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Displaying 5221 – 5240 of 11160

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Nonexpansive retractions in Hilbert spaces

Kazimierz Goebel, Ewa Sędłak (2009)

Annales UMCS, Mathematica

Let H be a Hilbert space and C ⊂ H be closed and convex. The mapping P: H → C known as the nearest point projection is nonexpansive (1-lipschitzian). We observed that, the natural question: "Are there nonexpansive projections Q: H → C other than P?" is neglected in the literature. Also, the answer is not often present in the "folklore" of the Hilbert space theory. We provide here the answer and discuss some facts connected with the subject.

Nonexpansive retracts in Banach spaces

Eva Kopecká, Simeon Reich (2007)

Banach Center Publications

We study various aspects of nonexpansive retracts and retractions in certain Banach and metric spaces, with special emphasis on the compact nonexpansive envelope property.

Nonhermitian systems and pseudospectra

Lloyd N. Trefethen (2005/2006)

Séminaire Équations aux dérivées partielles

Four applications are outlined of pseudospectra of highly nonnormal linear operators.

Non-holomorphic functional calculus for commuting operators with real spectrum

Mats Andersson, Bo Berndtsson (2002)

Annali della Scuola Normale Superiore di Pisa - Classe di Scienze

We consider n -tuples of commuting operators a = a 1 , ... , a n on a Banach space with real spectra. The holomorphic functional calculus for a is extended to algebras of ultra-differentiable functions on n , depending on the growth of exp ( i a · t ) , t n , when | t | . In the non-quasi-analytic case we use the usual Fourier transform, whereas for the quasi-analytic case we introduce a variant of the FBI transform, adapted to ultradifferentiable classes.

Non-hyperreflexive reflexive spaces of operators

Roman V. Bessonov, Janko Bračič, Michal Zajac (2011)

Studia Mathematica

We study operators whose commutant is reflexive but not hyperreflexive. We construct a C₀ contraction and a Jordan block operator S B associated with a Blaschke product B which have the above mentioned property. A sufficient condition for hyperreflexivity of S B is given. Some other results related to hyperreflexivity of spaces of operators that could be interesting in themselves are proved.

Noninvertibility preservers on Banach algebras

Bojan Kuzma (2006)

Czechoslovak Mathematical Journal

It is proved that a linear surjection Φ 𝒜 , which preserves noninvertibility between semisimple, unital, complex Banach algebras, is automatically injective.

Nonlinear analysis. New arguments and results.

Lamberto Cesari (1984)

Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni

Si presentano condizioni sufficienti in forma astratta per l'esistenza di soluzioni di equazioni operazionali non lineari la cui parte lineare non è autoaggiunta.

Nonlinear analysis. New arguments and results. II.

Lamberto Cesari (1984)

Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni

We continue here the discussion in part I, and we state and prove further sufficient conditions for the existence of a solution to nonselfadjoint problems.

Nonlinear boundary value problems for second order differential inclusions

Sophia Th. Kyritsi, Nikolaos M. Matzakos, Nikolaos S. Papageorgiou (2005)

Czechoslovak Mathematical Journal

In this paper we study two boundary value problems for second order strongly nonlinear differential inclusions involving a maximal monotone term. The first is a vector problem with Dirichlet boundary conditions and a nonlinear differential operator of the form x a ( x , x ' ) ' . In this problem the maximal monotone term is required to be defined everywhere in the state space N . The second problem is a scalar problem with periodic boundary conditions and a differential operator of the form x ( a ( x ) x ' ) ' . In this case the maximal...

Nonlinear contractive conditions: A comparison and related problems

Jacek Jachymski, Izabela Jóźwik (2007)

Banach Center Publications

We establish five theorems giving lists of nonlinear contractive conditions which turn out to be mutually equivalent. We derive them from some general lemmas concerning subsets of the plane which may be applied both in the single- or set-valued case as well as for a family of mappings. A separation theorem for concave functions is proved as an auxiliary result. Also, we discuss briefly the following problems for several classes of contractions: stability of procedure of successive approximations,...

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