Operators In Spaces Research Articles

A novel algorithm with an inertial technique for fixed points of nonexpansive mappings and zeros of accretive operators in Banach spaces

<abstract><p>The purpose of this paper was to prove that a novel algorithm with an inertial approach, used to generate an iterative sequence, strongly converges to a fixed point of a nonexpansive mapping in a real uniformly convex Banach space with a uniformly Gâteaux differentiable norm. Furthermore, zeros of accretive mappings were obtained. The proposed algorithm has been implemented and tested via numerical simulation in MATLAB. The simulation results showed that the algorithm converges to the optimal configurations and shows the effectiveness of the proposed algorithm.</p></abstract>

Jointly $ A $-hyponormal $ m $-tuple of commuting operators and related results

<p>In this paper, we aim to investigate the class of jointly hyponormal operators related to a positive operator $ A $ on a complex Hilbert space $ \mathcal{X} $, which is called jointly $ A $-hyponormal. This notion was first introduced by Guesba et al. in [Linear and Multilinear Algebra, 69(15), 2888–2907] for $ m $-tuples of operators that admit adjoint operators with respect to $ A $. Mainly, we prove that if $ \mathbf{B} = (B_1, \cdots, B_m) $ is a jointly $ A $-hyponormal $ m $-tuple of commuting operators, then $ \mathbf{B} $ is jointly $ A $-normaloid. This result allows us to establish, for a particular case when $ A $ is the identity operator, a sharp bound for the distance between two jointly hyponormal $ m $-tuples of operators, expressed in terms of the difference between their Taylor spectra. We also aim to introduce and investigate the class of spherically $ A $-$ p $-hyponormal operators with $ 0 < p < 1 $. Additionally, we study the tensor product of specific classes of multivariable operators in semi-Hilbert spaces.</p>

Well-posedness and blow-up results for a time-space fractional diffusion-wave equation

<abstract><p>In this paper, we demonstrate the local well-posedness and blow up of solutions for a class of time- and space-fractional diffusion wave equation in a fractional power space associated with the Laplace operator. First, we give the definition of the solution operator which is a noteworthy extension of the solution operator of the corresponding time-fractional diffusion wave equation. We have analyzed the properties of the solution operator in the fractional power space and Lebesgue space. Next, based on some estimates of the solution operator and source term, we prove the well-posedness of mild solutions by using the contraction mapping principle. We have also investigated the blow up of solutions by using the test function method. The last result describes the properties of mild solutions when $ \alpha\rightarrow1^- $. The main feature of the proof is the reasonable use of continuous embedding between fractional space and Lebesgue space.</p></abstract>

E⋆-local Functions and Ψe⋆ -operator in Ideal Topological Spaces

The main goal of this paper is to introduce another local function to give the possibility of obtaining a Kuratowski closure operator. On the other hand, e⋆-local functions defined for ideal topological spaces have not been found in the current literature. e⋆-local functions for the ideal topological spaces have been described within this work. Moreover, with the help of e⋆-local functions Kuratowski closure operators cl∗e⋆ I and τ ∗e⋆ topology are obtained. Many theorems in the literature have been revised according to the definition of e⋆-local functions

Hilbert–Pólya Operators in Krein Spaces

We construct some class of selfadjoint operators in the Krein spaces consisting of functions onthe straight line \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$ \\{\\operatorname{Re}s=\\frac{1}{2}\\} $\\end{document}.Each of these operators is a rank-one perturbation of a selfadjoint operatorin the corresponding Hilbert spaceand has eigenvalues complex numbers of the form \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$ \\frac{1}{s(1-s)} $\\end{document},where \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$ s $\\end{document} ranges over the set of nontrivial zeros of the Riemann zeta-function.

ON THE CORRECT STATEMENTS OF BOUNDARY VALUE PROBLEMS FOR PDE'S IN BANACH-SOBOLEV SPACES

Abstract. In this report we consider the Banach Functional Space    X , defined on measure space   m ;  , where n R   is bounded domain, m is the Lebesgue measure in n R . It is defined the Banach Sobolev Space    m X W , generated by norm of    X . Regarding these spaces the elliptic equation is considered and the concepts of classical, local, weak and strong solutions are given. One method for defining the trace, trace operator and trace space generated by space    1 X W are introduced. These concepts allow us to consider the boundary value problems for differential equations regarding the spaces    m X W . Finally, it is considered the Dirichlet problem for polyharmonic equations in Sobolev spaces, generated by norm of symmetric spaces and the correct solvability of the corresponding problem is proved.

Real operator spaces and operator algebras

Real operator spaces and operator algebras

Convexity of nonlinear mappings between bounded linear operator spaces

<abstract><p>Motivated by the work <sup>[<xref ref-type="bibr" rid="b7">7</xref>]</sup>, in which the author studied the convexity of nonlinear mappings defined between bounded linear operator spaces, our research extends this inquiry. In this work, we continue the study of the convexity of nonlinear mappings defined between bounded linear operator spaces and we establish a characterization in terms of the second order directional derivative. We apply the main result to prove the convexity and the nonconvexity of well-known nonlinear mappings. The case of nondifferentiable mappings is also treated in the last section.</p></abstract>

Novel bounds for the Euclidean operator radius of Hilbert space operator pairs

Novel bounds for the Euclidean operator radius of Hilbert space operator pairs

Some improvements about numerical radius inequalities for Hilbert space operators

Some improvements about numerical radius inequalities for Hilbert space operators

The positivity of the differential operator generated by hyperbolic system of equations

In the present paper, the initial value problem for the hyperbolic system of equations with nonlocal boundary conditions is investigated. The positivity of the space operator generated by the given problem in interpolation spaces is established. The structure of interpolation spaces of this differential operator is studied. The positivity of this space operator in Slobodeckij-Sobolev spaces is established.

The conjugate operator on variable harmonic Bergman spaces

We prove that the harmonic conjugation operator on variable exponent harmonic Bergman spaces in the unit disc is bounded when the exponent has positive minimum and finite maximum and satisfies the log-Hölder condition. Under these conditions on the exponent, we also give a characterization of variable exponent Bergman spaces in terms of the derivatives of functions in them. Several key lemmas involve the boundedness of various maximal operators in these variable spaces.

Norm and numerical radius inequalities for operator matrices

Operator matrices have played a significant role in studying Hilbert space operators. In this paper, we discuss further properties of operator matrices and present new estimates for the operator norms and numerical radii of such operators. Moreover, operator matrices with positive real and imaginary parts will be discussed, and sharper bounds will be shown for such classes.

On Gradual Borel Summability Method of Rough Convergence of Triple Sequences of Beta Stancu Operators

We define the concept of rough limit set of a triple sequence space of beta Stancu operators of Borel summability of gradual real numbers and obtain the relation between the set of rough limit and the extreme limit points of a triple sequence space of beta Stancu operators of Borel summability method of gradual real numbers. Finally, we investigate some properties of the rough limit set of beta Stancu operators under which Borel summable sequence of gradual real numbers are convergent. Also, we give the results for Borel summability method of series of gradual real numbers.

Algorithmic monotone multiscale finite volume methods for porous media flow

Multiscale finite volume methods are known to produce reduced systems with multipoint stencils which, in turn, could give non-monotone and out-of-bound solutions. We propose a novel solution to the monotonicity issue of multiscale methods. The proposed algorithmic monotone (AM- MsFV/MsRSB) framework is based on an algebraic modification to the original MsFV/MsRSB coarse-scale stencil. The AM-MsFV/MsRSB guarantees monotonic and within bound solutions without compromising accuracy for various coarsening ratios; hence, it effectively addresses the challenge of multiscale methods' sensitivity to coarse grid partitioning choices. Moreover, by preserving the near null space of the original operator, the AM-MsRSB showed promising performance when integrated in iterative formulations using both the control volume and the Galerkin-type restriction operators. We also propose a new approach to enhance the performance of MsRSB for MPFA discretized systems, particularly targeting the construction of the prolongation operator. Results show the potential of our approach in terms of accuracy of the computed basis functions and the overall convergence behavior of the multiscale solver while ensuring a monotone solution at all times.

Time-frequency analysis and coorbit spaces of operators

To analyse the time-frequency content of an ordered data set, it is desirable to consider cross-correlation of time-frequency contents of data points, while maintaining the order of such correlations. To this end, we introduce an operator-valued short-time Fourier transform for certain classes of operators with operator windows, and show that the transform acts in a way analogous to the way the short-time Fourier transform for functions acts, in particular giving rise to a family of vector-valued reproducing kernel Banach spaces, the so-called coorbit spaces, as spaces of operators. As a result of this structure, the operators generating equivalent norms on the function modulation spaces are fully classified. We show that these classes of operators have the same atomic decomposition properties as the function spaces, and use this to give a characterisation of the spaces using localisation operators.

A DIFFERENTIABLE STRUCTURE ON A FINITE DIMENSIONAL REAL VECTOR SPACE AS A MANIFOLD

There are three conditions for a topological space to be said a topological manifold of dimension : Hausdorff space, second-countable, and the existence of homeomorphism of a neighborhood of each point to an open subset of or -dimensional locally Euclidean. The differentiable structure is given if the intersection of two charts is an empty chart or its transition map is differentiable. In this article, we study a differentiable manifold on finite dimensional real vector spaces. The aim is to prove that any finite-dimensional vector space is a differentiable manifold. First of all, it is proved that a finite dimensional vector space is a topological manifold by constructing a norm as its topology. Given a metric which is induced by a norm. Two norms on a finite dimensional vector space are always equivalent and they are determine the same topology. Secondly, it is proved that the transition map in the finite dimensional vector space is differentiable. As conclusion, we have that any finite dimensional vector space with independent norm topology choice is a differentiable manifold. As a matter of discussion, it can be studied that the vector space of all linear operators of a finite dimensional vector space has a differentiable manifold structure as well.

On tensor products with C-normal operators

A bounded linear operator A on H is said to be conjugate normal if CA⁎AC=AA⁎ for some conjugation C on H (in this case, A is said to be C-normal). In this paper, we investigate when the conjugate normality of an operator can be preserved under the operation of tensor product. Given an operator A, we show that the tensor product A⊗B is conjugate normal for any Hilbert space operator B if and only if A2=0. Also we obtain similar results concerning tensor products with skew symmetric operators, g-normal operators and Z-normal operators.

Extension of monotone operators and Lipschitz maps invariant for a group of isometries

Abstract We study monotone operators in reflexive Banach spaces that are invariant with respect to a group of suitable isometric isomorphisms, and we show that they always admit a maximal extension which preserves the same invariance. A similar result applies to Lipschitz maps in Hilbert spaces, thus providing an invariant version of Kirszbraun–Valentine extension theorem. We then provide a relevant application to the case of monotone operators in $L^{p}$ -spaces of random variables which are invariant with respect to measure-preserving isomorphisms, proving that they always admit maximal dissipative extensions which are still invariant by measure-preserving isomorphisms. We also show that such operators are law invariant, a much stronger property which is also inherited by their resolvents, the Moreau–Yosida approximations, and the associated semigroup of contractions. These results combine explicit representation formulae for the maximal extension of a monotone operator based on self-dual Lagrangians and a refined study of measure-preserving maps in standard Borel spaces endowed with a nonatomic measure, with applications to the approximation of arbitrary couplings between measures by sequences of maps.

Raznostnye skhemy dekompozitsii na osnove rasshchepleniya resheniya i operatora zadachi

Domain decomposition methods are used for the approximate solution of boundary value problems for partial differential equations on parallel computing systems. The specifics of nonstationary problems is most completely taken into account when using noniterative domain decomposition schemes. Regionally additive schemes are constructed on the basis of various classes of splitting schemes. A new class of domain decomposition schemes with an additive representation of the solution on a new time level is distinguished that is based on splitting the domain into subdomains based on a partition of unity. An example of the Cauchy problem for first-order evolution equations with a positive self-adjoint operator in a finite-dimensional Hilbert space is considered. Unconditionally stable two- and three-level splitting schemes are constructed for the corresponding system of equations.