n维空间正交张量的典则表示和自由度公式

本文借助于正交张量特征值的特性,采用剖分的方法.利用二维正交张量典则表示,很快就构造出一般n维欧氏空间上的正交张量的典则表示.利用Cayley-Hamilton定理,求得了正交张量各主不变量之间的相关方程,从而使得正交张量特征根的求解只需要在一个阶数不大于空间维数n的一半的代数方程上进行.本文还给出了正交张量的独立参数个数——自由度的计算公式.     

欧氏空间中等角基的性质

等角基是正交基的推广,等角基具有和正交基相似的性质,因此研究等角基的性质能够为研究欧氏空间提供一种工具,加深对欧氏空间的了解．本文主要把n维欧氏空间中正交基的一些性质推广到等角基上,得到了五个关于等角基性质的定理．     

欧氏空间中等角基的性质

等角基是正交基的推广,等角基具有和正交基相似的性质,因此研究等角基的性质能够为研究欧氏空间提供一种工具,加深对欧氏空间的了解.本文主要把n维欧氏空间中正交基的一些性质推广到等角基上,得到了五个关于等角基性质的定理.     

Hausdorff Dimension and Non-degenerate Families of Projections

We study parameterized families of orthogonal projections for which the dimension of the parameter space is strictly less than that of the Grassmann manifold. We answer the natural question of how much the Hausdorff dimension may decrease by verifying the best possible lower bound for the dimension of almost all projections of a finite measure. We also show that a similar result is valid for smooth families of maps from the n-dimensional Euclidean space to the m-dimensional one.     

On proulx's four exceptional toroidal groups

V. K. Proulx has proved that every finite group having a Cayley graph embeddable in the torus is, with four unresolved exceptions, a quotient of a Euclidean space group. It was conjectured that these four unresolved groups are not exceptional, that they in fact are Euclidean space-group quotients. It is shown here that one is not exceptional, but the other three are.     

On Hypereuclidean Manifolds

We show that the universal cover of an aspherical manifold whose fundamental groups has finite asymptotic dimension in sense of Gromov is hypereuclidean after crossing with some Euclidean space     

On a Generalization of the Hermite Constant

We report some results on the theory of quasiperiodic sphere packings controlled by a finite group G in the n-dimensional Euclidean space, constructed by means of an higher dimensional Euclidean space which contains G-invariant lattices. A generalization of the Hermite constant is used to find upper bounds of the density.     

Orthogonal sequences and regularity of embeddings into finite-dimensional spaces

This paper focuses on the regularity of linear embeddings of finite-dimensional subsets of Hilbert and Banach spaces into Euclidean spaces. We study orthogonal sequences in a Hilbert space H, whose elements tend to zero, and similar sequences in the space c₀ of null sequences. The examples studied show that the results due to Hunt and Kaloshin (Regularity of embeddings of infinite-dimensional fractal sets into finite-dimensional spaces, Nonlinearity 12 (1999) 1263-1275) and Robinson (Linear embeddings of finite-dimensional subsets of Banach spaces into Euclidean spaces, Nonlinearity 22 (2009) 711-728) for subsets of Hilbert and Banach spaces with finite box-counting dimension are asymptotically sharp. An analogous argument allows us to obtain a lower bound for the power of the logarithmic correction term in an embedding theorem proved by Olson and Robinson (Almost bi-Lipschitz embeddings and almost homogeneous sets, Trans. Amer. Math. Soc. 362 (1) (2010) 145-168) for subsets X of Hilbert spaces when X−X has finite Assouad dimension.     

An acyclicity theorem for cell complexes ind dimension

LetC be a cell complex ind-dimensional Euclidean space whose faces are obtained by orthogonal projection of the faces of a convex polytope ind+ 1 dimensions. For example, the Delaunay triangulation of a finite point set is such a cell complex. This paper shows that the in_front/behind relation defined for the faces ofC with respect to any fixed viewpointx is acyclic. This result has applications to hidden line/surface removal and other problems in computational geometry.Research reported in this paper was supported by the National Science Foundation under grant CCR-8714565     

Rigidity in the class of orientable compact surfaces of minimal total absolute curvature

Consider an orientable compact surface in three-dimensional Euclidean space with minimum total absolute curvature. If the Gaussian curvature changes sign to finite order and satisfies a nondegeneracy condition along closed asymptotic curves, we show that any other isometric surface differs by at most a Euclidean motion.     

Finite rank kernels for multi-task learning

Motivated by the importance of kernel-based methods for multi-task learning, we provide here a complete characterization of multi-task finite rank kernels in terms of the positivity of what we call its associated characteristic operator. Consequently, we are led to establishing that every continuous multi-task kernel, defined on a cube in an Euclidean space, not only can be uniformly approximated by multi-task polynomial kernels, but also can be extended as a multi-task kernel to all of the Euclidean space. Finally, we discuss the interpolation of multi-task kernels by multi-task finite rank kernels.     

Bezoutians, Euclidean Algorithm, and Orthogonal Polynomials

We prove a quadratic expression for the Bezoutian of two univariate polynomials in terms of the remainders for the Euclidean algorithm. In case of two polynomials of the same degree, or of consecutive degrees, this allows us to interpret their Bezoutian as the Christoffel- Darboux kernel for a finite family of orthogonal polynomials, arising from the Euclidean algorithm. We give orthogonality properties of remainders, and reproducing properties of Bezoutians. Received December 13, 2004     

MULTIFRACTAL DECOMPOSITION OF FRACTALS WITH FINITE MEMORY

The authors study recursive structures with ＂finite memory＂ in Euclidean matric space and the multifractal decomposition of the corresponding fractals. For any two positive numbers q,β, and such a recursive structure, a linear operator V^q,β in finite dimensional space is defined. The multifractal spectrum is given by the spectral radius of Vq,^β.     

A weak characterisation of the Delaunay triangulation

We consider a new construction, the weak Delaunay triangulation of a finite point set in a metric space, which contains as a subcomplex the traditional (strong) Delaunay triangulation. The two simplicial complexes turn out to be equal for point sets in Euclidean space, as well as in the (hemi)sphere, hyperbolic space, and certain other geometries. There are weighted and approximate versions of the weak and strong complexes in all these geometries, and we prove equality theorems in those cases also. On the other hand, for discrete metric spaces the weak and strong complexes are decidedly different. We give a short empirical demonstration that weak Delaunay complexes can lead to dramatically clean results in the problem of estimating the homology groups of a manifold represented by a finite point sample.      

Rational invariants of certain orthogonal groups over finite fields of characteristic two

In this article we establish the conjecture of Huah Chu [8] on modular rational invariants of finite orthogonal groups over finite fields of characteristic two.

We prove that the invariant subfield of two cases non-singular, and singular quadratic space over a finite field of characteristic two is purely transcendental.     

A New Euclidean Tight 6-Design

Euclidean t-designs, which are finite weighted subsets of Euclidean space, were defined by Neumaier-Seidel (1988). A tight t-design is defined as a t-design whose cardinality is equal to the known natural lower bound. In this paper, we give a new Euclidean tight 6-design in ${\mathbb{R}^{22}}$ . Furthermore, we also show its uniqueness up to similar transformation fixing the origin. This design has the structure of coherent configuration, which was defined by Higman, and is obtained from the properties of general permutation groups. We also show that the design is obtained by combining two orbits of McLaughlin simple group.     

Coding‐theoretic constructions for (t,m,s)‐nets and ordered orthogonal arrays

(t,m,s)‐nets are point sets in Euclidean s‐space satisfying certain uniformity conditions, for use in numerical integration. They can be equivalently described in terms of ordered orthogonal arrays, a class of finite geometrical structures generalizing orthogonal arrays. This establishes a link between quasi‐Monte Carlo methods and coding theory. The ambient space is a metric space generalizing the Hamming space of coding theory. We denote it by NRT space (named after Niederreiter, Rosenbloom and Tsfasman). Our main results are generalizations of coding‐theoretic constructions from Hamming space to NRT space. These comprise a version of the Gilbert‐Varshamov bound, the (u,u+υ)‐construction and concatenation. We present a table of the best known parameters of q‐ary (t,m,s)‐nets for qε{2,3,4,5} and dimension m≤50. © 2002 Wiley Periodicals, Inc. J Combin Designs 10: 403–418, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10015     

A Weyl type formula for Fourier spectra and frames

We prove qualitative and quantitative results concerning the asymptotic density in dilates of centered convex bodies of the frequency vectors of orthogonal exponential bases and frames associated to bounded domains in Euclidean space.

     

Operator self similar stochastic processes in Rd

Operator self similar stochastic processes taking values in a finite dimensional Euclidean space are introduced and some of their properties are studied.     

A recursive algorithm for finding the minimum norm point in a polytope and a pair of closest points in two polytopes

For a given pair of finite point setsP andQ in some Euclidean space we consider two problems: Problem 1 of finding the minimum Euclidean norm point in the convex hull ofP and Problem 2 of finding a minimum Euclidean distance pair of points in the convex hulls ofP andQ. We propose a finite recursive algorithm for these problems. The algorithm is not based on the simplicial decomposition of convex sets and does not require to solve systems of linear equations.