《代数与几何基础》(张肇炽教授主编)一书评析

数学是研究现实事物的数量关系与空间形式的一门科学 .分析学、代数学与几何学是数学的三大基础 ,分析与代数侧重于数学中的“数”,而几何则侧重于数学中的“形”.坐标、向量、矩阵等概念的建立 ,将代数和几何紧密地结合在一起 ,代数为几何提供了研究方法 ,而几何也为代数提供了直观的几何背景 .事实上 ,线性代数中所讨论的“线性”概念来源欧氏几何、线性方程组理论和解析几何 ,线性空间的概念是几何空间的一种代数抽象 .变换的理论 ,如正交变换、仿射变换、射影变换等都是从几何中产生的 .线性代数中的很多重要概念 ,如矩阵的等价、相合、…     

Clifford 代数,几何计算和几何推理

Clifford代数是一种深深根植于几何学之中的代数系统,被它的创始人称为几何代数．历史上,E．Cartan,R．Brauer,H．Weyl,C．Chevalley等数学大师都曾研究和应用过Clifford代数,对它的发展起了重要作用．近年来,Clifford代数在微分几何、理论物理、经典分析等方面取得了辉煌的成就,是现代理论数学和物理的一个核心工具,并在现代科技的各个领域,如机器人学、信号处理、计算机视觉、计算生物学、量子计算等方面有广泛的应用．本文主要介绍Clifford代数在几何计算和几何推理中的应用．作为一种优秀的描述和计算几何问题的代数语言,Clifford代数对于几何体,几何关系和几何变换有不依赖于坐标的、易于计算的多种表示,因而应用它进行几何自动推理,不仅使困难定理的证明往往变得极为简单,而且能够解决一些著名的公开问题,目前在国际上,几何自动推理已经成为Clifford代数的一个重要应用领域。     

以结构思想为切入点把握向量的教学

向量是研究几何的一种基本工具 ,这种工具把几何结构转化为代数结构 ,实现几何代数化 .因此 ,在向量教学中 ,要让学生知道向量工具如何把几何结构转化为代数结构 ,利用结构思想分析问题、解决问题成为我们教学的关键问题 .为此 ,对这两方面作如下探讨 .1　几何结构转为代数结构 ,实现几何代数化几何历史的发展 ,大概经历了实验几何、综合推理几何、三角学和解析几何等四个阶段 .要使几何学实现根本转变 ,出路在于代数化 .综合几何发展到解析几何的过程 ,找到了几何问题解决通法 ,真正实现几何代数化 .用代数方法去研究几何问题是数学史上一…     

向量与几何

向量是现代数学的基本概念之一，也是解几何题的有力工具．向量法就是把几何问题代数化．然后用代数的运算来解几何题．用向量工具处理几何题，兼有几何的直观性、运算表述的简洁性和代数方法的一般性．本讲主要探讨这一方法．     

共形几何代数中的分阶幂零单项式的几何解释

本文进一步发展共形几何代数,从代数和几何两个角度对共形几何代数中由幂零向量生成的分阶单项式的代数性质和几何解释进行深入探讨,包括各种维数的球面和平面定向的代数刻画、长括号的三角学、角度和方向的幂零单项式分阶表示、幂零单项式各个分阶的几何意义等.这些结果有助于理解高层次符号代数运算背后的几何意义,以及共形几何代数简化符号几何计算的内在机制.     

二十一世纪的数学

今天我很荣幸能有这个机会同大家讲话。我先讲两个故事。 我们都知道欧几里得(Eiclid)的《几何原本》,这是一本数学方面的论著,完成于2000多年以前。它对于人类是一个很伟大的贡献。书中包括了分析和代数,不限于几何,目的是     

关注几何性质 简化解题过程

众所周知,解析几何就是用代数的方法来研究和解决几何问题的一门数学分支,它的产生,使我们研究几何问题有了可以入微的代数手段;其思想方法,对于数学或者现代科学来说,都具有划时代的意义．不过,当我们用代数方法进行相应研究的同时,     

对话李克正教授：为什么学习代数几何

以与首都师范大学的李克正教授对话的方式,通过其口简要介绍代数几何这门重要学科在我国的早期发展情况,详细回忆李克正教授在国外学习代数几何的过程,以及他回国后的教学与研究成果,并通俗地阐述代数几何方法对于解决重大数论问题所起的关键作用．     

几何直观在线性代数教学中的应用

本强调了几何直观在线性代数教学中的作用，通过例子从代数概念的引入、代数性质的几何解释、代数理论应用的直观分析几个方面加以说明。     

实对称型上的Schur子空间及应用

本文构作了Schur型多项式,将其作为研究实对称型的基础.研究了具有零点(1,1,...,1)的实对称型形成的子空间,即Schur子空间.建立了这种子空间的构造性理论,并应用于计算(构造)实代数几何中比较关心的对称型正性判定问题,以及给出一些特殊类型的Hilbert第17问题的构造解.     

Semidefinite programming relaxations for semialgebraic problems

 A hierarchy of convex relaxations for semialgebraic problems is introduced. For questions reducible to a finite number of polynomial equalities and inequalities, it is shown how to construct a complete family of polynomially sized semidefinite programming conditions that prove infeasibility. The main tools employed are a semidefinite programming formulation of the sum of squares decomposition for multivariate polynomials, and some results from real algebraic geometry. The techniques provide a constructive approach for finding bounded degree solutions to the Positivstellensatz, and are illustrated with examples from diverse application fields. Received: May 10, 2001 / Accepted May 2002 Published online: April 10, 2003 Key Words. semidefinite programming – convex optimization – sums of squares – polynomial equations – real algebraic geometry The majority of this research has been carried out while the author was with the Control & Dynamical Systems Department, California Institute of Technology, Pasadena, CA 91125, USA.     

(2, 1)-Separating systems beyond the probabilistic bound

Building on previous results of Xing, we give new lower bounds on the rate of linear intersecting codes over large alphabets. The proof is constructive, and uses algebraic geometry (although nothing beyond the basic theory of linear systems on curves). Then, using these new bounds within a concatenation argument, we construct binary (2,1)-separating systems of asymptotic rate exceeding the one given by the probabilistic method, which was the best lower bound available up to now. This answers (negatively) the question of whether this probabilistic bound was exact, which has remained open for more than 30 years.     

On cyclic algebraic-geometry codes

In this paper we initiate the study of cyclic algebraic geometry codes. We give conditions to construct cyclic algebraic geometry codes in the context of algebraic function fields over a finite field by using their group of automorphisms. We prove that cyclic algebraic geometry codes constructed in this way are closely related to cyclic extensions. We also give a detailed study of the monomial equivalence of cyclic algebraic geometry codes constructed with our method in the case of a rational function field.     

微分多项式系统的约化算法理论

本文中，作者推广了纯代数形式的特征列集理论（吴方法）为微分形式的相应理论，即建立了在机器证明了诸多微分问题中非常重要的微分多项式组的约化算法理论。引入了一些新的概念和观点使函数微分（导数）具有直观的代数几何表示。给出了Coherent条件下的特征列集的算法。给出的算法易于在计算机上实现并适合应用于广泛的微分问题，如微分方程对称计算，各种微分关系的自动推理等问题。     

Algebra-geometry of piecewise algebraic varieties

Algebraic variety is the most important subject in classical algebraic geometry. As the zero set of multivariate splines, the piecewise algebraic variety is a kind generalization of the classical algebraic variety. This paper studies the correspondence between spline ideals and piecewise algebraic varieties based on the knowledge of algebraic geometry and multivariate splines.     

The correspondence between multivariate spline ideals and piecewise algebraic varieties

As a piecewise polynomial with a certain smoothness, the spline plays an important role in computational geometry. The algebraic variety is the most important subject in classical algebraic geometry. As the zero set of multivariate splines, the piecewise algebraic variety is a generalization of the algebraic variety. In this paper, the correspondence between piecewise algebraic varieties and spline ideals is discussed. Furthermore, Hilbert’s Nullstellensatz for the piecewise algebraic variety is also studied.     

Nöther-type theorem of piecewise algebraic curves on quasi-cross-cut partition

Nöther’s theorem of algebraic curves plays an important role in classical algebraic geometry. As the zero set of a bivariate spline, the piecewise algebraic curve is a generalization of the classical algebraic curve. Nöther-type theorem of piecewise algebraic curves is very important to construct the Lagrange interpolation sets for bivariate spline spaces. In this paper, using the characteristics of quasi-cross-cut partition, properties of bivariate splines and results in algebraic geometry, the Nöther-type theorem of piecewise algebraic curves on the quasi-cross-cut is presented.     

The correspondence between multivariate spline ideals and piecewise algebraic varieties

As a piecewise polynomial with a certain smoothness, the spline plays an important role in computational geometry. The algebraic variety is the most important subject in classical algebraic geometry. As the zero set of multivariate splines, the piecewise algebraic variety is a generalization of the algebraic variety. In this paper, the correspondence between piecewise algebraic varieties and spline ideals is discussed. Furthermore, Hilbert’s Nullstellensatz for the piecewise algebraic variety is also studied.     

Implicit algebraic geometry on categories of universal algebras

Using the notion of an implicit operation on universal algebras, we redefine basic notions of the algebraic geometry of universal algebras. The results obtained for the implicit algebraic geometry imply (as special cases) the known results on the conditional geometric and algebraic geometric comparability of algebras.