Trace forms, kronecker sums, and the shuffle matrix

The trace map on the ring of square matrices with entries in a field can be used to define various quadratic forms on this ring. This paper makes a study of some of these forms and in particular the "scaled trace forms" are shown to have a symmetric matrix representation involving both Kronecker sums and the shuffle matrix.     

On bilinear forms in normal variables

Bilinear forms in normal variables when the matrices of the forms are rectangular are considered. Explicit expressions for the cumulants, joint cumulants and joint cumulants of bilinear and quadratic forms are given. Necessary and sufficient conditions are established for the independence of two bilinear forms as well as a bilinear and a quadratic form. Special cases are shown to agree with known results.     

On hermitian trace forms over hilbertian fields

Let k be a field of characteristic different from 2. Let be a finite separable extension with a {\it k}-linear involution . For every -symmetric element , we define a hermitian scaled trace form by . If , it is called a hermitian trace form. In the following, we show that every even-dimensional quadratic form over a hilbertian field, which is not isomorphic to the hyperbolic plane, is isomorphic to a hermitian scaled trace form. Then we give a characterization of Witt classes of hermitian trace forms over some hilbertian fields. Received August 3, 1999; in final form January 10, 2000 / Published online March 12, 2001     

Norm equalities and inequalities for three circulant operator matrices

In this paper, three new circulant operator matrices, scaled circulant operator matrices, diag-circulant operator matrices and retrocirculant operator matrices, are given respectively. Several norm equalities and inequalities for these operator matrices are proved. We show the special cases for norm equalities and inequalities, such as the usual operator norm and the Schatten p-norm. Pinching type inequality is also given for weakly unitarily invariant norms. These results are closely related to the nice structure of these special operator matrices. Furthermore, some special cases and specific examples are also considered.     

Modular independence and generator matrices for codes over $${\mathbb {Z}_m}$$

We introduce a new notion of modular independence to define bases and the generator matrices for the codes over the ring of integers of general modulus m. We define standard forms for such generator matrices, and discuss how to find such forms and the parity check matrices.      

Strong regularity of parametric interval matrices

Several verifiable sufficient and necessary conditions for strong regularity of parametric interval matrices are given. The conditions are formulated in terms of the spectral radius, positive definiteness and eigenvalues of certain real matrices and a scaled maximum norm.     

Canonical forms for unitary congruence and *congruence

We use methods of the general theory of congruence and *congruence for complex matrices – regularization and cosquares – to determine a unitary congruence canonical form (respectively, a unitary *congruence canonical form) for complex matrices A such that āA (respectively, A ²) is normal. As special cases of our canonical forms, we obtain – in a coherent and systematic way – known canonical forms for conjugate normal, congruence normal, coninvolutory, involutory, projection, λ-projection, and unitary matrices. But we also obtain canonical forms for matrices whose squares are Hermitian or normal, and other cases that do not seem to have been investigated previously. We show that the classification problems under (a) unitary *congruence when A ³ is normal, and (b) unitary congruence when AāA is normal, are both unitarily wild, so these classification problems are hopeless.     

Level-m scaled circulant factor matrices over the complex number field and the quaternion division algebra

The level-m scaled circulant factor matrix over the complex number field is introduced. Its diagonalization and spectral decomposition and representation are discussed. An explicit formula for the entries of the inverse of a level-m scaled circulant factor matrix is presented. Finally, an algorithm for finding the inverse of such matrices over the quaternion division algebra is given.     

Trace forms of abelian extensions of number fields of type (1, 0)

This article is concerned with describing certain bilinear forms associated with finite abelian extensions N|K of an algebraic number field K. These abelian trace forms are described up to Witt equivalence, that is, they are described as elements in the Witt ring W(K). When the base field K has exactly one dyadic prime and no real embeddings, it is shown that the Witt class of every abelian trace form over K is a product of Witt classes of five specified types.     

Convexity Conditions and the Legendre-Fenchel Transform for the Product of Finitely Many Positive Definite Quadratic Forms

While the product of finitely many convex functions has been investigated in the field of global optimization, some fundamental issues such as the convexity condition and the Legendre-Fenchel transform for the product function remain unresolved. Focusing on quadratic forms, this paper is aimed at addressing the question: When is the product of finitely many positive definite quadratic forms convex, and what is the Legendre-Fenchel transform for it? First, we show that the convexity of the product is determined intrinsically by the condition number of so-called ‘scaled matrices’ associated with quadratic forms involved. The main result claims that if the condition number of these scaled matrices are bounded above by an explicit constant (which depends only on the number of quadratic forms involved), then the product function is convex. Second, we prove that the Legendre-Fenchel transform for the product of positive definite quadratic forms can be expressed, and the computation of the transform amounts to finding the solution to a system of equations (or equally, finding a Brouwer’s fixed point of a mapping) with a special structure. Thus, a broader question than the open “Question 11” in Hiriart-Urruty (SIAM Rev. 49, 225–273, 2007) is addressed in this paper.     

二、三阶可逆矩阵可以相似对角化的几何条件

从几何的角度给出了特征值不含1的二、三阶可逆矩阵可以相似对角化的一个充分条件和二、三阶可逆矩阵可以相似对角化的一个充分必要条件.     

关于厄米特矩阵乘积特征值的讨论

讨论厄米特矩阵乘积的特征值 ,推广了文 [1 ]的结果 .指出了文 [2 ]中的一个错误 ,给出了关于迹的一个不等式 .     

四阶正则微分算子耦合自共轭边界条件的基本标准型

本文利用新的方法给出了4阶正则微分算子耦合自共轭边界条件的基本标准型,新标准型中的4个分块小矩阵为对称矩阵,且其行列式的模为1.这与2阶微分算子耦合边界条件的标准型极为类似,这为给出一般的高阶微分算子自共轭边界条件标准型提供了新的思路.     

Duality in conjugate gradient methods

In this paper we show that if the step (displacement) vectors generated by the preconditioned conjugate gradient algorithm are scaled appropriately they may be used to solve equations whose coefficient matrices are the preconditioning matrices of the original equations. The dual algorithms thus obtained are shown to be equivalent to the reverse algorithms of Hegedüs and are subsequently generalised to their block forms. It is finally shown how these may be used to construct dual (or reverse) algorithms for solving equations involving nonsymmetric matrices using only short recurrences, and reasons are suggested why some of these algorithms may be more numerically stable than their primal counterparts. This revised version was published online in June 2006 with corrections to the Cover Date.     

关于矩阵迹的一些不等式

对由Bellman不等式推导的两个关于实正定对称矩阵迹的不等式进行了进一步的推广,并得到了一系列的关于矩阵迹的不等式。     

The modern origin of matrices and their applications

This paper deals with the modern development of matrices, linear transformations, quadratic forms and their applications to geometry and mechanics, eigenvalues, eigenvectors and characteristic equations with applications. Included are the representations of real and complex numbers, and quaternions by matrices, and isomorphism in order to show that matrices form a ring in abstract algebra. Some special matrices, including Hilbert’s matrix, Toeplitz’s matrix, Pauli’s and Dirac’s matrices in quantum mechanics, and Einstein’s Pythagorean formula are discussed to illustrate diverse applications of matrix algebra. Included also is a modern piece of information that puts mathematics, science and mathematics education professionals at the forefront of advanced study and research on linear algebra and its applications.     

Sums of nilpotent matrices

We study matrices over general rings which are sums of nilpotent matrices. We show that over commutative rings all matrices with nilpotent trace are sums of three nilpotent matrices. We characterize 2-by-2 matrices with integer entries which are sums of two nilpotents via the solvability of a quadratic Diophantine equation. Some exemples in the case of matrices over noncommutative rings are given.     

Generating Jacobi Forms

In this paper we explore the relationship between vector-valued modular forms and Jacobi forms and give explicit relations over various congruence subgroups. The main result is that a Jacobi form of square-free index on the full Jacobi group is uniquely determined by any of the associated vector components. In addition, an explicit construction is given to determine the other vector components from this single component. In other words, we give an explicit construction of a Jacobi form from a subset of its Fourier coefficients. This leads to results about how the transformation properties are affected by congruence restrictions on the Fourier expansion. 2000 Mathematics Subject Classification: Primary—11F50; Secondary—11F30     

BILINEAR FORMS AND LINEAR CODES

Abraham Lempel et al^[1] made a connection between linear codes and systems of bilinear forms over finite fields. In this correspondence, a new simple proof of a theorem in [1] is presented; in addition, the encoding process and the decoding procedure of RS codes are simplified via circulant matrices. Finally, the results show that the correspondence between bilinear forms and linear codes is not unique.     

A Closed Formula for the Moore-Penrose Generalized Inverse of a Complex Matrix of Given Rank

For the Moore-Penrose generalized inverse of complex matrices, we establish closed forms valid on each set of matrices of given rank. These expressions are matrices of rational functions of the matrix coefficients and their complex conjugates, so that it is seen explicitly and constructively that taking the Moore-Penrose inverse is a real-analytic operation when restricted to the subsets of matrices of given rank.