Results 241 to 250 of about 70,365 (263)

Approximation of unbounded operators by bounded operators and related extremal problems

Russian Mathematical Surveys, 1996
The unit sphere in \(L^p\oplus L^q\) \dots{} In this expository article, dedicated to the memory of Sergei Borisovich Stechkin, the author describes the current state of affairs with regards to the question of approximation of unbounded linear operators by bounded linear operators on a class of elements of a Banach space starting with the formulation ...
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Best approximation of unbounded by bounded operators, and allied problems

Mathematical Notes of the Academy of Sciences of the USSR, 1986
This paper contains the author's abstract of his Doctoral Dissertation. The dissertation is mainly concerned with best approximation in a certain class of elements of an in general unbounded operator by bounded linear operators. This problem is linked, among other extremal problems, with the problem of best restoration of operator values on elements of
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Bounded and Unbounded Linear Operators

1987
Let H be a complex inner product space and let L(H) be the set of all bounded linear operators on H. In this chapter we present some basic facts about the set L(H) as well as about the set of unbounded operators on H. We also present some classes of operators whose structure is better understood, among which we mention the class of hermitian, unitary ...
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A generalized finite difference method based on the Peridynamic differential operator for the solution of problems in bounded and unbounded domains

Computer Methods in Applied Mechanics and Engineering, 2019
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Arman Shojaei, Ugo Galvanetto, Timon Rabczuk, Ali Jenabi, Mirco Zaccariotto   +4 more
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Operator Integrals and Spectral Representations: The Bounded Case

2016
In the traditional Hilbert space quantum mechanics, (bounded or unbounded) selfadjoint operators are taken as physical observables. In the present work a more comprehensive approach is used: observables are represented as normalised positive operator measures. We develop the spectral representation theory of generally unbounded selfadjoint operators in
Paul Busch, Pekka Lahti, Juha-Pekka Pellonpää, Kari Ylinen   +3 more
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Asymptotics of the Fourier transform of the spectral measure for Schr$ouml$dinger operators with bounded and unbounded sparse potentials

Journal of Physics A: Mathematical and General, 2002
Summary: We study the pointwise behaviour of the Fourier transform of the spectral measure for discrete one-dimensional Schrödinger operators with unbounded sparse potentials, particularly with the potentials of the special type, which give rise to the spectra with Hausdorff dimensionality between 1/2 and 1. Operators with bounded sparse potentials are
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Bounded solutions of linear and weakly nonlinear differential equations in a Banach space with an unbounded operator in the linear part

Differential Equations, 2012
The paper presents necessary and sufficient conditions for the existence, on the whole real line, of a weak bounded solution of the following weakly nonlinear differential equation in a Banach space \(\mathbb{B}\) \[ \frac{dx}{dt}=A(t)x(t)+f(t), \;t\in J\subset \mathbb{R}, \] where \(f\) is a Banach-valued continuous and bounded operator and the ...
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Bounded Imaginary Powers and H∞-Calculus of the Stokes Operator in Unbounded Domains

2006
In the present contribution we study the Stokes operator A q = -P q Δ on Lσq (Ω), 1 < q < ∞, where Ω is a suitable bounded or unbounded domain in ℝn, n ≥ 2, with C1,1-boundary. We present some conditions on Ω and the related function spaces and basic equations which guarantee that c + A q for suitable c ∈ ℝ is of positive type and admits a bounded H ...
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Stabilization of Nonautonomous Recurrent Neural Networks With Bounded and Unbounded Delays on Time Scales

IEEE Transactions on Cybernetics, 2020
Qiang Xiao, Tingwen Huang, Zhigang Zeng
exaly  

Admissibility of Unbounded Control Operators

SIAM Journal on Control and Optimization, 1989
George Weiss
exaly