Behaviour of solutions of a fourth-order self-adjoint linear differential equation
Marko Švec (1983)
Annales Polonici Mathematici
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Marko Švec (1983)
Annales Polonici Mathematici
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Masakazu Naito, Sohtaro Doro, Daisuke Minematsu, Ryohei Miyadera (2009)
Visual Mathematics
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J. van Casteren, Seymour Goldberg (1970)
Studia Mathematica
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Heydar Radjavi, Ping-Kwan Tam, Kok-Keong Tan (2003)
Studia Mathematica
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A characterization of compactness of a given self-adjoint bounded operator A on a separable infinite-dimensional Hilbert space is established in terms of the spectrum of perturbations. An example is presented to show that without separability, the perturbation condition, which is always necessary, is not sufficient. For non-separable spaces, another condition on the self-adjoint operator A, which is necessary and sufficient for the perturbation, is given.
Konrad Schmüdgen (1986)
Manuscripta mathematica
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Mohammed Hichem Mortad (2011)
Colloquium Mathematicae
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We present a new approach to the question of when the commutativity of operator exponentials implies that of the operators. This is proved in the setting of bounded normal operators on a complex Hilbert space. The proofs are based on some results on similarities by Berberian and Embry as well as the celebrated Fuglede theorem.
Leopold Herrmann (1988)
Aplikace matematiky
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The operator , , , is shown to be essentially self-adjoint, positive definite with a compact resolvent. The conditions on (in fact, on a general symmetric operator) are given so as to justify the application of the Fourier method for solving the problems of the types and , respectively.
Bent Fuglede (1982)
Mathematica Scandinavica
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Jocić, Danko R. (1997)
Matematichki Vesnik
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Salah Mecheri (2015)
Colloquium Mathematicae
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Let A ∈ B(H) and B ∈ B(K). We say that A and B satisfy the Fuglede-Putnam theorem if AX = XB for some X ∈ B(K,H) implies A*X = XB*. Patel et al. (2006) showed that the Fuglede-Putnam theorem holds for class A(s,t) operators with s + t < 1 and they mentioned that the case s = t = 1 is still an open problem. In the present article we give a partial positive answer to this problem. We show that if A ∈ B(H) is a class A operator with reducing kernel and B* ∈ B(K) is a class 𝓨 operator,...
Santtu Ruotsalainen (2012)
Studia Mathematica
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Antilinear operators on a complex Hilbert space arise in various contexts in mathematical physics. In this paper, an analogue of the Weyl-von Neumann theorem for antilinear self-adjoint operators is proved, i.e. that an antilinear self-adjoint operator is the sum of a diagonalizable operator and of a compact operator with arbitrarily small Schatten p-norm. On the way, we discuss conjugations and their properties. A spectral integral representation for antilinear self-adjoint operators...