Multipliers of elementary operators and comparison of row and column space Schatten p norms

Sharp upper estimates for the norm of the weighted elementary operator of the form , acting from one symmetrically normed ideal of compact Hilbert space operators to another, are given. Particularly, we relate the norm of with norms of and on the appropriate domains and co-domains.     

A condition for diagonalization modulo arbitrary norm ideals

We give a spectral condition which is sufficient for the simultaneous diagonalization of a commuting tuple of self-adjoint operators modulo a given norm ideal. For diagonalization modulo certain norm ideals this condition is also necessary, while for other norm ideals this condition seems to be close to being necessary. Moreover, this condition is easy to verify in applications.     

Rank Reducing Matrix Norms

We consider approximation numbers for some norms on matrices, and look at the question when a closest rank h p approximant can be chosen to reduce the rank of a matrix by p . If the latter is always possible, we call the norm rank p reducing. It is easily seen that any unitarily invariant norm is rank p reducing. We show that any absolute norm on $\shadC^{n \times m}$ is rank n m 1 reducing and that the numerical radius norm on $ \shadC^{n\times n}$ is rank n m 1 reducing as well. Non-examples and computations of approximation numbers are also presented.     

Hadamard product submultiplicativity of certain induced norms

In this paper we ask which norms on M_d induced by an absolute vector norm are sub-multiplicative with respect to the Hadamard product. We provide a simple necessary condition for submultiplicativity. We demonstrate that each norm on M_d induced by an l_p norm Hadamard submultiplicative and that the norms induced by certain polyhedral norms are Hadamard submultiplicative. We also consider some related inequalities.     

Hadamard product submultiplicativity of certain induced norms

In this paper we ask which norms on M_d induced by an absolute vector norm are sub-multiplicative with respect to the Hadamard product. We provide a simple necessary condition for submultiplicativity. We demonstrate that each norm on M_d induced by an l_p norm Hadamard submultiplicative and that the norms induced by certain polyhedral norms are Hadamard submultiplicative. We also consider some related inequalities.     

Pinchings and Norms of Scaled Triangular Matrices

Suppose U is an upper-triangular matrix, and D a nonsingular diagonal matrix whose diagonal entries appear in nondescending order of magnitude down the diagonal. It is proved that $$\|D^{-1}UD\|\ge\|U\|$$ for any matrix norm that is reduced by a pinching. In addition to known examples -weakly unitarily invariant norms - we show that any matrix norm defined by $$\| A \|^{\underline{\underline {{\rm def}}} } \mathop {\max }\limits_{x \ne 0,y \ne 0} {{{\mathop{\rm Re}\nolimits} (x^*Ay)} \over {\phi (x)\psi (y)}},$$ where θ (.) and y (.) are two absolute vector norms, has this property. This includes l p operator norms as a special case.     

Norm expansion along a zero variety

The reproducing kernel function of a weighted Bergman space over domains in Cd is known explicitly in only a small number of instances. Here, we introduce a process of orthogonal norm expansion along a subvariety of (complex) codimension 1, which also leads to a series expansion of the reproducing kernel in terms of reproducing kernels defined on the subvariety. The problem of finding the reproducing kernel is thus reduced to the same kind of problem when one of the two entries is on the subvariety. A complete expansion of the reproducing kernel may be achieved in this manner. We carry this out in dimension d=2 for certain classes of weighted Bergman spaces over the bidisk (with the diagonal z₁=z₂ as subvariety) and the ball (with z₂=0 as subvariety), as well as for a weighted Bargmann-Fock space over C² (with the diagonal z₁=z₂ as subvariety).     

A characterization of maximum norms of commutators of positive contractions

In this note, we give a characterization of a pair (A,B) of positive contractions with commutator AB−BA of maximum possible norm. A necessary and sufficient condition is that either or its complex conjugate is in the closure of the numerical range of AB.     

The Equivalence of BMOA and VMOA on the Unit Ball of C n

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Norm equality for a basic elementary operator

Let be the algebra of bounded linear operators on a Hilbert space H. For , define the elementary operator M_A,B by M_A,B(X)=AXB (). We give necessary and sufficient conditions for any pair of operators A and B to satisfy the equation ‖I+M_A,B‖=1+‖A‖‖B‖, where I is the identity operator on H.     

Norm Attainability of Elementary Operators and Derivations

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Norms of composition operators with rational symbol

We compute the norms of composition operators with rational symbols that satisfy certain properties, extending Christopher Hammond's methods on operators with linear fractional symbols. This leads to a host of new examples of composition operators whose norms are calculable.     

列压缩算子的不动点定理及其应用

本文在无连续性及紧性的假设情况下,讨论了u0-凹的列压缩算子及一类混合单调算子的不动点定理,并给出了在积分方程中的应用.     

Norms of commutators of self-adjoint operators

In this note, the estimate of norms of commutators of self-adjoint operators is established.     

Norm inequalities for commutators of positive operators and applications

Let X, Y, and Z be operators on a Hilbert space such that X and Z are positive. It is shown that

Equivalence of anchored and ANOVA spaces via interpolation

We consider weighted anchored and ANOVA spaces of functions with first order mixed derivatives bounded in $L_p$. Recently, Hefter, Ritter and Wasilkowski established conditions on the weights in the cases $p=1$ and $p=\infty$ which ensure equivalence of the corresponding norms uniformly in the dimension or only polynomially dependent on the dimension. We extend these results to the whole range of $p\in [1,\infty ]$. It is shown how this can be achieved via interpolation.     

具有确定非零对角元个数的布尔矩阵广义幂敛指数的极矩阵

设A是周期为P的n阶布尔矩阵,1≤i≤n,A的广义幂敛指数k(A,i)是使得Ak和Ak+p有i行对应相等的最小非负整数k.本文刻画了恰含d(1≤d≤n)个非零对角元的n阶布尔矩阵的广义幂敛指数的极矩阵.     

Norm Inequalities for Potential-Type Operators in Homogeneous Spaces

In this paper, we obtain a characterization of the positive Borel measures on a homogeneous space X, for which the trace inequality holds for any f ≥. Here I_Φ is a general potential type kernel, and 1 ≤ q < p < +∞. The characterization is given in terms of a generalized Wolff's potential.     

Local and global norm comparison theorems for solutions to the nonhomogeneous A-harmonic equation

We establish local and global norm inequalities for solutions of the nonhomogeneous A-harmonic equation A(x,g+du)=h+d^?v for differential forms. As applications of these inequalities, we prove the Sobolev-Poincaré type imbedding theorems and obtain Lp-estimates for the gradient operator ∇ and the homotopy operator T from the Banach space Ls(D,Λl) to the Sobolev space W1,s(D,Λl−1), l=1,2,…,n. These results can be used to study both qualitative and quantitative properties of solutions of the A-harmonic equations and the related differential systems.