Implicitization of Parametric Curves via Lagrange Interpolation

A simple algorithm for finding the implicit equation of a parametric plane curve given by its parametric equations is presented. The algorithm is based on an efficient computation of the Bézout resultant and Lagrange interpolation. One of main features of our approach is the fact that it considerably reduces the problem of computing intermediate expressions.     

On the structure of 2-D observers

This note gives necessary and sufficient conditions for asymptotic reconstructibility of the state of multivariable 2D systems. The existence and the structure of the observers are related to the matrices appearing in a Bézout identity. A counterexample shows that the state estimation cannot be performed in general by a static feedback on the estimation error. This note includes also a technique for designing dynamic state observers.     

A formal theory of matrix primeness

Primeness of nD polynomial matrices is of fundamental importance in multidimensional systems theory. In this paper we define a quantity which describes the “amount of primeness” of a matrix and identify it as the concept of grade in commutative algebra. This enables us to produce a theory which unifies many existing results, such as the Bézout identities and complementation laws, while placing them on a firm algebraic footing. We also present applications to autonomous systems, behavioural minimality of regular systems, and transfer matrix factorization. This work has been sponsored by EPSRC Grant No. GR/K 18504.     

Behavioral controllability and coprimeness for pseudorational transfer functions

Controllability plays various crucial roles in behavioral system theory. While there exist several characterizations of this notion, in terms of the Bézout identity, image representation, direct sum decomposition, etc., its overall picture for infinite-dimensional systems still remains rather incomplete, in spite of various existing attempts. This article gives an extension of such results in a well-behaved class of infinite-dimensional systems, called pseudorational. A proper choice of an algebra makes the treatment more transparent. We establish equivalent conditions for controllability in terms of the Bézout identity, relationships with notions such as image representation and direct sum decompositions.     

一类有理曲线—RB曲线

为了进一步丰富 Bézier曲线理论 ,首先从 Bernstein基函数出发 ,构造了一类新型函数—— Bernstein函数类 ,同时讨论了它的性质 ;然后用该类函数给出了 Bézier曲线类的生成方法 ;重点研究了一类基于有理形式调配函数的实用曲线—— RB曲线 ,结果表明 ,附加权因子的 RB曲线能部分克服常用的有理 Bézier曲线的权因子的选取没有统一的规则可以遵循的局限 ,提高了曲线设计的灵活性 ;最后给出了实例 ,并得到了可视化结果 .     

Bilinear precision of rational Bézier surfaces

This short note proves the bilinear precision property of rational Bézier surfaces and gives a simple algorithm to compute the weights. Linear precision of rational Bézier surfaces is also discussed.     

Design of controllers by indices of precision and speed. II. Nonminimal-phase plants

A method to design controllers of one-dimensional nonminimal-phase plants under unknown bounded external perturbations was proposed. It is based on determining the parameters of the Bézout identity. The attainable indices of precision and speed were determined.     

Eliciting dependability requirements: a control cases based approach

At present,great demands are posed on software dependability.But how to elicit the dependability requirements is still a challenging task.This paper proposes a novel approach to address this issue.The essential idea is to model a dependable software system as a feedforward-feedback control system,and presents the use cases+control cases model to express the requirements of the dependable software systems.In this model,while the use cases are adopted to model the functional requirements,two kinds of control cases(namely the feedforward control cases and the feedback control cases)are designed to model the dependability requirements.The use cases+control cases model provides a unified framework to integrate the modeling of the functional requirements and the dependability requirements at a high abstract level.To guide the elicitation of the dependability requirements,a HAZOP based process is also designed.A case study is conducted to illustrate the feasibility of the proposed approach.     

Wavelet Rasterization

We present a method for analytically calculating an anti‐aliased rasterization of arbitrary polygons or fonts bounded by Bézier curves in 2D as well as oriented triangle meshes in 3D. Our algorithm rasterizes multiple resolutions simultaneously using a hierarchical wavelet representation and is robust to degenerate inputs. We show that using the simplest wavelet, the Haar basis, is equivalent to performing a box‐filter to the rasterized image. Because we evaluate wavelet coefficients through line integrals in 2D, we are able to derive analytic solutions for polygons that have Bézier curve boundaries of any order, and we provide solutions for quadratic and cubic curves. In 3D, we compute the wavelet coefficients through analytic surface integrals over triangle meshes and show how to do so in a computationally efficient manner.     

Surface parameterization of nonsimply connected planar Bézier regions

A technique is described for constructing three-dimensional vector graphics representations of planar regions bounded by cubic Bézier curves, such as smooth glyphs. It relies on a novel algorithm for compactly partitioning planar Bézier regions into nondegenerate Coons patches. New optimizations are also described for Bézier inside–outside tests and the computation of global bounds of directionally monotonic functions over a Bézier surface (such as its axis-aligned bounding box or optimal field-of-view angle). These algorithms underlie the three-dimensional illustration and typography features of the TeX-aware vector graphics language Asymptote.     

A Subdivision Scheme for Rational Triangular Bézier Surfaces

An explicit formula is developed to decompose a rational triangular Bezier patch into three non-degenerate rational rectangular Bezier patches of the same degree.This formula yields a stable algorithm to compute the control vertices of those three rectangular subpatches.Some properties of the subdivision are discussed and the formula is illustrated with an example.     

Low-harmonic rational Bézier curves for trajectory generation of high-speed machinery

For a given high-speed machinery, a significant source of the internally induced vibrational excitation is the presence of high frequency harmonics in the trajectories that the system is forced to follow. In this paper a special class of rational Bézier curves is presented that correspond to low-harmonic trajectory patterns. Harmonic Bernstein polynomials and harmonic deCasteljau algorithm are also introduced as two major tools for generating the harmonic rational Bézier curves. These curves can be used to synthesize trajectories within the dynamic response limitations of the actuators while avoiding the excitation of the natural modes of vibration of the system.     

Recursive formulation of the matrix Padé approximation in packed storage

The Extended Euclidean algorithm for matrix Padé approximants is applied to compute matrix Padé approximants when the coefficient matrices of the input matrix polynomial are triangular. The procedure given by Bjarne S. Anderson et al. for packing a triangular matrix in recursive packed storage is applied to pack a sequence of lower triangular matrices of a matrix polynomial in recursive packed storage. This recursive packed storage for a matrix polynomial is applied to compute matrix Padé approximants of the matrix polynomial using the Matrix Padé Extended Euclidean algorithm in packed form. The CPU time and memory comparison, in computing the matrix Padé approximants of a matrix polynomial, between the packed case and the non-packed case are described in detail.     

Approximate polynomial GCD over integers

Symbolic numeric algorithms for polynomials are very important, especially for practical computations since we have to operate with empirical polynomials having numerical errors on their coefficients. Recently, for those polynomials, a number of algorithms have been introduced, such as approximate univariate GCD and approximate multivariate factorization for example. However, for polynomials over integers having coefficients rounded from empirical data, changing their coefficients over reals does not remain them in the polynomial ring over integers; hence we need several approximate operations over integers. In this paper, we discuss computing a polynomial GCD of univariate or multivariate polynomials over integers approximately. Here, “approximately” means that we compute a polynomial GCD over integers by changing their coefficients slightly over integers so that the input polynomials still remain over integers.     

Construction of Bézier points of quadrilaterals from those of triangles

A simple algorithm is given which calculates the Bézier points of a surface over a quadrangle from the given generalized Bézier points of the surface over a triangle. An example is added.     

A generalized unconstrained theory and isogeometric finite element analysis based on Bézier extraction for laminated composite plates

This work presents an isogeometric finite element formulation based on Bézier extraction of the non-uniform rational B-splines (NURBS) in combination with a generalized unconstrained higher-order shear deformation theory (UHSDT) for laminated composite plates. The proposed approach relaxes zero-shear stresses at the top and bottom surfaces of the plates and no shear correction factors are required. A weak form of static, free vibration and transient response analyses for laminated composite plates is then established and is numerically solved using isogeometric Bézier finite elements. NURBS can be written in terms of Bernstein polynomials and the Bézier extraction operator. IGA is implemented with the presence of C°-continuous Bézier elements which allow to easily incorporate into existing finite element codes without adding many changes as the former IGA. As a result, all computations can be performed based on the basis functions defined previously as the same way in finite element method (FEM). Numerical results performed over static, vibration and transient analysis show high efficiency of the present method.     

Poisson曲线的递推求值

计算Bézier曲线上一点的DeCasteljau递推算法和计算B样条曲线上一点的DeBoor递推算法是计算机辅助几何设计(CAGD)领域里的两个经典算法。它们使得计算曲线上一点变得直观和快捷,非常适合用计算机编程实现。文章对Poisson曲线进行了研究,在上述算法的基础上,提出了计算Poisson曲线上一点的递推算法,并将其推广到有理Poisson曲线的情形,提出了有理Poisson曲线的递推算法。     

Weakly coprime factorization and state-feedback stabilization of discrete-time systems

The LQ-optimal state feedback of a finite-dimensional linear time-invariant system determines a coprime factorization NM ⁻¹ of the transfer function. We show that the same is true also for infinite-dimensional systems over arbitrary Hilbert spaces, in the sense that the factorization is weakly coprime, i.e., Nf, for every function f. The factorization need not be Bézout coprime. We prove that every proper quotient of two bounded holomorphic operator-valued functions can be presented as the quotient of two bounded holomorphic weakly coprime functions. This result was already known for matrix-valued functions with the classical definition gcd(N, M) = I, which we prove equivalent to our definition. We give necessary and sufficient conditions and further results for weak coprimeness and for Bézout coprimeness. We then establish a variant of the inner–outer factorization with the inner factor being “weakly left-invertible”. Most of our results hold also for continuous-time systems and many are new also in the scalar-valued case.     

基于微粒群算法的有理Bézier曲线降阶

从最优化思想出发，把有理Bézier曲线的降阶问题转化为求解优化问题，并基于微粒群算法，给出有理Bézier曲线降阶的一种新方法。该方法可以实现多次降阶，且降阶后的有理Bézier曲线直接以显式给出。最后结合实例，与使用遗传算法进行有理Bézier曲线降阶的结果进行对比，实验结果表明了微粒群算法的有效性。