Approximation of Derivatives of Analytic Functions from One Hardy Class by Another Hardy Class

On the Hermite expansions of functions from Hardy class by

Considering functions f on Rn for which both f and f̂ are bounded by the Gaussian e 1 2 a|x| , 0 < a < 1 we show that their Fourier-Hermite coefficients have exponential decay. Optimal decay is obtained for O(n)−finite functions thus extending the one dimensional result of Vemuri [11].

Hardy space of operator-valued analytic functions

We are concerned with Hardy and BMO spaces of operator-valued functions analytic in the unit disk of C. In the case of the Hardy space, we involve the atomic decomposition since the usual argument in the scalar setting is not suitable. Several properties (the Garsia-norm equivalent theorem, Carleson measure, and so on) of BMOA spaces are extended to the operator-valued setting. Then, the operat...

On the applications of Hardy class functions in scattering theory

This paper is a response to an article [26] recently published in Journal of Physics A: Mathematical and Theoretical. The article claims that the theory of resonances and decaying states based on certain rigged Hilbert spaces of Hardy functions is physically untenable. In this paper we show that all of the key conclusions of [26] are the result of either the errors in mathematical reasoning or ...

Classification Theory for Hardy Classes of Analytic Functions

Constrained Hardy space approximation

We consider the problem of minimizing the distance ‖f − φ‖Lp(K), where K is a subset of the complex unit circle ∂D and φ ∈ C(K), subject to the constraint that f lies in the Hardy space H(D) and |f | ≤ g for some positive function g. This problem occurs in the context of filter design for causal LTI systems. We show that the optimization problem has a unique solution, which satisfies an extrema...