• Publications
• Influence
Boundary-value problems for two-dimensional canonical systems
• 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].
Boundary relations and their Weyl families
• 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
Boundary relations and generalized resolvents of symmetric operators
• 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+)
A general factorization approach to the extension theory of nonnegative operators and relations
• 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
Square‐integrable solutions and Weyl functions for singular canonical systems
• Mathematics
• 1 August 2011
Boundary value problems for singular canonical systems of differential equations of the form \documentclass{article}\usepackage{amssymb}\begin{document}\pagestyle{empty}  Jf^{\prime }(t)-H(t)
A canonical decomposition for linear operators and linear relations
• Mathematics
• 2 November 2006
An arbitrary linear relation (multivalued operator) acting from one Hilbert space to another Hilbert space is shown to be the sum of a closable operator and a singular relation whose closure is the
Boundary Relations, Unitary Colligations, and Functional Models
• 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
On the class of extremal extensions of a nonnegative operator
• 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