H-张量的判定及其应用

H-张量在科学和工程实际中具有重要应用,但在实际中要判定H-张量是比较困难的.通过构造不同的正对角阵,结合不等式的放缩技巧,给出了一些比较实用的新条件.作为应用,给出判定偶数阶实对称张量正定性的条件,相应数值例子说明了结果的有效性.     

H-张量判定的新迭代准则及其应用

H-张量在科学和工程实际中具有重要应用,但在实际中要判定H-张量是比较困难的.通过构造不同的正对角阵,结合不等式的放缩技巧,给出了H-张量判定的几个新迭代准则.作为应用,给出了判定偶数阶实对称张量正定性的条件,相应的数值例子说明了结果的有效性.     

S~5上仿Blaschke张量的特征值为常数的超曲面

设x:M→S~(n+1)是(n+1)-维单位球面上不含脐点的超曲面,在S~(n+1)的Moebius变换群下浸入x的四个基本不变量是:一个黎曼度量g称为Moebius度量;一个1-形式Φ称为Moebius形式;一个对称的(0,2)张量A称为Blaschke张量和一个对称的(0,2)张量B称为Moebius第二基本形式.对称的(0,2)张量D=A+λB也是Moebius不变量,其中λ是常数,D称为浸入x的仿Blaschke张量.李海中和王长平研究了满足条件:(i)Φ=0;(ii)A+λB+μg=0的超曲面,其中λ和μ都是函数,他们证明了λ和μ都是常数,并且给出了这类超曲面的分类,也就是在Φ=0的条件下D只有一个互异的特征值的超曲面的分类.本文对S~5上满足如下条件的超曲面进行了完全分类:(i)Φ=0,(ii)对某常数λ,D具有常数特征值.     

$\mathcal{H}$-张量的迭代判定及其应用[英文]

H-张量在科学和工程实际中具有重要应用, 但在实际中要判定H-张量是不容易的. 通过构造不同的正对角阵,结合不等式的放缩技巧,给出一些比较实用的H-张量新判别方法.作 为应用,给出判定偶数阶实对称张量正定性的条件, 相应数值例子说明了结果的有效性.     

各向同性超对称Descartes张量

各向同性张量在构造各向同性弹性固体的本构方程时有着极其重要的作用.基于各向同性Descartes张量的表达式并结合超对称张量的性质,探讨了各向同性Descartes张量各标量之间的关系,进而得出了二到六阶各向同性超对称Descartes张量的一般表达式.     

五阶各向同性Descartes张量

研究了五阶各向同性张量的存在性及其一般表示问题,得出了五阶各向同性Ｄｅｓｃａｒｔｅｓ张量的一般表达式。     

S4上仿Blaschke张量的特征值为常数的超曲面

设X：M→S^n＋1州是（n＋1）一维单位球面上不含脐点的超曲面，在S^n＋1的Moebius变换群下浸入x的四个基本不变量是：一个黎曼度量g称为MSbius度量；一个1-形式圣称为Moebius形式；一个对称的（0，2）张量A称为Blaschke张量和一个对称的（0，2）张量B称为MSbius第二基本形式．李海中和王长平研究了满足如下条件的超曲面x：M→S^n＋1：（i）Φ=0；（ii）存在可微函数λ和μ使A＋λg＋μB=0，他们证明了λ和μ都是常数，并且给出了这类超曲面的分类．对称的（0，2）张量A＋λB也是Moebius不变量，称为浸入x的仿Blaschke张量，其中A是常数．因此李海中和王长平也就在Φ=0的条件下给出了A＋λB的特征值全相等的超曲面X：M→s^n＋1州的分类．本文对S^4中满足以下条件的超曲面进行完全分类：（i）Φ=0，（ii）对某一个常数λ，A＋λB具有常数特征值．     

H-张量的迭代判定及其应用（英文）

H-张量在科学和工程实际中具有重要应用,但在实际中要判定H-张量是不容易的.通过构造不同的正对角阵,结合不等式的放缩技巧,给出一些比较实用的H-张量新判别方法.作为应用,给出判定偶数阶实对称张量正定性的条件,相应数值例子说明了结果的有效性.     

实对称张量正定性的判定

实对称张量的正定性在自动控制系统稳定性、多项式全局优化、医疗影像降噪等问题中具有重要的应用价值.通过构造不同的正对角阵和运用不等式的放缩技巧,给出了H-张量新的判别条件.作为应用,给出了偶数阶实对称张量,即偶次齐次多项式正定性的新实用判定方法.相应数值算例表明了结果的有效性.     

一类非对称各向同性张量函数导数的不变表示

将Dui和Chen于2004年提出的求解对称各向同性张量函数导数的方法推广到一类满足可交换条件的非对称各向同性张量函数情况,此类函数比以往研究的更具一般性.在有3个不同特征根时,由可交换性引进张量函数相对应的标量函数,进而求得此类非对称各向同性张量函数及其导数的不变表示形式.在2或3重特征根时,利用求极限的办法给出此类张量函数及其导数的表示形式.     

Limit Laws for Symmetric k-Tensors of Regularly Varying Measures

We consider the asymptotics of certain symmetric k-tensors, the vector analogue of sample moments for i.i.d. random variables. The limiting distribution is operator stable as an element of the vector space of real symmetric k-tensors.     

ℋ-tensors and nonsingular ℋ-tensors

The H-matrices are an important class in the matrix theory, and have many applications. Recently, this concept has been extended to higher order ?-tensors. In this paper, we establish important properties of diagonally dominant tensors and ?-tensors. Distributions of eigenvalues of nonsingular symmetric ?-tensors are given. An ?₊-tensor is semi-positive, which enlarges the area of semi-positive tensor from ?-tensor to ?₊-tensor. The spectral radius of Jacobi tensor of a nonsingular (resp. singular) ?-tensor is less than (resp. equal to) one. In particular, we show that a quasi-diagonally dominant tensor is a nonsingular ?-tensor if and only if all of its principal sub-tensors are nonsingular ?-tensors. An irreducible tensor Ais an ?-tensor if and only if it is quasi-diagonally dominant.     

Programmable criteria for strong $\mathcal {H}$-tensors

Strong \(\mathcal {H}\)-tensors play an important role in identifying positive semidefiniteness of even-order real symmetric tensors. We provide several simple practical criteria for identifying strong \(\mathcal {H}\)-tensors. These criteria only depend on the elements of the tensors; therefore, they are easy to be verified. Meanwhile, a sufficient and necessary condition of strong \(\mathcal {H}\)-tensors is obtained. We also propose an algorithm for identifying the strong \(\mathcal {H}\)-tensors based on these criterions. Some numerical results show the feasibility and effectiveness of the algorithm.     

Criterions for identifying ℋ-tensors

Some new criteria for identifying ?-tensors are obtained. As applications, some sufficient conditions of the positive definiteness for an even-order real symmetric tensor are given, as well as a new eigenvalue inclusion region for tensors is established. It is proved that the new eigenvalue inclusion region is tighter than that of Y. Yang and Q. Yang [SIAM J.Matrix Anal. Appl., 2010, 31: 2517–2530]. Numerical examples are reported to demonstrate the corresponding results.     

Geometry of the Welch bounds

A geometric perspective involving Grammian and frame operators is used to derive the entire family of Welch bounds. This perspective unifies a number of observations that have been made regarding tightness of the bounds and their connections to symmetric k-tensors, tight frames, homogeneous polynomials, and t-designs. In particular, a connection has been drawn between sampling of homogeneous polynomials and frames of symmetric k-tensors. It is also shown that tightness of the bounds requires tight frames. The lack of tight frames of symmetric k-tensors in many cases, however, leads to consideration of sets that come as close as possible to attaining the bounds. The geometric derivation is then extended in the setting of generalized or continuous frames. The Welch bounds for finite sets and countably infinite sets become special cases of this general setting.     

Further results on <Emphasis Type="Italic">B</Emphasis>-tensors with application to location of real eigenvalues

We give a further study on B-tensors and introduce doubly B-tensors that contain B-tensors. We show that they have similar properties, including their decompositions and strong relationship with strictly (doubly) diagonally dominated tensors. As an application, the properties of B-tensors are used to localize real eigenvalues of some tensors, which would be very useful in verifying the positive semi-definiteness of a tensor.     

Partial Differential Equations of Higher Order and Symmetric Positive Systems

In this paper we study the relation between symmetric positive systems and equations of higher order. The main result is: Theorem 1. An equation of second order $L\phi =f$ can be transformed into a symmetric positive system by introducing new unknown functions $u_i=\sum\limits_{j=0}^n {\alpha_ij \varphi _j(i=0,1,\cdots,n),\varphi_0=\varphi_2,\varphi_j=\partial \varphi /\partial x_j}$ iff there exists L_1 of order 1 such that $Re(L_1 \varphi \cdot \bar {L\varphi})=\sum\limits_{i=1}^n{\frac{\partial}{\partial x_i}}+B(\varphi,\varphi)$, where P_i(\varphi,\varphi)(i=1,2,\cdots,n),B(\varphi,\varphi) are differential quadarlic forms and B(\varphi,\varphi) is positive definite. This Theorem can be extended into equations of higher order. Some examples of deducing equations of higher order into symmetric positive systems are given. Finally, we give a counter example which shows that a boundary problem of a symmetric positive system deduced from an equation of higher order is admissible, but its corresponding bounbary problem of the original equation is not well-posed.     

A class of compactly supported orthogonal symmetric complex wavelets with dilation factor 3

When approximation order is an odd positive integer a simple method is given to construct compactly supported orthogonal symmetric complex scaling function with dilation factor 3. Two corresponding orthogonal wavelets, one is symmetric and the other is antisymmetric about origin, are constructed explicitly. Additionally, when approximation order is an even integer 2, we also give a method to construct compactly supported orthogonal symmetric complex wavelets. In the end, there are several examples that illustrate the corresponding results.     

A further method in global differential geometry

We investigate (0, 2)-tensors, which fulfil Codazzi-equations, on closed Riemannian manifolds with nonnegative sectional curvature, and give various applications in global differential geometry.