Convexity, boundedness, and almost periodicity for differential equations in Hilbert space.
Correction to "Approximation with Restricted Spectra".
Cyclic space isomorphism of unitary operators
We introduce a new equivalence relation between unitary operators on separable Hilbert spaces and discuss a possibility to have in each equivalence class a measure-preserving transformation.
Diagonality in C*-Algebras.
Diagonalization of a self-adjoint operator acting on a Hilbert module.
Diagonals of Self-adjoint Operators with Finite Spectrum
Given a finite set X⊆ ℝ we characterize the diagonals of self-adjoint operators with spectrum X. Our result extends the Schur-Horn theorem from a finite-dimensional setting to an infinite-dimensional Hilbert space analogous to Kadison's theorem for orthogonal projections (2002) and the second author's result for operators with three-point spectrum (2013).
Domaine Numérique du produit AB avec A normal
2000 Mathematics Subject Classification: 18B30, 47A12.Let A, B be two linear operators on a complex Hilbert space H. We extend a Bouldin's result (1969) conserning W(AB) - the numerical range of the product AB. We show, when AB = BA and A is normal, than W(AB).
Existence of the smallest selfadjoint extension
Exponentials of bounded normal operators
The present paper is mainly concerned with equations involving exponentials of bounded normal operators. Conditions implying commutativity of normal operators are given, without using the known 2πi-congruence-free hypothesis. This is a continuation of a recent work by the second author.
Factorization of -quasihyponormal operators.
Factorization Of Quasihyponormal Operators
Factorization of quasihyponormal operators.
Finite-rank perturbations of positive operators and isometries
We completely characterize the ranks of A - B and for operators A and B on a Hilbert space satisfying A ≥ B ≥ 0. Namely, let l and m be nonnegative integers or infinity. Then l = rank(A - B) and for some operators A and B with A ≥ B ≥ 0 on a Hilbert space of dimension n (1 ≤ n ≤ ∞) if and only if l = m = 0 or 0 < l ≤ m ≤ n. In particular, this answers in the negative the question posed by C. Benhida whether for positive operators A and B the finiteness of rank(A - B) implies that of . For...
Functional Analysis, Orthogonal Polynomials And A Theorem Of Markov.
Functions of operators and their commutators in perturbation theory
This paper shows some directions of perturbation theory for Lipschitz functions of selfadjoint and normal operators, without giving precise proofs. Some of the ideas discussed are explained informally or for the finite-dimensional case. Several unsolved problems are mentioned.
Generalization of Weyl-von Neumann-Berg theorem for the case of normal operator-valued holomorphic functions
Geometry of oblique projections
Let A be a unital C*-algebra. Denote by P the space of selfadjoint projections of A. We study the relationship between P and the spaces of projections determined by the different involutions induced by positive invertible elements a ∈ A. The maps sending p to the unique with the same range as p and sending q to the unitary part of the polar decomposition of the symmetry 2q-1 are shown to be diffeomorphisms. We characterize the pairs of idempotents q,r ∈ A with ||q-r|| < 1 such that...
Hidden symmetry from supersymmetry in one-dimensional quantum mechanics.
Homogeneous operators
Integral transforms of vector measures on semigroups with applications to spectral operators.