Let T be an operator-weighted shift whose weights are 2-by-2 matrices. We say that, given > 0, T is in the -canonical form if each weight is an upper triangular matrix (aij), with 0 ≤ a11, a22 ≤ 1 and a12 6= 0 implies a11, a22 < . We generalize this concept to operator-weighted shifts whose weights are n-by-n matrices and we show that every polynomially bounded weighted shift, whose weights are...

The main aim of this paper is to prove that the maximal operator σ∗ of the Fejér means of the two dimensional character system of the p-series field in the Kaczmarz rearrangement is bounded from the Hardy space Hα to the space Lα for α > 1/2, provided that the supremum in the maximal operator is taken over a positive cone. We also prove that the maximal operator σ∗ 0 of Fejér means of the two d...

Abstract. The dynamical systems method (DSM) is justified for solving operator equations F (u) = f , where F is a nonlinear operator in a Hilbert space H. It is assumed that F is a global homeomorphism of H onto H, that F ∈ C loc, that is, it has the Fréchet derivative F ′(u) continuous with respect to u, that the operator [F ′(u)]−1 exists for all u ∈ H and is bounded, ||[F ′(u)]−1|| ≤ m(u), w...

Abstract. Let T and V be two Hilbert space contractions and let X be a linear bounded operator. It was proved by C. Foias and J.P. Williams that in certain cases the operator block matrix R(X ;T, V ) (equation (1.1) below) is similar to a contraction if and only if the commutator equation X = TZ−ZV has a bounded solution Z. We characterize here the similarity to contractions of some operator ma...

In this paper, we study frames for bounded linear operators and defined the notion of Ad-operator frame for Banach spaces. A necessary and sufficient condition for a sequence of bounded linear operators to be an Ad-operator frame has been given. Some characterizations of Ad-operator frames have been discussed. Further, a method has been given to generate a -Banach frame using a Schauder frame. ...

A bounded linear operator T on a complex Hilbert space H is called complex symmetric if T = CT ∗C, where C is a conjugation (an isometric, antilinear involution of H). We prove that T = CJ |T |, where J is an auxiliary conjugation commuting with |T | = √ T ∗T . We consider numerous examples, including the Poincaré-Neumann singular integral (bounded) operator and the Jordan model operator (compr...

If m is a positive integer, let ǫk = e 2kπi/m for k = 1, . . . ,m. Then ǫk = 1 (k = 1, . . . ,m), ǫk 6= 1 (k = 1, . . . ,m− 1) and ǫm = 1 . If a ∈ A is invertible, define the bounded linear operator Ta : A → A by Tax = a xa (x ∈ A) . Proposition 1. Suppose that a ∈ A is invertible, m is a positive integer and that σ(a) is irrotational (mod 2π/m). Let the bounded linear operator S : A → A be giv...

We consider the function class E generated by the constant functions, the projection functions, the predecessor function, the substitution operator, and the recursion on notation operator. Furthermore, we introduce regressive machines, i.e. register machines which have the division by 2 and the predecessor as basic operations. We show that E is the class of functions computable by regressive ma...

The norm of a bounded composition operator induced by a disc automorphism is estimated on weighted Hardy spaces H(β) in which the classical Hardy space is continuously embedded. The estimate obtained is accurate in the sense that it provides the exact norm for particular instances of the sequence β. As a by-product of our results, an estimate for the norm of any bounded composition operator on ...

We study operators with located graph in Bishop-style constructive mathematics. It is shown that a bounded operator has an adjoint if and only if its graph is located. Locatedness of the graph is a necessary and sufficient condition for an unbounded normal operator to have a spectral decomposition. These results suggest that located operators are the right generalization of bounded operators wi...