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Circumcenters in real normed spaces

M. S. Tomás (2005)

Bollettino dell'Unione Matematica Italiana

The study of circumcenters in different types of triangles in real normed spaces gives new characterizations of inner product spaces.

Linear maps preserving A -unitary operators

Abdellatif Chahbi, Samir Kabbaj, Ahmed Charifi (2016)

Mathematica Bohemica

Let be a complex Hilbert space, A a positive operator with closed range in ( ) and A ( ) the sub-algebra of ( ) of all A -self-adjoint operators. Assume φ : A ( ) onto itself is a linear continuous map. This paper shows that if φ preserves A -unitary operators such that φ ( I ) = P then ψ defined by ψ ( T ) = P φ ( P T ) is a homomorphism or an anti-homomorphism and ψ ( T ) = ψ ( T ) for all T A ( ) , where P = A + A and A + is the Moore-Penrose inverse of A . A similar result is also true if φ preserves A -quasi-unitary operators in both directions such that there exists an...

n -inner product spaces and projections

Aleksander Misiak, Alicja Ryż (2000)

Mathematica Bohemica

This paper is a continuation of investigations of n -inner product spaces given in [five, six, seven] and an extension of results given in [three] to arbitrary natural n . It concerns families of projections of a given linear space L onto its n -dimensional subspaces and shows that between these families and n -inner products there exist interesting close relations.

On vectorial inner product spaces

João de Deus Marques (2000)

Czechoslovak Mathematical Journal

Let E be a real linear space. A vectorial inner product is a mapping from E × E into a real ordered vector space Y with the properties of a usual inner product. Here we consider Y to be a -regular Yosida space, that is a Dedekind complete Yosida space such that J J = { 0 } , where is the set of all hypermaximal bands in Y . In Theorem 2.1.1 we assert that any -regular Yosida space is Riesz isomorphic to the space B ( A ) of all bounded real-valued mappings on a certain set A . Next we prove Bessel Inequality and Parseval...

Ortogonalidad en espacios normados generalizados.

Rosa Fernández (1988)


Some generalized notions of James' orthogonality and orthogonality in the Pythagorean sense are defined and studied in the case of generalized normed spaces derived from generalized inner products.

Projectively invariant Hilbert-Schmidt kernels and convolution type operators

Jaeseong Heo (2012)

Studia Mathematica

We consider positive definite kernels which are invariant under a multiplier and an action of a semigroup with involution, and construct the associated projective isometric representation on a Hilbert C*-module. We introduce the notion of C*-valued Hilbert-Schmidt kernels associated with two sequences and construct the corresponding reproducing Hilbert C*-module. We also discuss projective invariance of Hilbert-Schmidt kernels. We prove that the range of a convolution type operator associated with...

Two mappings related to semi-inner products and their applications in geometry of normed linear spaces

Sever Silvestru Dragomir, Jaromír J. Koliha (2000)

Applications of Mathematics

In this paper we introduce two mappings associated with the lower and upper semi-inner product ( · , · ) i and ( · , · ) s and with semi-inner products [ · , · ] (in the sense of Lumer) which generate the norm of a real normed linear space, and study properties of monotonicity and boundedness of these mappings. We give a refinement of the Schwarz inequality, applications to the Birkhoff orthogonality, to smoothness of normed linear spaces as well as to the characterization of best approximants.

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