Geometric means of quasi-Toeplitz matrices

被引:0
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作者
Dario A. Bini
Bruno Iannazzo
Jie Meng
机构
[1] Università di Pisa,Dipartimento di Matematica
[2] Università degli Studi di Perugia,Dipartimento di Matematica e Informatica
[3] Ocean University of China,School of Mathematical Sciences
来源
BIT Numerical Mathematics | 2023年 / 63卷
关键词
Quasi-Toeplitz matrices; Toeplitz algebra; Matrix functions; Operator mean; Geometric mean; Continuous functional calculus; 15A48; 15B05; 47A64; 47B35; 47A60; 65F30;
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摘要
We study means of geometric type of quasi-Toeplitz matrices, that are semi-infinite matrices A=(ai,j)i,j=1,2,…\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$A=(a_{i,j})_{i,j=1,2,\ldots }$$\end{document} of the form A=T(a)+E\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$A=T(a)+E$$\end{document}, where E represents a compact operator, and T(a) is a semi-infinite Toeplitz matrix associated with the function a, with Fourier series ∑k=-∞∞akeikt\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sum _{k=-\infty }^{\infty } a_k e^{{{\mathfrak {i}}}k t}$$\end{document}, in the sense that (T(a))i,j=aj-i\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(T(a))_{i,j}=a_{j-i}$$\end{document}. If a is real valued and essentially bounded, then these matrices represent bounded self-adjoint operators on ℓ2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\ell ^2$$\end{document}. We prove that if a1,…,ap\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$a_1,\ldots ,a_p$$\end{document} are continuous and positive functions, or are in the Wiener algebra with some further conditions, then matrix geometric means, such as the ALM, the NBMP and the weighted mean of quasi-Toeplitz positive definite matrices associated with a1,…,ap\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$a_1,\ldots ,a_p$$\end{document}, are quasi-Toeplitz matrices associated with the function (a1⋯ap)1p\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(a_1\cdots a_p)^{\frac{1}{p}}$$\end{document}, which differ only by the compact correction. We introduce numerical algorithms for their computation and show by numerical tests that these operator means can be effectively approximated numerically.
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