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  • Articles  (9)
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  • 47B35  (9)
  • Springer  (9)
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  • 1995-1999  (9)
  • 1985-1989
  • 1999  (9)
  • Mathematics  (9)
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  • Articles  (9)
  • Other Sources
Publisher
  • Springer  (9)
  • Taylor & Francis
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  • 1995-1999  (9)
  • 1985-1989
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  • Mathematics  (9)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The journal of Fourier analysis and applications 5 (1999), S. 21-44 
    ISSN: 1531-5851
    Keywords: 42B99 ; 47B35 ; 15A54 ; 60G35 ; Positive extensions ; Toeplitz operators ; matrix functions on bitorus ; Wiener algebra ; band method ; entropy ; almost periodic functions ; ARMA processes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Let S be a band in Z2 bordered by two parallel lines that are of equal distance to the origin. Given a positive definite ℓ1 sequence of matrices {cj}j∈S we prove that there is a positive definite matrix function f in the Wiener algebra on the bitorus such that the Fourier coefficients $$\widehat{f(k)}$$ equal ck for k ∈ S. A parameterization is obtained for the set of all positive extensions f of {cj}j∈S. We also prove that among all matrix functions with these properties, there exists a distinguished one that maximizes the entropy. A formula is given for this distinguished matrix function. The results are interpreted in the context of spectral estimation of ARMA processes.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The journal of Fourier analysis and applications 5 (1999), S. 599-615 
    ISSN: 1531-5851
    Keywords: 41A25 ; 42C15 ; 47B35 ; 15A99 ; shift-invariant systems ; finite section method ; block Toeplitz matrices ; Laurent operator ; Gabor frame ; filter banks ; band matrices
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A shift-invariant system is a collection of functions {gm,n} of the form gm,n(k)=gm(k−an). Such systems play an important role in time-frequency analysis and digital signal processing. A principal problem is to find a dual system γm,n(k)=γm(k−an) such that each functionf can be written asf= ∑〈f, γm,n〉gm,n. The mathematical theory usually addresses this problem in infinite dimensions (typically in L2 (ℝ) or ℓ2(ℤ)), whereas numerical methods have to operate with a finite-dimensional model. Exploiting the link between the frame operator and Laurent operators with matrix-valued symbol, we apply the finite section method to show that the dual functions obtained by solving a finite-dimensional problem converge to the dual functions of the original infinite-dimensional problem in ℓ2(ℤ). For compactly supported gm, n (FIR filter banks) we prove an exponential rate of convergence and derive explicit expressions for the involved constants. Further we investigate under which conditions one can replace the discrete model of the finite section method by the periodic discrete model, which is used in many numerical procedures. Again we provide explicit estimates for the speed of convergence. Some remarks on tight frames complete the paper.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Integral equations and operator theory 34 (1999), S. 227-233 
    ISSN: 1420-8989
    Keywords: 47B35
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In the paper, we give characterizations of Hankel operators on generalizedH 2 spaces and obtain some properties for corresponding Hankel algebras.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Integral equations and operator theory 34 (1999), S. 500-501 
    ISSN: 1420-8989
    Keywords: 47B35 ; 32M15
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Integral equations and operator theory 35 (1999), S. 118-121 
    ISSN: 1420-8989
    Keywords: 46L05 ; 47B35
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Integral equations and operator theory 33 (1999), S. 273-304 
    ISSN: 1420-8989
    Keywords: 47D ; 47G ; 47B20 ; 46A67 ; 46L45 ; 47A53 ; 47B35 ; 46L87 ; 19K33 ; 19D55
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We give a new2 index theorem for the basic example of Toeplitz operators on the circle. The joint torsion, a non zero complex valued analytic index, of a pair of Fredholm Toeplitz operatorsT ϕ andT ψ withH ∞ symbols is computed by residues in the disk, and is determined by a monodromy integral which specifies the isomorphism class of ϕυψ a flat line bundle on the circle. When the symbols ϕ and ψ are rational a product of joint torsions identifies the isomorphism class of the bundle inH 1 (S 1,C *), and the identification extends by rational approximation to the case of smooth symbols defined on the circle.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Integral equations and operator theory 33 (1999), S. 426-455 
    ISSN: 1420-8989
    Keywords: 47B35 ; 32M15
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Let Ω be an irreducible bounded symmetric domain of genusp, h(x, y) its Jordan triple determinant, andA ν 2 (Ω) the standard weighted Bergman space of holomorphic functions on Ω square-integrable with respect to the measureh(z, z) ν−p dz. Extending the recent result of Axler and Zheng for Ω=D, ν=p=2 (the unweighted Bergman space on the unit disc), we show that ifS is a finite sum of finite products of Toeplitz operators onA ν 2 (Ω) and ν is sufficiently large, thenS is compact if and only if the Berezin transform $$\bar S$$ ofS tends to zero asz approaches ∂Ω. An analogous assertion for the Fock space is also obtained.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Integral equations and operator theory 34 (1999), S. 107-126 
    ISSN: 1420-8989
    Keywords: 47B35 ; 47D25
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Let $$\mathbb{D}$$ be the unit disk inℂ, $$\mathcal{A}^2 (\mathbb{D})$$ be the Bergman space, consisting of all analytic functions from $$L_2 (\mathbb{D})$$ , and $$B_\mathbb{D} $$ be the Bergman projection of $$L_2 (\mathbb{D})$$ onto $$\mathcal{A}^2 (\mathbb{D})$$ . We constructC *-algebras $$\mathcal{A} \subset L_\infty (\mathbb{D})$$ , for functions of which the commutator of Toeplitz operators [T a ,T b ]=T a T b −T b T a is compact, and, at the same time, the semi-commutator [T a ,T b )=T a T b −T ab is not compact. It is proved, that for each finite set ∧=〈n 0,n 1, ...,n m 〉, where 1=n 0 〈n 1 〈...〈n m ≤∞, andn k ∈ℕ∪ {∞}, there are algebras $$\mathcal{A}_\Lambda $$ of the above type, such that the symbol algebras Sym $$\mathcal{T}(\mathcal{A}_\Lambda )$$ of Toeplitz operator algebras $$\mathcal{T}(\mathcal{A}_\Lambda )$$ arecommutative, while the symbol algebras Sym $$\mathcal{R}(\mathcal{A}_\Lambda ,B_\mathbb{D} )$$ of the algebras $$\mathcal{R}(\mathcal{A}_\Lambda ,B_\mathbb{D} )$$ , generated by multiplication operators $$a \in \mathcal{A}_\Lambda $$ and $$B_\mathbb{D} $$ , haveirreducible representations exactly of dimensions n 0,n 1,..., n m .
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Integral equations and operator theory 35 (1999), S. 271-365 
    ISSN: 1420-8989
    Keywords: 47D ; 47G ; 47B20 ; 46A67 ; 46L45 ; 47A53 ; 47B35 ; 46L87 ; 19K33 ; 19D55
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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