On the minimal number of matrices which form a locally hypercyclic, non-hypercyclic tuple

In this paper we extend the notion of a locally hypercyclic operator to that of a locally hypercyclic tuple of operators. We then show that the class of hypercyclic tuples of operators forms a proper subclass to that of locally hypercyclic tuples of operators. What is rather remarkable is that in every finite dimensional vector space over R or C, a pair of commuting matrices exists which forms a locally hypercyclic, non-hypercyclic tuple. This comes in direct contrast to the case of hypercyclic tuples where the minimal number of matrices required for hypercyclicity is related to the dimension of the vector space. In this direction we prove that the minimal number of diagonal matrices required to form a hypercyclic tuple on Rn is n+1, thus complementing a recent result due to Feldman.     

Hereditarily transitive tuples

In this paper, we characterize conditions under which a tuple of continuous operators is hereditarily transitive. Also, we investigate the relation between hypercyclicity and d-dense orbits of a tuple of operators.     

多复变Bergman空间上坐标乘子组的联合酉等价性

本文讨论多复变Ｂｅｒｇｍａｎ空间上坐标乘子组联合酉等价的条件以及与多复变Ｈａｒｄｙ空间上Ｔｏｅｐｌｉｔｚ算子组的关系     

Density-equicontinuity and Density-sensitivity

In this paper we introduce the notions of (Banach) density-equicontinuity and densitysensitivity. On the equicontinuity side, it is shown that a topological dynamical system is densityequicontinuous if and only if it is Banach density-equicontinuous. On the sensitivity side, we introduce the notion of density-sensitive tuple to characterize the multi-variant version of density-sensitivity. We further look into the relation of sequence entropy tuple and density-sensitive tuple both in measuretheoretical and topological setting, and it turns out that every sequence entropy tuple for some ergodic measure on an invertible dynamical system is density-sensitive for this measure; and every topological sequence entropy tuple in a dynamical system having an ergodic measure with full support is densitysensitive for this measure.     

Completely Hyperexpansive Operator Tuples

The notion of a completely hyperexpansive operator on a Hilbert space is generalized to that of a completely hyperexpansive operator tuple, which in some sense turns out to be antithetical to the notion of a subnormal operator tuple with contractive coordinates. The countably many negativity conditions characterizing a completely hyperexpansive operator tuple are closely related to the Levy–Khinchin representation in the theory of harmonic analysis on semigroups. The interplay between the theories of positive and negative definite functions on semigroups forces interesting connections between the classes of subnormal and completely hyperexpansive operator tuples. Further, the several–variable generalization allows for a stimulating interaction with the multiparameter spectral theory.     

Absolute Equivalence and Dirac Operators of Commuting Tuples of Operators

In this paper we define an equivalence relation of operators on Hilbert spaces which we call absolute equivalence. Two operators are called absolutely equivalent if both the absolute value of the operators and their adjoints are unitarily equivalent. We then use the properties of this equivalence relation to study the Koszul complex of a commuting tuple of operators through the Dirac operator of the tuple.     

Complete systems of partial derivatives of entire functions and frequently hypercyclic operators

We find some sufficient conditions for a system of partial derivatives of an entire function to be complete in the space H(C^d)$H({\mathbb{C}}^d)$ of all entire functions of d   variables. As an application of this result we describe new classes of frequently hypercyclic operators on H(C^d)$H({\mathbb{C}}^d)$.     

Outgoing Cuntz scattering system for a coisometric lifting and transfer function

We study a coisometry that intertwines Popescu’s presentations of minimal isometric dilations of a given operator tuple and of a coisometric lifting of the tuple. Using this we develop an outgoing Cuntz scattering system which gives rise to an input–output formalism. A transfer function is introduced for the system. We also compare the transfer function and the characteristic function for the associated lifting.     

Characteristic function for polynomially contractive commuting tuples

In this note, we develop the theory of characteristic function as an invariant for n-tuples of operators. The operator tuple has a certain contractivity condition put on it. This condition and the class of domains in Cn that we consider are intimately related. A typical example of such a domain is the open Euclidean unit ball. Given a polynomial P in C[z₁,z₂,…,zn] whose constant term is zero, all the coefficients are nonnegative and the coefficients of the linear terms are nonzero, one can naturally associate a Reinhardt domain with it, which we call the P-ball (Definition 1.1). Using the reproducing kernel Hilbert space HP(C) associated with this Reinhardt domain in Cn, S. Pott constructed the dilation for a polynomially contractive commuting tuple (Definition 1.2) [S. Pott, Standard models under polynomial positivity conditions, J. Operator Theory 41 (1999) 365-389. MR 2000j:47019]. Given any polynomially contractive commuting tuple T we define its characteristic function θT which is a multiplier. We construct a functional model using the characteristic function. Exploiting the model, we show that the characteristic function is a complete unitary invariant when the tuple is pure. The characteristic function gives newer and simpler proofs of a couple of known results: one of them is the invariance of the curvature invariant and the other is a Beurling theorem for the canonical operator tuple on HP(C). It is natural to study the boundary behaviour of θT in the case when the domain is the Euclidean unit ball. We do that and here essential differences with the single operator situation are brought out.     

非游荡算子半群标准及应用

根据非游荡算子半群的定义得到了非游荡算子半群的几个性质,给出了判定算子半群是非游荡半群的标准,应用给出的标准,在空间C([0,1],C)上讨论了偏微分方程au/at=γx(au/ax)+h(x)u,u(0,x)=f(x)的解半群的性质.     

Decomposing the Secondary Cayley Polytope

The vertices of the secondary polytope of a point configuration correspond to its regular triangulations. The Cayley trick links triangulations of one point configuration, called the Cayley polytope, to the fine mixed subdivisions of a tuple of point configurations. In this paper we investigate the secondary polytope of this Cayley polytope. Its vertices correspond to all regular mixed subdivisions of a tuple of point configurations. We demonstrate that it equals the Minkowski sum of polytopes, which we call mixed secondary polytopes, whose vertices correspond to regular-cell configurations. Received October 1, 1998, and in revised form July 23, 1999.     

Hypercyclicity of special operators on Hilbert function spaces

In this paper we give some sufficient conditions for the adjoint of a weighted composition operator on a Hilbert space of analytic functions to be hypercyclic. This paper is a part of the second author’s Doctoral thesis written at Shiraz University under the direction of the first author.     

由 n×n 上三角Toeplitz矩阵所构成的 超循环矩阵族

在Feldman和Costakis所做的结果的基础上,进一步考虑了超循环算子族的一些问题,设Τ=(T_1,…,T_m)是一组由m个上三角Toeplitz复矩阵构成的矩阵组,给出了一个Τ是超循环的充分必要条件.     

Hypercyclic subspaces in Fréchet spaces

In this note, we show that every infinite-dimensional separable Fréchet space admitting a continuous norm supports an operator for which there is an infinite-dimensional closed subspace consisting, except for zero, of hypercyclic vectors. The family of such operators is even dense in the space of bounded operators when endowed with the strong operator topology. This completes the earlier work of several authors.

     

Topological mixing and Hypercyclicity Criterion for sequences of operators

For a sequence of continuous linear operators on a separable Fréchet space , we discuss necessary conditions and sufficient conditions for to be topologically mixing, and the relations between topological mixing and the Hypercyclicity Criterion. Among them are: 1) topological mixing is equivalent to being hereditarily densely hypercyclic; 2) the Hypercyclicity Criterion with respect to the full sequence implies topological mixing; 3) topological mixing implies the Hypercyclicity Criterion with respect to some sequence that cannot be syndetic in general, and also implies condition (b) of the Hypercyclicity Criterion with respect to the full sequence. Applications to two examples of operators on the Fréchet space of entire functions are also discussed.

     

A short proof of existence of disjoint hypercyclic operators

We give a short proof of existence of disjoint hypercyclic tuples of operators of any given length on any separable infinite dimensional Fréchet space. Similar argument provides disjoint dual hypercyclic tuples of operators of any length on any infinite dimensional Banach space with separable dual.     

Dual disjoint hypercyclic operators

Let E be a separable Fréchet space. The operators T₁,…,Tm are disjoint hypercyclic if there exists x∈E such that the orbit of (x,…,x) under (T₁,…,Tm) is dense in E×?×E. We show that every separable Banach space E admits an m-tuple of bounded linear operators which are disjoint hypercyclic. If, in addition, its dual E^∗ is separable, then they can be constructed such that are also disjoint hypercyclic.     

Mixed-volume computation by dynamic lifting applied to polynomial system solving

The aim of this paper is to present a flexible approach for the efficient computation of the mixed volume of a tuple of polytopes. In order to compute the mixed volume, a mixed subdivision of the tuple of polytopes is needed, which can be obtained by embedding the polytopes in a higher-dimensional space, i.e., by lifting them. Dynamic lifting is opposed to the static approach. This means that one considers one point at a time and only fixes the value of the lifting function when the point really influences the mixed volume. Conservative lifting functions have been developed for this purpose. This provides us with a deterministic manipulation of the lifting for computing mixed volumes, which rules out randomness conditions. Cost estimates for the algorithm are given. The implications of dynamic lifting on polyhedral homotopy methods for the solution of polynomial systems are investigated and applications are presented.     

A second-order pruning step for verified global optimization

We consider pruning steps used in a branch-and-bound algorithm for verified global optimization. A first-order pruning step was given by Ratz using automatic computation of a first-order slope tuple (Ratz, Automatic Slope Computation and its Application in Nonsmooth Global Optimization. Shaker Verlag, Aachen, 1998; J. Global Optim. 14: 365–393, 1999). In this paper, we introduce a second-order pruning step which is based on automatic computation of a second-order slope tuple. We add this second-order pruning step to the algorithm of Ratz. Furthermore, we compare the new algorithm with the algorithm of Ratz by considering some test problems for verified global optimization on a floating-point computer. This paper contains some results from the author’s dissertation [29].