A note on nth roots of positive operators

1969 ◽  
Vol 66 (1) ◽  
pp. 27-30
Author(s):  
John H. Jowett
Keyword(s):  
Hilbert Space ◽  
Existence And Uniqueness ◽  
Spectral Representation ◽  
Bounded Operator ◽  
Positive Operators

The existence and uniqueness of a positive self-adjoint nth. root of a positive, self-adjoint, not necessarily bounded operator on a Hilbert Space H can be readily demonstrated using the spectral representation of the transformation.

scholarly journals Correctness conditions for high-order differential equations with unbounded coefficients

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Kordan N. Ospanov
Keyword(s):  
Differential Equation ◽  
Hilbert Space ◽  
Existence And Uniqueness ◽  
Sufficient Conditions ◽  
Integral Operators ◽  
Order Linear Differential Equation ◽  
Unbounded Coefficients ◽  
Weighted Norms ◽  
Uniqueness Of The Solution ◽  
Linear Differential

AbstractWe give some sufficient conditions for the existence and uniqueness of the solution of a higher-order linear differential equation with unbounded coefficients in the Hilbert space. We obtain some estimates for the weighted norms of the solution and its derivatives. Using these estimates, we show the conditions for the compactness of some integral operators associated with the resolvent.

scholarly journals Application of Localization to the Multivariate Moment Problem

2014 ◽  
Vol 115 (2) ◽  
pp. 269 ◽  
Author(s):  
Murray Marshall
Keyword(s):  
Hilbert Space ◽  
Moment Problem ◽  
Existence And Uniqueness ◽  
Positive Semidefinite ◽  
Linear Functionals ◽  
Localization Technique ◽  
Adjoint Operators

It is explained how the localization technique introduced by the author in [19] leads to a useful reformulation of the multivariate moment problem in terms of extension of positive semidefinite linear functionals to positive semidefinite linear functionals on the localization of $\mathsf{R}[\underline{x}]$ at $p = \prod_{i=1}^n(1+x_i^2)$ or $p' = \prod_{i=1}^{n-1}(1+x_i^2)$. It is explained how this reformulation can be exploited to prove new results concerning existence and uniqueness of the measure $\mu$ and density of $\mathsf{C}[\underline{x}]$ in $\mathscr{L}^s(\mu)$ and, at the same time, to give new proofs of old results of Fuglede [11], Nussbaum [21], Petersen [22] and Schmüdgen [27], results which were proved previously using the theory of strongly commuting self-adjoint operators on Hilbert space.

scholarly journals A non-linear hyperbolic equation

1980 ◽  
Vol 3 (3) ◽  
pp. 505-520 ◽  
Author(s):  
Eliana Henriques de Brito
Keyword(s):  
Hilbert Space ◽  
Cauchy Problem ◽  
Weak Solution ◽  
Real Number ◽  
Hyperbolic Equation ◽  
Existence And Uniqueness ◽  
Linear Hyperbolic Equation ◽  
Non Linear

In this paper the following Cauchy problem, in a Hilbert spaceH, is considered:(I+λA)u″+A2u+[α+M(|A12u|2)]Au=fu(0)=u0u′(0)=u1Mandfare given functions,Aan operator inH, satisfying convenient hypothesis,λ≥0andαis a real number.Foru0in the domain ofAandu1in the domain ofA12, ifλ>0, andu1inH, whenλ=0, a theorem of existence and uniqueness of weak solution is proved.

scholarly journals A NOTE ON VARIATIONAL SOLUTIONS TO SPDE PERTURBED BY GAUSSIAN NOISE IN A GENERAL CLASS

2009 ◽  
Vol 12 (02) ◽  
pp. 353-358
Author(s):  
MICHAEL RÖCKNER ◽  
YI WANG
Keyword(s):  
Hilbert Space ◽  
Gaussian Noise ◽  
Stochastic Partial Differential Equations ◽  
General Class ◽  
Existence And Uniqueness ◽  
Nonlinear Operators ◽  
Infinite Dimensional ◽  
Variational Solutions ◽  
Cylindrical Wiener Process ◽  
Monotonicity Conditions

This note deals with existence and uniqueness of (variational) solutions to the following type of stochastic partial differential equations on a Hilbert space [Formula: see text][Formula: see text] where A and B are random nonlinear operators satisfying monotonicity conditions and G is an infinite dimensional Gaussian process adapted to the same filtration as the cylindrical Wiener process W(t),t ≥ 0.

A SIMILARITY BETWEEN THE GROSS LAPLACIAN AND THE LÉVY LAPLACIAN

2007 ◽  
Vol 10 (02) ◽  
pp. 261-276 ◽  
Author(s):  
UN CIG JI ◽  
KIMIAKI SAITÔ
Keyword(s):  
Stochastic Process ◽  
Hilbert Space ◽  
Hilbert Spaces ◽  
Existence And Uniqueness ◽  
Infinitesimal Generator ◽  
Separable Hilbert Space ◽  
Fock Spaces ◽  
Parameter Group ◽  
Infinite Dimensional ◽  
Lévy Laplacian

In this paper we present a construction of an infinite dimensional separable Hilbert space associated with a norm induced from the Lévy trace. The space is slightly different from the Cesàro Hilbert space introduced in Ref. 1. The Lévy Laplacian is discussed with a suitable domain which is constructed by a rigging of Fock spaces based on a rigging of Hilbert spaces with the Lévy trace. Then the Lévy Laplacian can be considered as the Gross Laplacian acting on a certain countable Hilbert space. By constructing one-parameter group of operators of which the infinitesimal generator is the Lévy Laplacian, we study the existence and uniqueness of solution of heat equation associated with the Lévy Laplacian. Moreover we give an infinite dimensional stochastic process generated by the Lévy Laplacian.

scholarly journals An operator inequality

1984 ◽  
Vol 7 (1) ◽  
pp. 205-207
Author(s):  
P. D. Siafarikas
Keyword(s):  
Hilbert Space ◽  
Separable Hilbert Space ◽  
Positive Operators ◽  
Operator Inequality

An inequality is proved in abstract separable Hilbert spaceHwhereAandBare bounded self-adjoint positive operators defined inHsuch thatR(A)=R(B)andR(A)is closed.

scholarly journals Hilbert space structure and positive operators

2005 ◽  
Vol 305 (2) ◽  
pp. 560-565 ◽  
Author(s):  
Dimosthenis Drivaliaris ◽  
Nikos Yannakakis
Keyword(s):  
Hilbert Space ◽  
Space Structure ◽  
Positive Operators
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