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Boundary-value problems for two-dimensional canonical systems

- S. Hassi, H. Snoo, H. Winkler
- Mathematics
- 1 December 2000

The two-dimensional canonical systemJy′=−ℓHy where the nonnegative Hamiltonian matrix functionH(x) is trace-normed on (0, ∞) has been studied in a function-theoretic way by L. de Branges in [5]–[8].… Expand

Boundary relations and their Weyl families

- V. Derkach, S. Hassi, M. Malamud, H. Snoo
- Mathematics
- 1 December 2006

The concepts of boundary relations and the corresponding Weyl families are introduced. Let S be a closed symmetric linear operator or, more generally, a closed symmetric relation in a Hilbert space… Expand

Lebesgue type decompositions for nonnegative forms

- S. Hassi, Z. Sebestyén, H. Snoo
- Mathematics
- 15 December 2009

Self-Adjoint Extensions of Symmetric Subspaces

- A. Dijksma, H. Snoo
- Mathematics
- 1 September 1974

A theory of self-adjoint extensions of closed symmetric linear manifolds beyond the original space is presented. It is based on the Cayley transform of linear manifolds. Resolvent and spectral… Expand

Boundary relations and generalized resolvents of symmetric operators

- V. Derkach, S. Hassi, M. Malamud, H. Snoo
- Mathematics
- 9 October 2006

The Kreĭn-Naĭmark formula provides a parametrization of all selfadjoint exit space extensions of a (not necessarily densely defined) symmetric operator in terms of maximal dissipative (in ℂ+)… Expand

A general factorization approach to the extension theory of nonnegative operators and relations

- S. Hassi, A. Sandovici, H. Snoo, H. Winkler
- Mathematics
- 2007

The Krein-von Neumann and the Friedrichs extensions of a nonnegative linear operator or relation (i.e., a multivalued operator) are characterized in terms of factorizations. These factorizations lead… Expand

Unitary colligations in Krein spaces and their role in the extension theory of isometries and symmetric linear relations in Hilbert spaces

- A. Dijksma, H. Langer, H. Snoo
- Mathematics
- 1987

Let H be a Hilbert space and let S be a closed linear relation in H, i.e., S is a * subspace of H 2 such that ScS*cH 2 (for the definition of S and other definitions see Section I). Furthermore, let… Expand

Boundary Relations, Unitary Colligations, and Functional Models

- J. Behrndt, S. Hassi, H. Snoo
- Mathematics
- 1 March 2009

Abstract.Recently a new notion, the so-called boundary relation, has been introduced involving an analytic object, the so-called Weyl family. Weyl families and boundary relations establish a link… Expand

The structure of linear relations in Euclidean spaces

- A. Sandovici, H. Snoo, H. Winkler
- Mathematics
- 1 March 2005

On the class of extremal extensions of a nonnegative operator

- Y. Arlinskii̇̆, S. Hassi, Z. Sebestyén, H. Snoo
- Mathematics
- 2001

A nonnegative selfadjoint extension Aof a nonnegative operator A is called extremal if inf {(A)(ϕ) - f),ϕ - f) : ∈ dom A} = 0 for all ϕ ∈ dom A.A new construction of all extremal extensions of a… Expand

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