scholarly journals Conjugations in $$L^2$$ and their invariants

2020 ◽  
Vol 10 (2) ◽  
Author(s):  
M. Cristina Câmara ◽  
Kamila Kliś–Garlicka ◽  
Bartosz Łanucha ◽  
Marek Ptak
Keyword(s):  
Hardy Space ◽  
Unit Circle ◽  
Unilateral Shift ◽  
Model Spaces

Abstract Conjugations in space $$L^2$$ L 2 of the unit circle commuting with multiplication by z or intertwining multiplications by z and $${{\bar{z}}}$$ z ¯ are characterized. We also study their behaviour with respect to the Hardy space, subspaces invariant for the unilateral shift and model spaces.

scholarly journals Hyponormal Toeplitz operators on H2(T) with polynomial symbols

1996 ◽  
Vol 144 ◽  
pp. 179-182 ◽  
Author(s):  
Dahai Yu
Keyword(s):  
Functional Equation ◽  
Hardy Space ◽  
Closed Form ◽  
Unit Circle ◽  
Toeplitz Operator ◽  
Explicit Expression ◽  
Complex Plane ◽  
Toeplitz Operators ◽  
Computing Process

Let T be the unit circle on the complex plane, H2(T) be the usual Hardy space on T, Tø be the Toeplitz operator with symbol Cowen showed that if f1 and f2 are functions in H such that is in Lø, then Tf is hyponormal if and only if for some constant c and some function g in H∞ with Using it, T. Nakazi and K. Takahashi showed that the symbol of hyponormal Toeplitz operator Tø satisfies and and they described the ø solving the functional equation above. Both of their conditions are hard to check, T. Nakazi and K. Takahashi remarked that even “the question about polynomials is still open” [2]. Kehe Zhu gave a computing process by way of Schur’s functions so that we can determine any given polynomial ø such that Tø is hyponormal [3]. Since no closed-form for the general Schur’s function is known, it is still valuable to find an explicit expression for the condition of a polynomial á such that Tø is hyponormal and depends only on the coefficients of ø, here we have one, it is elementary and relatively easy to check. We begin with the most general case and the following Lemma is essential.

scholarly journals Model spaces and Toeplitz kernels in reflexive Hardy space

2016 ◽  
pp. 127-148 ◽  
Author(s):  
M. C. Câmara ◽  
M. T. Malheiro ◽  
Jonathan R. Partington
Keyword(s):  
Hardy Space ◽  
Model Spaces

scholarly journals The compression of a slant Hankel operator to H2

2003 ◽  
Vol 74 (88) ◽  
pp. 129-136
Author(s):  
Taddesse Zegeye ◽  
S.C. Arora
Keyword(s):  
Unit Circle ◽  
Complex Plane ◽  
Hankel Operator ◽  
Inner Product ◽  
Unilateral Shift

A slant Hankel operator K? with symbol ? in L?(T) (in short L?), where T is the unit circle on the complex plane, is an operator whose representing matrix M = (aij) is given by ai,j = (?,z-2i-j), where (?, ?) is the usual inner product in L2(T) (in short L2). The operator L? denotes the compression of K? to H2(T) (in short H2). We prove that an operator L on H2 is the compression of a slant Hankel operator to H2 if and only if U *L = LU2, where U is the unilateral shift. Moreover, we show that a hyponormal L? is necessarily normal and L? can not be an isometry.

Hardy space decomposition of on the unit circle:

2016 ◽  
Vol 61 (4) ◽  
pp. 510-523 ◽  
Author(s):  
Hai-Chou Li ◽  
Guan-Tie Deng ◽  
Tao Qian
Keyword(s):  
Hardy Space ◽  
Unit Circle ◽  
Space Decomposition

The maximal operator of the Marcinkiewicz-Fejér means of the 2-dimensional Vilenkin-Fourier series

2008 ◽  
Vol 45 (3) ◽  
pp. 321-331
Author(s):  
István Blahota ◽  
Ushangi Goginava
Keyword(s):  
Fourier Series ◽  
Hardy Space ◽  
Maximal Operator ◽  
Fejér Means

In this paper we prove that the maximal operator of the Marcinkiewicz-Fejér means of the 2-dimensional Vilenkin-Fourier series is not bounded from the Hardy space H2/3 ( G2 ) to the space L2/3 ( G2 ).

The Restricted Arc-Width of a Graph

10.37236/1734 ◽  
2003 ◽  
Vol 10 (1) ◽  
Author(s):  
David Arthur
Keyword(s):  
Unit Circle ◽  
Single Point ◽  
Minimum Width ◽  
Graph Operations ◽  
Function Mapping

An arc-representation of a graph is a function mapping each vertex in the graph to an arc on the unit circle in such a way that adjacent vertices are mapped to intersecting arcs. The width of such a representation is the maximum number of arcs passing through a single point. The arc-width of a graph is defined to be the minimum width over all of its arc-representations. We extend the work of Barát and Hajnal on this subject and develop a generalization we call restricted arc-width. Our main results revolve around using this to bound arc-width from below and to examine the effect of several graph operations on arc-width. In particular, we completely describe the effect of disjoint unions and wedge sums while providing tight bounds on the effect of cones.

The range of block Hankel operators

Filomat ◽  
2018 ◽  
Vol 32 (9) ◽  
pp. 3237-3243
Author(s):  
In Hwang ◽  
In Kim ◽  
Sumin Kim
Keyword(s):  
Hardy Space ◽  
Invariant Subspace ◽  
Hankel Operators ◽  
Coprime Factorization ◽  
Backward Shift ◽  
Vector Valued

In this note we give a connection between the closure of the range of block Hankel operators acting on the vector-valued Hardy space H2Cn and the left coprime factorization of its symbol. Given a subset F ? H2Cn, we also consider the smallest invariant subspace S*F of the backward shift S* that contains F.

scholarly journals Multi-orbital Frames Through Model Spaces

2021 ◽  
Vol 15 (1) ◽  
Author(s):  
Carlos Cabrelli ◽  
Ursula Molter ◽  
Daniel Suárez
Keyword(s):  
Model Spaces
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