ] .     

X(O8)=1且有亏格贰曲线束的一般型曲面(Ⅲ)

这一系列论文将给出x(O₅)=1且有亏格贰曲线束的一般型曲面的分类及例子。本文将给出一批新的有亏格贰曲线束的数值Campedelli曲面(定理1,2)。从历史上看,属于这范围的例子仅有文献[1]及文献[2]中两批。     

一类BZIER型的三角多项式曲线

1引言Bézier方法和B样条方法是表示与设计自由曲线曲面造型的主要方法[2][7],然而它不能描述除抛物线以外的圆锥曲线,NURBS方法虽然可以解决上述问题,但其权因子与参数化问题至今仍没有完全解决[2][7].另一方面,在飞机外形设计与数控加工中经常遇到许多由二次曲线弧等表示的形状,此时一些非多项式类型的曲线曲面造型方法显示了强大的威力[1][3][6][8].文献[4][5]给出了B样条形式和带形状参数的Bézier形式的三角多项式曲线,可以     

一类迭代系统解的存在性与唯一性

1986年张伟年在文献[1]中研究了迭代方程: sum from i=1 to n(λ_i f~i(x)=F(x)(f~0(x)=x,f~k(x)=f·f~(k-1)(x)) (*)解的存在性与唯一性,推广了文献[2]—[4]中的结果。本文将作进一步的推广。我们考察了一类具有相当广泛性的迭代系统:     

高阶C-B样条曲线曲面的显式形式

1引言基于多项式空间span{1,t,t~2,…,t~k}的B样条和Bézier曲线(面)是构造自由曲线、曲面强有力的工具,但是它们不能精确表示圆弧、椭圆等,也不能精确地表示正弦曲线和二次曲面,于是文献[1]提出了一种新的三次曲线(面)模型,称为C曲线(面),它们是低次多项式样条曲线(面)的拓广,具有很多B样条的良好性质,如对称性、保凸性等,不仅能精确表示二次曲线和曲面和某些超越曲线,而且克服了NURBS求导求积复杂的困难,因此引起了国内外广泛的关注,近年来涌现了大量的文献.文[5]将其三次C-B样条推广到了高阶的情形,给出了任意阶C-B样条曲线(面)的积分递推公式,并发展了许多诸     

A multivariate QD-like algorithm

The problem of constructing a univariate rational interpolant or Padé approximant for given data can be solved in various equivalent ways: one can compute the explicit solution of the system of interpolation or approximation conditions, or one can start a recursive algorithm, or one can obtain the rational function as the convergent of an interpolating or corresponding continued fraction.In case of multivariate functions general order systems of interpolation conditions for a multivariate rational interpolant and general order systems of approximation conditions for a multivariate Padé approximant were respectively solved in [6] and [9]. Equivalent recursive computation schemes were given in [3] for the rational interpolation case and in [5] for the Padé approximation case. At that moment we stated that the next step was to write the general order rational interpolants and Padé approximants as the convergent of a multivariate continued fraction so that the univariate equivalence of the three main defining techniques was also established for the multivariate case: algebraic relations, recurrence relations, continued fractions. In this paper a multivariate qd-like algorithm is developed that serves this purpose.     

Iterative polynomial interpolation and data compression

In this paper we look at some iterative interpolation schemes and investigate how they may be used in data compression. In particular, we use the pointwise polynomial interpolation method to decompose discrete data into a sequence of difference vectors. By compressing these differences, one can store an approximation to the data within a specified tolerance using a fraction of the original storage space (the larger the tolerance, the smaller the fraction).We review the iterative interpolation scheme, describe the decomposition algorithm and present some numerical examples. The numerical results are that the best compression rate (ratio of non-zero data in the approximation to the data in the original) is often attained by using cubic polynomials and in some cases polynomials of higher degree.This work was supported by The Royal Norwegian Council for Scientific and Industrial Research (NTNF).     

ON NEWMAN-TYPE RATIONAL INTERPOLATION TO ｜x｜ AT THE CHEBYSHEV NODES OF THE SECOND KIND

Recently Brutman and Passow considered Newman-type rational interpolation to ｜x｜ induced by arbitrary set of symmetric nodes in [-1,1] and gave the general estimation of the approximation error.By their methods one could establish the exact order of approximation for some special nodes. In the present paper we consider the special case where the interpolation nodes are the zeros of the Chebyshev polynomial of the second kind and prove that in this case the exact order of approximation is O（1/n｜nn）     

基于修正的第二类Chebyshev结点的Newman型有理插值函数对|x|的逼近

Recently Brutman and Passow considered Newman-type rational interpolation to ｜x｜ induced by arbitrary sets of symmetric nodes in [-1,1] and gave the general estimation of the approximation error.By their methods,one could establish the exact order of approximation for some special nodes.In the present note we consider the sets of interpolation nodes obtained by adjusting the Chebyshev roots of the second kind on the interval [0,1] and then extending this set to [-1,1] in a symmetric way.We show that in this case the exact order of approximation is O（ 1 n 2 ）.     

美式期权定价中非局部问题的有限元方法

在本文中 ,我们关心的是美式期权的有限元方法 .首先 ,根据 [4 ]我们对所讨论的问题引进一个新奇的实用的方法 ,它涉及到对原问题重新形成准确的数学公式 ,使得数值解的计算可以在非常小的区域上进行 ,从而该算法计算速度快精度高 .进而 ,我们利用超逼近分析技术得到了有限元解关于 L2 -模的最优估计 .     

累积两点信息的有理逼近RALND的改进

文献[1l提出了分子分母皆为线性函数的多元有理逼近(Rational Approximation with Linear Numerator and Denominator,RALND),满意地求了非线性方程组的解和数学规划最优解,为了克服RALND的不足,使之更好地发挥作用,本文试图改进该逼近:(1)提出了更合理地筛选有理逼近解的方法;(2)证明了该逼近的单调性;(3)对于原函数在当前点与前次迭代点连线方向上方向导数符号相反的情况,分别提出了迭代求有理逼近和构造在当前点与估算点连线方向上相应的方向导数符号相同的近似有理逼近的方法;(4)提出了一个非单调的有理逼近函数;(5)通过数值计算验证了本文提出的有理逼近是有效和可行的.     

Iterative approximation for a zero of accretive operator and fixed points problems in Banach space

In this paper we introduced an iteration scheme for viscosity approximation for a zero of accretive operator and fixed points problems in a reflexive Banach space with weakly continuous duality mapping. A new iterative sequence is introduced and strong convergence of the algorithm x_n is proved. The results improve and extend the results of Hu and Liu [L. Hu and L. Liu, A new iterative algorithm for common solutions of a finite family of accretive operators, Nonlinear Anal. 70 (2009) 2344-2351] and some others.     

ON SIGN FUNCTION AND SQUARE ROOT METHODS FOR SOLUTION OF REAL ALGEBRAIC RICCATI EQUATIONS

In this paper, we first justify the theory of the square root algorithm presented in [1], [2] by simple application of the matrix sign function, then we present an iterative square root algorithm for the continuous time algebraic Riccati equation.     

Curvature-Based Real-Time NURBS Surface Interpolator with Look-Ahead ACC/DEC Control

Real-time parametric surface interpolation is very useful in high-performance machining. A curvature-based NURBS surface interpolator with look-ahead acceleration/deceleration (ACC/DEC) control has been developed. The cutter contact (CC) paths are planned through iso-parametric line method. The CC feedrate profile is optimized using global flexible control strategy and local adaptive ACC/DEC optimization strategy according to the look-ahead algorithm. The real-time surface interpolation algorithm was programmed on Windows XP platform. The stability and efficiency of the proposed interpolation method were verified by a NURBS curve and a NURBS surface. It is shown that the proposed parametric interpolation algorithm can satisfy the high speed and high precision requirements of high-speed CNC systems.     

矩阵方程AXB+CYD=E的M对称解的迭代算法

在共轭梯度思想的启发下,结合线性投影算子,给出迭代算法求解了线性矩阵方程AXB+CYD=E的M对称解[X,Y]及其最佳逼近.当矩阵方程AXB+CYD=E有M对称解时,应用迭代算法,在有限的误差范围内,对任意初始M对称矩阵对[X_,Y_1],经过有限步迭代可得到矩阵方程的M对称解;选取合适的初始迭代矩阵,还可得到极小范数M对称解.而且,对任意给定的矩阵对[X,Y],矩阵方程AXB+CYD=E的最佳逼近可以通过迭代求解新的矩阵方程AXB+CYD=E的极小范数M对称解得到.文中的数值例子证实了该算法的有效性.