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Let $D$ be the differentiation operator $Df=f'$ acting on the Fr\'echet space $\H$ of all entire functions in one variable with the standard (compact-open) topology. It is known since 1950's that the set $H(D)$ of hypercyclic vectors for…

Functional Analysis · Mathematics 2012-09-06 Stanislav Shkarin

In this paper, we define and study subspace-diskcyclic operators. We show that subspace-diskcyclicity does not imply to diskcyclicity. We establish a subspace-diskcyclic criterion and use it to find a subspace-diskcyclic operator that is…

Functional Analysis · Mathematics 2015-12-02 Nareen Bamerni , Adem Kılıçman

We study density properties of orbits for a hypercyclic operator $T$ on a separable Banach space $X$, and show that exactly one of the following four cases holds: (1) every vector in $X$ is asymptotic to zero with density one; (2) generic…

Functional Analysis · Mathematics 2026-01-29 Jian Li , Xinsheng Wang , Jianjie Zhao

We solve a number of questions pertaining to the dynamics of linear operators on Hilbert spaces, sometimes by using Baire category arguments and sometimes by constructing explicit examples. In particular, we prove the following results. - A…

Functional Analysis · Mathematics 2017-03-07 Sophie Grivaux , Etienne Matheron , Quentin Menet

For arbitrary closed countable subsets $Z$ of the unit circle examples of topologically mixing operators on Hilbert spaces are given which have a densely spanning set of unimodular eigenvectors with eigenvalues restricted to $Z$. In…

Dynamical Systems · Mathematics 2022-09-19 Hans-Peter Beise , Leonhard Frerick , Jürgen Müller

We describe a class of topological vector spaces admitting a mixing uniformly continuous operator group ${T_t}_{t\in\C^n}$ with holomorphic dependence on the parameter $t$. This result covers those existing in the literature. We also…

Functional Analysis · Mathematics 2012-09-06 Stanislav Shkarin

Let $\mathcal{H}$ be an infinite dimensional real or complex separable Hilbert space. We introduce a special type of a bounded linear operator $T$ and its important relation with invariant subspace problem on $\mathcal{H}$: operator $T$ is…

Dynamical Systems · Mathematics 2021-11-19 Dilan Ahmed , Mudhafar Hama , Jarosław Woźniak , Karwan Jwamer

We characterize weak* closed unital vector spaces of operators on a Hilbert space $H$. More precisely, we first show that an operator system, which is the dual of an operator space, can be represented completely isometrically and weak*…

Operator Algebras · Mathematics 2014-02-26 David P. Blecher , Bojan Magajna

We show that several convolution operators on the space of entire functions, such as the MacLane operator, support a dense hypercyclic algebra that is not finitely generated. Birkhoff's operator also has this property on the space of…

Functional Analysis · Mathematics 2019-03-26 Juan Bès , Dimitris Papathanasiou

Given a densely defined and closed operator $A$ acting on a complex Hilbert space $\mathcal{H}$, we establish a one-to-one correspondence between its closed extensions and subspaces $\mathfrak{M}\subset\mathcal{D}(A^*)$, that are closed…

Functional Analysis · Mathematics 2018-10-12 Christoph Fischbacher

We examine the properties of algebras of linear transformations that leave invariant all subspaces in a totally ordered lattice of subspaces of an arbitrary vector space. We compare our results with those that apply for the corresponding…

Rings and Algebras · Mathematics 2019-02-13 Don Hadwin , K. J. Harrison

The Invariant Subset Problem on the Hilbert space is to know whether there exists a bounded linear operator $T$ on a separable infinite-dimensional Hilbert space $H$ such that the orbit $\{T^{n}x;\ n\ge 0\}$ of every non-zero vector $x\in…

Functional Analysis · Mathematics 2013-01-28 Sophie Grivaux , Maria Roginskaya

It is introduced an open class of linear operators on Banach and Hilbert spaces such that their non-wandering set is an infinite dimensional topologically mixing subspace. In certain cases, the non-wandering set coincides with the whole…

Dynamical Systems · Mathematics 2019-07-29 P. Cirilo , B. Gollobit , E. Pujals

Generalizing the case of a normal operator in a complex Hilbert space, we give a straightforward proof of the non-hypercyclicity of a (bounded or unbounded) scalar type spectral operator $A$ in a complex Banach space as well as of the…

Functional Analysis · Mathematics 2021-02-18 Marat V. Markin

If $T$ is a semibounded self-adjoint operator in a Hilbert space $(H, \, (\cdot , \cdot))$ then the closure of the sesquilinear form $(T \cdot , \cdot)$ is a unique Hilbert space completion. In the non-semibounded case a closure is a…

Functional Analysis · Mathematics 2025-10-14 Andreas Fleige

In this paper we show that every bounded linear operator T on a Hilbert space H has a closed non-trivial invariant subspace.

Functional Analysis · Mathematics 2024-04-09 Per H. Enflo

Based on the success of a well-known method for solving higher order linear differential equations, a study of two of the most important mathematical features of that method, viz. the null spaces and commutativity of the product of…

Functional Analysis · Mathematics 2023-12-12 Richard Kadison , Simon Levin , Zhe Liu

The paper introduces unbounded antilinear operators on Hilbert spaces and develops their fundamental theory. In particular, we establish a closed range theorem, a polar decomposition theorem, and the convexity of the numerical range for…

Functional Analysis · Mathematics 2026-05-25 Arup Majumdar

We first generalize the results of Le\'on and M\"uller [Studia Math. 175(1) 2006] on hypercyclic subspaces to sequences of operators on Fr\'echet spaces with a continuous norm. Then we study the particular case of iterates of an operator T…

Functional Analysis · Mathematics 2014-02-20 Quentin Menet

We completely characterize the finite dimensional subsets A of any separable Hilbert space for which the notion of A-hypercyclicity coincides with the notion of hypercyclicity, where an operator T on a topological vector space X is said to…

Functional Analysis · Mathematics 2018-08-17 S. Charpentier , R. Ernst