共查询到20条相似文献,搜索用时 95 毫秒
1.
程少华 《数学的实践与认识》2007,37(1):61-65
曲面重构是逆向工程中的关键技术.根据非均匀有理B样条曲面矩阵表达式,对于造型曲面上的(2m+1)×(2n+1)个型值数据点,推导了一个仅利用型值点数据反算二次非均匀有理B样条曲面控制顶点的算法.数值算例表明了该算法的有效性. 相似文献
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双三次B样条插值曲面 总被引:2,自引:0,他引:2
本文研究三次B样条插值曲面。对于给定的拓扑网格点阵Pi,j。导出了其插值三次B样条曲面的控制顶点,每四个顶点Pi,j,Pi l,j,Pi,j 1,Pi 1,j 1由九个三次B样条曲面片构成,整个曲面是C^2连续的,最后,给出了一个数值实例。 相似文献
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NURBS曲线曲面拟合数据点的迭代算法 总被引:1,自引:0,他引:1
本文推广了文献[1]的结果,将文献[1]中关于B样条曲线曲面拟合数据点的迭代算法推广至有理形式,给出了无需求解方程组反求控制点及权因子即可得到拟合NURBS曲线曲面的迭代方法.该算法和文献[1]的算法本质上是统一的,而后者恰是前者的一种退化形式.文章还给出了收敛性证明以及一些定性分析.文末的数值实例说明该算法简单实用. 相似文献
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T-B样条曲线及其应用 总被引:9,自引:0,他引:9
给出一种基于三角函数的类B样条设计方法,称其为 T B样条,它具有 B样条曲线曲面的主要优点,它还能够无需有理形式即可精确表示圆弧、椭圆弧等二次曲线弧以及球面、椭球面等二次曲面片. 相似文献
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$A_{1}$型扩张仿射Lie代数的分类依赖于从Euclid空间中的半格构造得到的TKK代数. Allison等从${\mathbb {R}}^{\nu}(\nu\geq1)$的一个半格出发, 定义了一类Jordan代数. 然后通过所谓的Tits-Kantor-Koecher方法构造出TKK代数${\cal{T}}({\cal J}(S))$, 最后得到$A_{1}$型扩张仿射Lie代数. 在${\mathbb{R}}^{2}$中, 只有两个不相似的半格$S$和$S’$, 其中$S$是格而$S’$是非格半格. 本文主要研究TKK代数${\cal{T}}({\cal J}(S))$的${\mathbb {Z}}^{2}$-分次自同构. 相似文献
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本文首先针对散乱数据拟合的Shepard方法,结合截断多项式、B样条基函数和指数函数来构造其权函数,使新的权函数具有更高的光滑度和更好的衰减性,并且其光滑性和衰减性可以根据实际需要自由调节,从而提高了曲面的拟合质量.同时还给出一种类似的局部插值方法.另外,本文还基于多重二次插值,结合多元样条的思想,给出了两个局部插值算法.该算法较好地继承了多重二次插值曲面的性质,从而保证了拟合曲面具有好地光顺性和拟合精度.曲面整体也具有较高的光滑性. 相似文献
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研究了由三维Minkowski空间$E^3_1$中一个类空曲面$S_1$上一个单参数测地曲线族的切线所构成的直线汇$T$,它以$S_1$为一个焦曲面.证明了$T$的两个可展曲面族沿着第二个焦曲面$S_2$的正交曲线网相交的充要条件是$S_1$是可展曲面.对于$T$的两个焦曲面$S_1$和$S_2$之间沿着同一光线的对应,还证明了其保持渐近曲线网的充要条件.最后,研究了$T$的正交曲面$S$,并且证明了如果$S$是$E^3_1$中的一个极大曲面,那么,$T$的焦曲面$S_1$和$S_2$之间沿着同一光线的对 相似文献
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一类双k次B样条曲面的G1连续性条件 总被引:2,自引:0,他引:2
本文针对两个k×k次B样条曲面的节点向量为端点插值、内部是单节点的情形 ,给出它们之间的G1光滑拼接条件 ,同时得到它们的公共边界曲线的控制顶点所要满足的本征方程 .其中本征方程是B样条曲面片所独有的现象 . 相似文献
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Suppose $\cal{S}^1({\cal T})\subset H^1(\Omega)$ is the $P_1$-finite element
space of $\cal{T}$-piecewise affine functions
based on a regular triangulation $\cal{T}$ of a two-dimensional surface
$\Omega$ into triangles.
The $L^2$ projection $\Pi$ onto $\cal{S}^1(\cal{T})$ is $H^1$ stable
if $\norm{\Pi v}{H^1(\Omega)}\le C\norm{v}{H^1(\Omega)}$ for
all $v$ in the Sobolev space $H^1(\Omega)$ and if the bound $C$
does not depend on the mesh-size in $\cal{T}$ or on the
dimension of $\cal{S}^1(\cal{T})$.
\hskip 1em A red–green–blue refining adaptive algorithm is designed which
refines a coarse mesh $\cal{T}_0$ successively such that each triangle is
divided into one, two, three, or four subtriangles.
This is the newest vertex bisection supplemented with possible red refinements
based on a careful initialization.
The resulting finite element space allows
for an $H^1$ stable $L^2$ projection.
The stability
bound $C$ depends only on the coarse mesh $\cal{T}_0$ through the number of
unknowns, the shapes of the triangles in $\cal{T}_0$, and possible
Dirichlet boundary conditions. Our arguments also
provide a discrete version
$\norm{h_\cal{T}^{-1}\,\Pi v}{L^2(\Omega)}\le C\norm{h_\cal{T}^{-1}\,v}{L^2(\Omega)}$
in $L^2$ norms weighted with the mesh-size $h_\T$. 相似文献
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本文利用差方法对自反MD设计SCMD$(4mp, p,1)$的存在性给出了构造性证明, 这里$p$为奇素数, $m$为正整数. 相似文献
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The truncated hierarchical B-spline basis has been proposed for adaptive data fitting and has already drawn a lot of attention in theory and applications.However the stability with respect to the L_p-norm,1≤p∞,is not clear.In this paper,we consider the L_p stability of the truncated hierarchical B-spline basis,since the L_p stability is useful for curve and surface fitting,especially for least squares fitting.We prove that this basis is weakly L_p stable.This means that the associated constants to be considered in the stability analysis are at most of polynomial growth in the number of the hierarchy depth. 相似文献
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\small\zihao{-5}\begin{quote}{\heiti 摘要:} 设$M$为$n+1$维单位球面$S^{n+1}(1)$中的一个极小闭超曲面,如果 $ n \le S \le n+\frac{2}{3}$, 则有 $S=n$ 且 $M$ 与某一Clifford 环面 $S^m(\sqrt{m/n}) \times S^{n-m}(\sqrt{(n-m)/n})$等距. 相似文献
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Let $P$ be a set of $n$ points in $\Re^d$. The {\em
radius} of a $k$-dimensional flat ${\cal F}$ with
respect to $P$, which we denote by ${\cal RD}({\cal F},P)$,
is defined to be $\max_{p \in P} \mathop{\rm dist}({\cal F},p)$, where
$\mathop{\rm dist}({\cal F},p)$ denotes the Euclidean distance between
$p$ and its projection onto ${\cal F}$. The $k$-flat
radius of $P$, which we denote by ${R^{\rm opt}_k}(P)$, is the
minimum, over all $k$-dimensional flats ${\cal F}$, of
${\cal RD}({\cal F},P)$. We consider the problem of
computing ${R^{\rm opt}_k}(P)$ for a given set of points $P$. We
are interested in the high-dimensional case where $d$ is
a part of the input and not a constant. This problem is
NP-hard even for $k = 1$. We present an algorithm that,
given $P$ and a parameter $0 < \eps \leq 1$, returns a
$k$-flat ${\cal F}$ such that ${\cal RD}({\cal F},P) \leq (1 +
\eps) {R^{\rm opt}_k}(P)$. The algorithm runs in $O(nd
C_{\eps,k})$ time, where $C_{\eps,k}$ is a constant that
depends only on $\eps$ and $k$. Thus the algorithm runs
in time linear in the size of the point set and is a
substantial improvement over previous known algorithms,
whose running time is of the order of $d
n^{O(k/\eps^c)}$, where $c$ is an appropriate constant. 相似文献
17.
Kite-可分组设计的相交数问题是确定所有可能的元素对$(T,s)$, 使得存在一对具有相同组型 $T$ 的Kite-可分组设计 $(X,{\cal H},{\cal B}_1)$ 和$(X,{\cal H},{\cal B}_2)$ 满足$|{\cal B}_1\cap {\cal B}_2|=s$. 本文研究组型为 $2^u$ 的Kite-可分组设计的相交数问题, 设 $J(u)=\{s:\exists$ 组型为 $2^u$ 的Kite-可分组设计相交于$s$ 个区组\}, $I(u)=\{0,1,\ldots,b_{u}-2,b_{u}\}$,其中 $b_u=u(u-1)/2$ 是组型为$2^u$ 的Kite-可分组设计的区组个数. 我们将给出对任意整数 $u\ge 4$ 都有$J(u)=I(u)$ 且 $J(3)= \{0,3\}$. 相似文献
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1引言 B样条在计算机图形学和几何建模等领域有着广泛的应用[3,8].在应用过程中,通常都需要对得到的模型进行修改以到达更好的效果.对于B样条曲线,利用节点插入算法可以有效地进行局部修改. 相似文献
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Mehrotra-type predictor-corrector algorithm,as one of most efficient interior point methods,has become the backbones of most optimization packages.Salahi et al.proposed a cut strategy based algorithm for linear optimization that enjoyed polynomial complexity and maintained its efficiency in practice.We extend their algorithm to P*(κ)linear complementarity problems.The way of choosing corrector direction for our algorithm is different from theirs. The new algorithm has been proved to have an ο((1+4κ)(17+19κ) √(1+2κn)3/2log[(x0)Ts0/ε] worst case iteration complexity bound.An numerical experiment verifies the feasibility of the new algorithm. 相似文献