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600833 
Journal Article 
HILBERT-SCHMIDT OPERATORS AND FRAMES — CLASSIFICATION, BEST APPROXIMATION BY MULTIPLIERS AND ALGORITHMS 
Balazs, P 
2008 
6 
2 
315-330 
In this paper we deal with the theory of Hilbert–Schmidt operators, when the usual choice of orthonormal basis, on the associated Hilbert spaces, is replaced by frames. We More precisely, we provide a necessary and sufficient condition for an operator to be Hilbert–Schmidt, based on its action on the elements of a frame (i.e. an operator T is $\mathcal{H}S$ if and only if the sum of the squared norms of T applied on the elements of the frame is finite). Also, we construct Bessel sequences, frames and Riesz bases of $\mathcal{H}S$ operators using tensor products of the same sequences in the associated Hilbert spaces. We state how the $\mathcal{H}S$ inner product of an arbitrary operator and a rank one operator can be calculated in an efficient way; and we use this result to provide a numerically efficient algorithm to find the best approximation, in the Hilbert–Schmidt sense, of an arbitrary matrix, by a so-called frame multiplier (i.e. an operator which act diagonally on the frame analysis coefficients). Finally, we give some simple examples using Gabor and wavelet frames, introducing in this way wavelet multipliers. [ABSTRACT FROM AUTHOR] Copyright of International Journal of Wavelets, Multiresolution & Information Processing is the property of World Scientific Publishing Company and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts) 
HILBERT algebras; HILBERT schemes; FRAMES (Vector analysis); MULTIPLIERS (Mathematical analysis); ALGORITHMS; best approximation by operators; frame multiplier; Frames; Gabor multiplier; Hilbert–Schmidt operators; Hilbert-Schmidt operators; wavelet multiplier