Displaying similar documents to “Minimization of constrained quadratic forms in Hilbert spaces.”

Distances between composition operators.

Valentin Matache (2007)

Extracta Mathematicae

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Composition operators C induced by a selfmap φ of some set S are operators acting on a space consisting of functions on S by composition to the right with φ, that is Cf = f º φ. In this paper, we consider the Hilbert Hardy space H on the open unit disk and find exact formulas for distances ||C - C|| between composition operators. The selfmaps φ and ψ involved in those formulas are constant, inner, or analytic selfmaps of the unit disk fixing the origin.

Singular quadratic functionals of one dependent variable

Zuzana Došlá, Ondřej Došlý (1995)

Commentationes Mathematicae Universitatis Carolinae

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Singular quadratic functionals of one dependent variable with nonseparated boundary conditions are investigated. Necessary and sufficient conditions for nonnegativity of these functionals are derived using the concept of and . The paper also includes two comparison theorems for coupled points with respect to the various boundary conditions.

Quadratic functionals with a variable singular end point

Zuzana Došlá, PierLuigi Zezza (1992)

Commentationes Mathematicae Universitatis Carolinae

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In this paper we introduce the definition of coupled point with respect to a (scalar) quadratic functional on a noncompact interval. In terms of coupled points we prove necessary (and sufficient) conditions for the nonnegativity of these functionals.