Výsledky vyhledávání - "Heinz Langer"

W. Stenger's and M.A. Nudelman's results and resolvent formulas involving compressions

Autor: Heinz Langer, Aad Dijksma

Publikováno v: Advances in operator theory, 5(3), 936-949. SPRINGER BASEL AG

In the first part of this note we give a rather short proof of a generalization of Stenger’s lemma about the compression $$A_0$$ to $${{\mathfrak {H}}}_0$$ of a self-adjoint operator A in some Hilbert space $${{\mathfrak {H}}}={{\mathfrak {H}}}_0\o

Externí odkaz: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::0a6e4f73211bfed4ca55be2f8b2b599c
https://research.rug.nl/en/publications/fe69d15f-660a-42f6-8f7e-71c764676be9

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Self-Adjoint Extensions of a Symmetric Linear Relation with Finite Defect: Compressions and Straus Subspaces

Autor: Heinz Langer, Aad Dijksma

Publikováno v: Complex Function Theory, Operator Theory, Schur Analysis and Systems Theory ISBN: 9783030448189

Let S be a symmetric relation with finite and equal defect numbers in the Hilbert space $\mathfrak H$. If $\widetilde A$ is a self-adjoint extension of S in some larger Hilbert space $\widetilde {\mathfrak H}$, the compression of \(\widetilde A

Externí odkaz: https://explore.openaire.eu/search/publication?articleId=doi_________::13ae4bc8cfe58f9c87328321e428884e
https://doi.org/10.1007/978-3-030-44819-6_10

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Rational eigenvalue problems and applications to photonic crystals

Autor: Christian Engström, Christiane Tretter, Heinz Langer

Publikováno v: Journal of Mathematical Analysis and Applications. 445:240-279

We establish new analytic results for a general class of rational spectral problems. They arise e.g. in modelling photonic crystals whose capability to control the flow of light depends on specific ...

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https://doi.org/10.1016/j.jmaa.2016.07.048

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Compressed resolvents and reduction of spectral problems on star graphs

Autor: B. Malcolm Brown, Christiane Tretter, Heinz Langer

Publikováno v: Brown, B. Malcolm; Langer, Heinz; Tretter, Christiane (2019). Compressed resolvents and reduction of spectral problems on star graphs. Complex analysis and operator theory, 13(1), pp. 291-320. Birkhäuser 10.1007/s11785-018-0793-6

In this paper a two-step reduction method for spectral problems on a star graph with n+1 edges e_{0}, e_{1}, \ldots , e_{n} and a self-adjoint matching condition at the central vertex v is established. The first step is a reduction to the problem on

Externí odkaz: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::3f52c6294e2e09569d05beee20fb97a2
https://boris.unibe.ch/132259/1/10.1007_s11785-018-0793-6.pdf

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Maximal J-semi-definite invariant subspaces of unbounded J-selfadjoint operators in Krein spaces

Autor: Heinz Langer, Christiane Tretter

Publikováno v: Journal of Mathematical Analysis and Applications. 494:124597

In this paper we establish conditions for the existence of maximal J -semi-definite invariant subspaces of unbounded J -selfadjoint operators. Our results allow for operators where all entries of the formal matrix representation induced by the indefi

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https://doi.org/10.1016/j.jmaa.2020.124597

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Compressions of Self-Adjoint Extensions of a Symmetric Operator and M.G. Krein’s Resolvent Formula

Autor: Heinz Langer, Aad Dijksma

Publikováno v: Integral equations and operator theory, 90(4):41. SPRINGER BASEL AG

Let S be a symmetric operator with finite and equal defect numbers in the Hilbert space $${{\mathfrak {H}}}$$ . We study the compressions $$P_{{\mathfrak {H}}}\widetilde{A}\big |_{{\mathfrak {H}}}$$ of the self-adjoint extensions $$\widetilde{A}$$ of

Externí odkaz: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::30de96de4cc5916ef0e91714351765b5
https://doi.org/10.1007/s00020-018-2465-3

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Spectral Theory of the Klein-Gordon Equation in Krein Spaces

Autor: Christiane Tretter, Branko Najman, Heinz Langer

Publikováno v: Langer, Heinz; Najman, Branko; Tretter, Christiane (2008). Spectral theory of the Klein-Gordon equation in Krein spaces. Proceedings of the Edinburgh Mathematical Society, 51(3), pp. 711-750. Cambridge: Cambridge University Press 10.1017/S0013091506000150

In this paper the spectral properties of the abstract Klein–Gordon equation are studied. The main tool is an indefinite inner product known as the charge inner product. Under certain assumptions on the potential V, two operators are associated with

Externí odkaz: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::a527655f770841a98fad8d6d3f50c2f4
http://doc.rero.ch/record/290540/files/S0013091506000150.pdf

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Finite-dimensional self-adjoint extensions of a symmetric operator with finite defect and their compressions

Autor: Aad Dijksma, Heinz Langer

Publikováno v: Advances in Complex Analysis and Operator Theory, 135-163
STARTPAGE=135;ENDPAGE=163;TITLE=Advances in Complex Analysis and Operator Theory
Trends in Mathematics ISBN: 9783319623610

Let S be a symmetric operator with finite and equal defect numbers d in the Hilbert space $\mathfrak{H}$, and with a boundary triplet $(\mathbb{C}^d, \Gamma_1, \Gamma_2)$. Following the method of E.A. Coddington, we describe all self-adjoint exte

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https://research.rug.nl/en/publications/a8667ac6-0a52-4048-bc2b-40080d33b0bf

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Continuation of Hermitian Positive Definite Functions and Related Questions

Autor: Heinz Langer, Mark G. Krein

Publikováno v: Integral Equations and Operator Theory. 78:1-69

We study the intimate relation of the continuation problem for hermitian positive definite functions with direct and inverse spectral problems for canonical systems and strings and with the extrapolation problem for second order stochastic processes.

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https://doi.org/10.1007/s00020-013-2091-z

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Bessel-Type Operators with an Inner Singularity

Autor: B. Malcolm Brown, Matthias Langer, Heinz Langer

Publikováno v: Integral Equations and Operator Theory. 75:257-300

We consider a Bessel-type differential expression on [0, a], a > 1, with the singularity at the inner point x = 1, see (1.2) below. This singularity is in the limit point case from both sides. Therefore in a Hilbert space treatment in L2(0, a), e.g.

Externí odkaz: https://explore.openaire.eu/search/publication?articleId=doi_________::25c68c5f93841562a3cabdeba77c90a7
https://doi.org/10.1007/s00020-012-2023-3

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