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1.
INTRODUCTION Offset curves/surfaces, also called parallel curves/surfaces, are defined as the locus of the points which are at constant distance along the normal from the generator curves/surfaces. As for a planar gen- erator curve Γ:C(t)=(x(t),y(t)), the parametric speed and its norm σ(t) are defined respectively as (Farouki, 1992) C ′( t ) =( x ′( t ), y ′(t )),σ (t ) = x ′ 2 (t ) y ′2(t ). (1) Subsequently the offset curve of the generator curve, which is at constant distanc… 相似文献
2.
The problem of parametric speed approximation of a rational curve is raised in this paper. Offset curves are widely used in
various applications. As for the reason that in most cases the offset curves do not preserve the same polynomial or rational
polynomial representations, it arouses difficulty in applications. Thus approximation methods have been introduced to solve
this problem. In this paper, it has been pointed out that the crux of offset curve approximation lies in the approximation
of parametric speed. Based on the Jacobi polynomial approximation theory with endpoints interpolation, an algebraic rational
approximation algorithm of offset curve, which preserves the direction of normal, is presented.
Project supported by the National Basic Research Program (973) of China (No. 2002CB312101) and the National Natural Science
Foundation of China (Nos. 60373033 and 60333010) 相似文献
3.
针对从散乱点云重建三角网格曲面的问题,提出了一个插值数据点的简单且鲁棒的曲面重建算法,其中点云是从任意拓扑的模型表面上采样得到的。利用最小二乘平面拟合方法计算每个点处的曲面法向,并计算两个等距面上相应的采样点,在构造好所有等距点的Delaunay三角剖分后,利用marching tetrahedra方法即可得到一个插值... 相似文献
4.
INTRODUCTIONTheOSSI(OffsetSurface/SurfaceIntersection)problemisasub-problemofgeneralSSI.AlthoughtheOSSIproblemcanberesolvedbyapplyinggeneralSSIalgorithm,itiscomputationallyexpensiveandexhaustive.Inrecentdecades,effortshavebeenfocusedoncomputingSSIexactly,efficiently,androbustlyinageneralsetting(Abdel-MalekandYeh,1997;Changetal.,1994;BurkeandSabharwal,1996;Mullenheim,1991).Thesetechniquescanbeclassifiedmainlyintofivecategories:algebraic,latticeevaluation,marching(tracing)method,… 相似文献
5.
Conventional methods for solving intersections between two offset parametric surfaces often include iteratively using computationally
expensive SSI (surface/surface intersections) algorithm. In addition, these methods ignore the relations between the intersection
curves of parametric surfaces with different offset distances. The algorithm presented in this paper, makes full use of the
topological relations between different intersection loops and calculates intersection loops with the help of previously calculated
intersection loops. It first pre-processes two parametric surfaces to obtain the characteristic points, called topology transition
points (TTPs), which can help in the subsequent finding of the topologies of the intersection curves. Then these points are
categorized into several distinct groups, and we can determine the calculation strategy for searching initial points by analyzing
the properties of these TTPs on the surfaces. Hence, all intersection curves can be marched from initial points by the tracing
algorithm. The proposed algorithm could calculate intersection curves robustly and effectively, and has been tested to be
capable of overcoming the degenerate conditions such as loop and singularities leaking that occur frequently in conventional
algorithms.
Project supported by the National Research Foundation for the Doctoral Program (No. 2000033554) of Higher Education of China
and the Natural Science Foundation of Zhejiang Province, China (No. 6001107) 相似文献
6.
INTRODUCTIONOffsetsareusedinmanyindustrialapplica-tions,suchastoolpathsinnumerical-control(NC)machining,planningpathsformobilerobotsandinCAD/CAMfields.TheparametricrepresentationofcurveinCAGDisbasedonemployingpolyno-mialorrationalfunction.Planecurveanditsoff-setsareusuallydefinedbyparametricformssuchasr(t)=(x(t),y(t));offsetsared()()()ttdt=眗rn,n(t)isnormalvectorofr(t),disdistancealongn(t).Butthegenerationofoffsetcurvesisnotasimpletaskbecausen(t)ingeneralhasnorationalexpression.Sofar… 相似文献
7.
In this paper,a G1, C1, C2 PH-spline is employed as an approximation for a given Bézier curve within error bound and further renders offset which can be regarded as an approximate offset to the Bézier curve. The errors between PH-spline and the Bézier curve, the offset to PH-spline and the offset to the given Bézier curve are also estimated. A new algorithm for constructing offset to the Bézier curve is proposed. 相似文献
8.
In this paper, a G1, C1, C2 PH-spline is employed as an approximation for a give Bézier curve within error bound and further renders offset which can
be regarded as an approximate offset to the Bézier curve. The errors between PH-spline and the Bézier curve, the offset to
PH-spline and the offset to the given Bézier curve are also estimated. A new algorithm for constructing offset to the Bézier
curve is proposed.
Project supported by the National Natural Foundation of China (No. 60073023) and the National Basic Research Program (973)
of China (No. 2002CB312101) 相似文献
9.
In this paper, we consider the set partitioning problem with matroid constraint, which is a generation of the k-partitioning problem. The objective is to minimize the weight of the heaviest subset. We present an approximation algorithm, which consists of two sub-algorithms--the modified Edmonds＇ matroid partitioning algorithm and the exchange algorithm, for the problem. An estimation of the worst ratio for the algorithm is given. 相似文献
10.
11.
赵忠伟 《浙江大学学报(A卷英文版)》2006,7(3):321-325
INTRODUCTION Orthogonal frequency division multiplexing (OFDM) has been treated as the key transmission method in Wireless Local Area Networks (WLANs) based on IEEE802.11a protocol (IEEE Standard 802.11a- 1999). However, the sensitivity of the scheme to the frequency offset limits its development. Moose (1994) proposed maximum likelihood esti-mation for the carrier frequency offset by using two different received symbols, but the limitation of this method is that the acquisition r… 相似文献
12.
This paper presents the forward displacement analysis of an 8-PSS （prismatic-spherical-spherical） redundant parallel manipulator whose moving platform is linked to the base platform by eight kinemtic chains consisting of a PSS joint and a strut with fixed length. A general approximation algorithm is used to solve the problem. To avoid the extraction of root in the approximation process, the forward displacement analysis of the 8-PSS redundant parallel manipulator is transformed into another equivalent problem on the assumption that the strut is extensible while the slider is fixed. The problem is solved by a modified approximation algorithm which predicates that the manipulator will move along a pose vector to reduce the difference between the desired configuration and an instantaneous one, and the best movement should be with minimum norm and least quadratic sum. The characteristic of this modified algorithm is that its convergence domain is larger than that of the general approximation algorithm. Simulation results show that the modelified algorithm is general and can be used for the forward displacement analysis of the redundant parallel manipulator actuated by a revolute joint. 相似文献
13.
杨克领 《商丘职业技术学院学报》2007,6(5):43-45
随机化算法的流程和结果受所使用的随机函数的影响，按影响的性质和程度分为“随机不影响算法的执行结果”、“随机影响执行结果的正确性”、“随机影响执行结果的优劣”三种情况，主要表现在算法的时间效率上．用随机函数全部或部分地抵消最坏输入，可使算法的时间效率不完全依赖于输入的好坏，通过对输入的适当控制，使得执行结果相对稳定． 相似文献
14.
本文主要研究基因无方向的基因组重排的反转排序问题.本文算法基于断点图的概念,给出一个时间复杂性为O(maxb3(π),nb(π)),空间复杂性为O(n)的求解近似最优解的算法,其中n为基因组中基因个数,π=(π1,π2,...πn)表示n个基因的一种排列,b(π)表示排列π中的断点数.数据试验的结果表明,该近似算法可以求得较好的结果. 相似文献
15.
唐金花 《金华职业技术学院学报》2008,8(6):1-3
本文在分析MIMO-QAM系统可行性的基础上,提出了一种频偏估计算法,并进行了仿真。该算法利用帧同步序列,优化系统资源配置。仿真结果表明,本文提出的算法是可行的,具有较高的精度和实用价值。 相似文献
16.
WANG Yong-cai ZHAO Qian-chuan ZHENG Da-zhong 《浙江大学学报(A卷英文版)》2006,7(6):927-936
INTRODUCTION With the prevalence of distributed computing and parallel programming languages (Barry and Allen, 1998), performance evaluation of the parallel execu-tion systems becomes important. In this work we derive bounds and an approximation of the mean response time of a particular type parallel program: program with Fork-Join tasks and executed in multi-processor with first come first served (FCFS) policy. This kind of program is general in large-scale simu-lation and numerical … 相似文献
17.
郑志国 《华南师范大学学报(社会科学版)》2012,3(3):91-98,163
古典经济学家和马克思对等量资本获得等量利润的认识基本上限于对假设数据的分析,其结论并没有得到调查统计资料的证实.国内外有关调查统计资料表明,各部门的实际利润率并不平均.实际利润率受多种作用方向不同的因素影响,有些因素引起利润率平均化,还有些因素引起利润率非平均化.这两种因素的作用部分抵消,其中引起利润率非平均化的因素作用更强,包括企业追求利润最大化的动因和行为、不同部门劳动质量和生产成本差异、生产资本专业化和转移障碍、信息不完全、需求变化对供给变化的抵消作用.这些因素的作用使投入不同部门的等量资本难以获得等量利润. 相似文献
18.
Jia Liu Xiangbin Meng Gongjun Xu Wei Gao Ningzhong Shi 《Journal of Educational Measurement》2024,61(1):99-124
In this paper, we develop a mixed stochastic approximation expectation-maximization (MSAEM) algorithm coupled with a Gibbs sampler to compute the marginalized maximum a posteriori estimate (MMAPE) of a confirmatory multidimensional four-parameter normal ogive (M4PNO) model. The proposed MSAEM algorithm not only has the computational advantages of the stochastic approximation expectation-maximization (SAEM) algorithm for multidimensional data, but it also alleviates the potential instability caused by label-switching, and then improved the estimation accuracy. Simulation studies are conducted to illustrate the good performance of the proposed MSAEM method, where MSAEM consistently performs better than SAEM and some other existing methods in multidimensional item response theory. Moreover, the proposed method is applied to a real data set from the 2018 Programme for International Student Assessment (PISA) to demonstrate the usefulness of the 4PNO model as well as MSAEM in practice. 相似文献
19.
As one of the most important components of the wideband wireless access technique, orthogonal frequency division multiplexing （OFDM） has a high usage rate of spectrum and combats inter-symbol interference （ISI） in multi-path fading channel. However, when there are frequency offsets during the signal transmission, the inter-carrier interference （ICI） is introduced, which significantly degrades the performance. The existing ICI self-cancellation schemes such as PCC-OFDM are not optimum to minimize the interference considering both noise and ICI. In this paper, a new metric named S1NR （signal-to-interference- and-noise ratio） is proposed. We discuss the optimization issue when a constant frequency offset exists and in time-varying channels. The optimum weighting-coefficient-pair （OWCP） is obtained, which maximizes SINR theoretically through the alternant iteration algorithm. Simulations show that the performance of OWCP-OFDM is better than that of PCC-OFDM, especially when the frequency offset is large. Although the ICI self-cancellation scheme suffers bandwidth inefficiency, from the simulation results we can also see that the performance of OWCP-OFDM is much better than that of the standard OFDM systems with the same bandwidth efficiency when a frequency offset exists. Moreover, since the redundant modulation provides the capability to suppress ICI as well as a receiving SNR gain, it can be considered as exchanging the bandwidth for SNR. 相似文献
20.
The transfer matrix of wrist force sensor is important for decoupling theoutput signals and enhancing the precision of wrist force sensor.This paper solves thetransfer matrix from the realization of optimal approximation of polynomial.First,thegeneral transfer matrix algorithm in the sense of L~2 and two kinds of modified algorithmare proposed.Then,starting from uniform approximation,the optimal transfer matrixalgorithm is offered and solved by the use of linear programming.The results of experi-ment and computation prove that these algorithms are effective. 相似文献