Fermat point for a triangle in three dimensions using the taxicab metric

This article explores the process of finding the Fermat point for a triangle ABC in three dimensions. Three examples are presented in detail using geometrical methods. A delightfully simple general method is then presented that requires only the comparison of coordinates of the vertices A, B and C.     

The taxicab locus of Apollonius: promoting exploratory routes to the punchline using rich undergraduate tasks

ABSTRACT

A key motivational tactic in undergraduate mathematics teaching is to launch topics with fundamental questions that originate from surprising or remarkable phenomena. Nonetheless, constructing a sequence of tasks that promotes students' own routes to resolving such questions is challenging. This note aims to address this challenge in two ways. First, to illustrate the motivational tactic, the taxicab manifestation of a locus attributed to Apollonius is introduced and a natural question arising from comparison with the analogous Euclidean locus is considered, namely, does the taxicab locus of Apollonius ever coincide with a taxicab circle? Second, a companion sequence of rich undergraduate tasks is elaborated using theoretical design principles, with the tasks culminating in this fundamental geometric question. This note therefore provides a design approach that can be replicated in undergraduate teaching contexts based around similarly motivating mathematical phenomena.     

Regular Steiner polygons

The symmetric difference area functional is minimized for a pair of planar convex polygons. Two solution procedures are outlined: a direct constructive methodology and a support function formulation. Examples illustrate the solution methodology.     

A Higman-Haemers Inequality for Thick Regular Near Polygons

In this note we will generalize the Higman-Haemers inequalities for generalized polygons to thick regular near polygons.     

Regular partitions of (weak) finite generalized polygons

In this paper we define a regular m-partition of a distance regular graph as a partition of the vertex set into m classes, such that the number of vertices of a given class adjacent to a fixed vertex of another class (but possibly the same), is independent of the choice of that vertex in this class. Furthermore, we exhibit a technique to determine exact, discrete or bounding values for the intersection numbers of two such regular partitions of a DRG. As an application, we perform a structural investigation on the substructures of finite generalized polygons and, besides some new results, we give unifying, alternative and more elegant proofs of the results in Offer (J Combin Theory Ser A 97: 184–186, 2002) and Offer (Discrete Math 294: 147–160, 2005). The first author is a Postdoctoral Fellow of the Fund for Scientific Research—Flanders (Belgium) (F.W.O.).     

The Regular Near Polygons of Order (s, 2)

In this note we classify the regular near polygons of order (s, 2).     

An exact construction of digital convex polygons with minimal diameter

Given a natural number n, an exact formula is derived for the minimal possible size MD(n) of a square grid, in which a digital convex n-gon can be inscribed. An exact construction of a digital convex n-gon which can be inscribed into a square grid of size MD(n) is also given.     

正多边形的最优分割问题

记平面边长为1的正m边形为S_m,将S_m剖分成n块:S_(m1),S_(m2),…,S_(mn),这样的剖分称S_m的n剖分,并以T(m,n)表示.以d_(mi)表示区域S_(mi)(i=1,2,…,n)的直径(即区域S_(mi)任意两点之间距离的最大者).记D(m,n)=max{d_(m1),d_(m2),…,d_(mn)}及Ψ(m,n)=■{D(m,n)}.本文将估计Ψ(m,n)的上下界.证明Ψ(6,3)=3/2,Ψ(6,4)=3-3~(1/2),Ψ(6.6)=1,Ψ(6,7)=3/2,估计Ψ(6,n)的渐进性.提出几个猜想.     

正多边形的最优染色分割问题

任意将边长为1的正m边形及其内部每点染n种颜色Y1,Y2,…,Yn中的一种颜色.分别记染色为Y1,Y2,…,Yn的点组成的集合为Sm 1,Sm 2,…,Sm n,这样的剖分称为Sm的n-染色剖分,并以T(m,n)表示.以dm i表示集合Sm i(i=1,2,…,n)的直径.记D(m,n)=m ax{dm 1,dm 2,…,dm n}及θ(m,n)=in fT(m,n){D(m,n)}.证明了θ(6,2)=132,θ(6,3)=32,θ(6,4)=3-3.最后提出了猜想和问题.     

Circular Chromatic Indices of Regular Graphs

The circular chromatic index of a graph G, written , is the minimum r permitting a function such that whenever e and are adjacent. It is known that for any , there is a 3‐regular simple graph G with . This article proves the following results: Assume is an odd integer. For any , there is an n‐regular simple graph G with . For any , there is an n‐regular multigraph G with .     

Intersection of maximal orthogonally starshaped polygons

Let S be a simply connected orthogonal polygon in and let P(S) denote the intersection of all maximal starshaped via staircase paths orthogonal subpolygons in S. Our result: if , then there exists a maximal starshaped via staircase paths orthogonal polygon , such that . As a corollary, P(S) is a starshaped (via staircase paths) orthogonal polygon or empty. The results fail without the requirement that the set S is simply connected. Received 1 March 1999.     

Cyclic polygons with rational sides and area

We generalise the notion of Heron triangles to rational-sided, cyclic n-gons with rational area using Brahmagupta's formula for the area of a cyclic quadrilateral and Robbins' formulæ for the area of cyclic pentagons and hexagons. We use approximate techniques to explore rational area n-gons for n greater than six. Finally, we produce a method of generating non-Eulerian rational area cyclic n-gons for even n and conjecturally classify all rational area cyclic n-gons.     

On a conjecture of Wan about limiting Newton polygons

We show that for a monic polynomial $f(x)$ over a number field K containing a global permutation polynomial of degree >1 as its composition factor, the Newton Polygon of $f\mathrm{mod}\mathfrak{p}$ does not converge for $\mathfrak{p}$ passing through all finite places of K. In the rational number field case, our result is the “only if” part of a conjecture of Wan about limiting Newton polygons.     

Compatible spreads of symmetry in near polygons

In De Bruyn [7] it was shown that spreads of symmetry of near polygons give rise to many other near polygons, the so-called glued near polygons. In the present paper we will study spreads of symmetry in product and glued near polygons. Spreads of symmetry in product near polygons do not lead to new glued near polygons. The study of spreads of symmetry in glued near polygons gives rise to the notion of ‘compatible spreads of symmetry'. We will classify all pairs of compatible spreads of symmetry for the known classes of dense near polygons. All these pairs of spreads can be used to construct new glued near polygons. Postdoctoral Fellow of the Research Foundation-Flanders.     

半群M_n的主因子的极大正则子半群

设Sing_n是[n]上的奇异变换半群,得了变换半群M_n={α∈Sing_n:max{|xα~(-1)}≥|im(α)|(x∈im{α))}的主因子的极大正则子半群的完全分类.     

具有拟理想正则*-断面的正则半群

本文提出了具有正则*-断面正则半群的概念，所给出的例子表明具有拟理想正则*-断面的正则半群类真包含了具有拟理想逆断面的正则半群类和正则*-半群类；最后刻画了具有拟理想正则*-断面的正则半群的结构．     

具有正则*-断面的正则半群的结构

设S是一个正则半群,如果存在一个S的子半群S~*及上的一元运算*满足条件：(1)(?)x∈S,x~*∈S~*∩V(x)；(2)(?)x∈S~*,(x~*)~*=x；(3)(?)x,y∈S,(x~*y)~*=y~*x~(**),(xy~*)~*=y~(xx)x~*则称S~*是S的一个正则*_-断面．本文刻画了具有正则*_-断面的正则半群的结构。     

A bivariate exponential distribution arising in random geometry

Summary In this paper a new bivariate exponential distribution, arising naturally in the theory of Poisson line processes, is studied. The distribution has some interesting and useful properties which renders it suitable for use in statistical modelling work. It is presented in the spirit of adding to the repertoire of bivariate exponential forms. It joins other models, such as those of Downton (1970,J. R. Statist. Soc., B,32, 408–417), Marshall and Olkin (1967,J. Appl. Prob.,4, 291–302) and Nagao and Kadoya (1971,Bulletin of the Disaster Prevention Research Institute,20, 3, 183–215), which have their origins in the theory of stochastic processes.     

Objective tests and latent trait theories

After a discussion about objectivity in measurement, this paper describes some linear and logistic models for the implementation of latent trait theory. The aim is to consider those mathematical and educational issues pertinent to learning more about the topic and using those standardized tests which utilize the Rasch and similar models of assessment.