scholarly journals Continuous frames for unbounded operators

2021 ◽  
Vol 6 (2) ◽  
Author(s):  
Giorgia Bellomonte
Keyword(s):  
Hilbert Space ◽  
Unbounded Operator ◽  
Atomic System ◽  
Bounded Operator ◽  
Unbounded Operators ◽  
Linear Bounded Operator ◽  
Continuous Frames ◽  
Densely Defined ◽  
Continuous Setting

AbstractFew years ago Găvruţa gave the notions of K-frame and atomic system for a linear bounded operator K in a Hilbert space $$\mathcal {H}$$ H in order to decompose $$\mathcal {R}(K)$$ R ( K ) , the range of K, with a frame-like expansion. These notions are here generalized to the case of a densely defined and possibly unbounded operator A on a Hilbert space in a continuous setting, thus extending what have been done in a previous paper in a discrete framework.

scholarly journals Closed linear operators with domain containing their range

1984 ◽  
Vol 27 (2) ◽  
pp. 229-233 ◽  
Author(s):  
Schôichi Ôta
Keyword(s):  
Banach Space ◽  
Hilbert Space ◽  
Linear Operator ◽  
Linear Operators ◽  
Closed Linear Operator ◽  
Unbounded Operators ◽  
Densely Defined ◽  
Closed Linear Operators

In connection with algebras of unbounded operators, Lassner showed in [4] that, if T is a densely defined, closed linear operator in a Hilbert space such that its domain is contained in the domain of its adjoint T* and is globally invariant under T and T*,then T is bounded. In the case of a Banach space (in particular, a C*-algebra) weshowed in [6] that a densely defined closed derivation in a C*-algebra with domaincontaining its range is automatically bounded (see the references in [6] and [7] for thetheory of derivations in C*-algebras).

10.—An Abstract Relation for Multiparameter Eigenvalue Problems

1976 ◽  
Vol 74 ◽  
pp. 135-143 ◽  
Author(s):  
A. Källström ◽  
B. D. Sleeman
Keyword(s):  
Hilbert Space ◽  
Operator Equation ◽  
Eigenvalue Problems ◽  
Separable Hilbert Space ◽  
Bounded Operator ◽  
Image Position ◽  
Symmetric Operators ◽  
Densely Defined

SynopsisConsider the multiparameter systemwhere ut is an element of a separable Hilbert space Hi, i = 1, …, n. The operators Sij are assumed to be bounded symmetric operators in Hi and Ai is assumed self-adjoint. In addition consider the operator equationwhere B is densely defined and closed in a separable Hilbert space H and Tj, j = 1, …, n is a bounded operator in H. The problem treated in this paper is to seek an expression for a solution v of (**) in terms of the eigenfunctions of the system (*).

scholarly journals AN UNBOUNDED OPERATOR WITH SPECTRUM IN A STRIP AND MATRIX DIFFERENTIAL OPERATORS

2021 ◽  
pp. 1-8
Author(s):  
MICHAEL GIL’
Keyword(s):  
Hilbert Space ◽  
Unbounded Operator ◽  
Differential Operators ◽  
Bounded Operator ◽  
Linear Operators ◽  
Regular Matrix ◽  
Horizontal Strip ◽  
Matrix Differential Operators ◽  
Matrix Differential ◽  
Unbounded Linear Operators

Abstract Let A and $\tilde A$ be unbounded linear operators on a Hilbert space. We consider the following problem. Let the spectrum of A lie in some horizontal strip. In which strip does the spectrum of $\tilde A$ lie, if A and $\tilde A$ are sufficiently ‘close’? We derive a sharp bound for the strip containing the spectrum of $\tilde A$ , assuming that $\tilde A-A$ is a bounded operator and A has a bounded Hermitian component. We also discuss applications of our results to regular matrix differential operators.

scholarly journals General Iterative Algorithms for Hierarchical Fixed Points Approach to Variational Inequalities

2012 ◽  
Vol 2012 ◽  
pp. 1-20
Author(s):  
Nopparat Wairojjana ◽  
Poom Kumam
Keyword(s):  
Hilbert Space ◽  
Fixed Point ◽  
Variational Inequality ◽  
Bounded Operator ◽  
Iterative Algorithms ◽  
Metric Projection ◽  
Fixed Point Problem ◽  
Point Problem ◽  
Linear Bounded Operator ◽  
New Methods

This paper deals with new methods for approximating a solution to the fixed point problem; findx̃∈F(T), whereHis a Hilbert space,Cis a closed convex subset ofH,fis aρ-contraction fromCintoH,0<ρ<1,Ais a strongly positive linear-bounded operator with coefficientγ̅>0,0<γ<γ̅/ρ,Tis a nonexpansive mapping onC,andPF(T)denotes the metric projection on the set of fixed point ofT. Under a suitable different parameter, we obtain strong convergence theorems by using the projection method which solves the variational inequality〈(A-γf)x̃+τ(I-S)x̃,x-x̃〉≥0forx∈F(T), whereτ∈[0,∞). Our results generalize and improve the corresponding results of Yao et al. (2010) and some authors. Furthermore, we give an example which supports our main theorem in the last part.

scholarly journals On Injectivity of an Integral Operator Connected to Riemann Hypothesis

2021 ◽  
Author(s):  
Dumitru Adam
Keyword(s):  
Hilbert Space ◽  
Integral Operator ◽  
Hilbert Spaces ◽  
Separable Hilbert Space ◽  
Bounded Operator ◽  
Fractional Part ◽  
Positive Definite ◽  
Its Sequence ◽  
Bounded Operators ◽  
Linear Bounded Operator

Abstract In 1993, Alcantara-Bode showed ([2]) that Riemann Hypothesisholds if and only if the integral operator on the Hilbert space L2(0; 1)having the kernel function defined by the fractional part of (y/x), isinjective. Since then, the injectivity of the integral operator used inequivalent formulation of RH has not been addressed nor has beendissociated from RH.We provided in this paper methods for investigating the injectivityof linear bounded operators on separable Hilbert spaces using theirapproximations on dense families of subspaces.On the separable Hilbert space L2(0,1), an linear bounded operator(or its associated Hermitian), strict positive definite on a dense familyof including approximation subspaces in built on simple functions, isinjective if the rate of convergence of its sequence of injectivity pa-rameters on approximation subspaces is inferior bounded by a not nullconstant, that is the case with the Beurling - Alcantara-Bode integraloperator.We applied these methods to the integral operator used in RHequivalence proving its injectivity.

scholarly journals Modified Iterative Algorithms for Nonexpansive Mappings

2009 ◽  
Vol 2009 ◽  
pp. 1-11 ◽  
Author(s):  
Yonghong Yao ◽  
Muhammad Aslam Noor ◽  
Syed Tauseef Mohyud-Din
Keyword(s):  
Hilbert Space ◽  
Approximate Solution ◽  
Real Number ◽  
Real Hilbert Space ◽  
Nonexpansive Mappings ◽  
Bounded Operator ◽  
Iterative Algorithms ◽  
Contractive Mapping ◽  
Linear Bounded Operator ◽  
Special Cases

Let H be a real Hilbert space, let S, T be two nonexpansive mappings such that F(S)∩F(T)≠∅, let f be a contractive mapping, and let A be a strongly positive linear bounded operator on H. In this paper, we suggest and consider the strong converegence analysis of a new two-step iterative algorithms for finding the approximate solution of two nonexpansive mappings as xn+1=βnxn+(1−βn)Syn, yn=αnγf(xn)+(I−αnA)Txn, n≥0 is a real number and {αn}, {βn} are two sequences in (0,1) satisfying the following control conditions: (C1) lim⁡n→∞ αn=0, (C3) 0<lim⁡inf⁡n→∞ βn≤lim⁡sup⁡n→∞ βn<1, then ‖xn+1−xn‖→0. We also discuss several special cases of this iterative algorithm.

scholarly journals An inequality for similarity condition numbers of unbounded operators with Schatten - von Neumann Hermitian components

Filomat ◽  
2016 ◽  
Vol 30 (13) ◽  
pp. 3415-3425 ◽  
Author(s):  
Michael Gil’
Keyword(s):  
Hilbert Space ◽  
Unbounded Operator ◽  
Differential Operators ◽  
Separable Hilbert Space ◽  
Normal Operator ◽  
Condition Numbers ◽  
Unbounded Operators ◽  
Similarity Condition ◽  
Von Neumann ◽  
Operator Functions

Let H be a linear unbounded operator in a separable Hilbert space. It is assumed the resolvent of H is a compact operator and H ? H* is a Schatten - von Neumann operator. Various integro-differential operators satisfy these conditions. Under certain assumptions it is shown that H is similar to a normal operator and a sharp bound for the condition number is suggested. We also discuss applications of that bound to spectrum perturbations and operator functions.

A BOUND FOR SIMILARITY CONDITION NUMBERS OF UNBOUNDED OPERATORS WITH HILBERT–SCHMIDT HERMITIAN COMPONENTS

2014 ◽  
Vol 97 (3) ◽  
pp. 331-342 ◽  
Author(s):  
MICHAEL GIL’
Keyword(s):  
Hilbert Space ◽  
Condition Number ◽  
Unbounded Operator ◽  
Differential Operators ◽  
Normal Operator ◽  
Condition Numbers ◽  
Unbounded Operators ◽  
Similarity Condition ◽  
Operator Functions ◽  
Schmidt Operator

AbstractLet $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}H$ be a linear unbounded operator in a Hilbert space. It is assumed that the resolvent of $H$ is a compact operator and $H-H^*$ is a Hilbert–Schmidt operator. Various integro-differential operators satisfy these conditions. It is shown that $H$ is similar to a normal operator and a sharp bound for the condition number is suggested. We also discuss applications of that bound to spectrum perturbations and operator functions.

A different approach to unbounded operator algebras

1989 ◽  
Vol 106 (1) ◽  
pp. 125-141
Author(s):  
M. A. Hennings
Keyword(s):  
Hilbert Space ◽  
Unbounded Operator ◽  
Operator Algebras ◽  
Inner Product ◽  
Unbounded Operators ◽  
Graph Topology ◽  
Dense Domain ◽  
The One ◽  
Locally Convex Topology ◽  
Locally Convex

When considering *-algebras of unbounded operators, the usual approach is perhaps the one to be expected. One starts with a Hilbert space , and then defines a common dense domain X associated with some *-algebra of unbounded operators on . The algebra is then used to define a locally convex topology (the graph topology) on X, with respect to which the inner product on X is continuous, and this in turn defines a variety of topologies on , which are then studied.

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