对称基和贪婪基的等距理论中的反例

IF 0.9 3区 数学 Q2 MATHEMATICS
Fernando Albiac , José L. Ansorena , Óscar Blasco , Hùng Việt Chu , Timur Oikhberg
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引用次数: 0

摘要

我们继续在Albiac和Wojtaszczyk(2006)中开始的研究,在涉及的常数尖锐的情况下,即在它们等于1的情况下与贪婪基有关的性质。我们在这里的主要目标是提供一个Banach空间的例子,该空间的基满足性质(a),但不是1-抑制无条件的,从而解决了Albiac和Ansorena(2017)的问题4.4。特别地,我们的构造证明了具有性质(A)的基不必是1-贪婪的,即使附加了它们是无条件和对称的假设。我们还展示了这个例子的有限维对应,并表明,至少在有限维设置中,性质(a)不会传递给对偶。作为我们论点的副产品,我们证明了对称基是无条件的当且仅当它是全的,从而推广了对称Schauder基是无限制的众所周知的结果。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Counterexamples in isometric theory of symmetric and greedy bases

We continue the study initiated in Albiac and Wojtaszczyk (2006) of properties related to greedy bases in the case when the constants involved are sharp, i.e., in the case when they are equal to 1. Our main goal here is to provide an example of a Banach space with a basis that satisfies Property (A) but fails to be 1-suppression unconditional, thus settling Problem 4.4 from Albiac and Ansorena (2017). In particular, our construction demonstrates that bases with Property (A) need not be 1-greedy even with the additional assumption that they are unconditional and symmetric. We also exhibit a finite-dimensional counterpart of this example, and show that, at least in the finite-dimensional setting, Property (A) does not pass to the dual. As a by-product of our arguments, we prove that a symmetric basis is unconditional if and only if it is total, thus generalizing the well-known result that symmetric Schauder bases are unconditional.

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来源期刊
CiteScore
1.90
自引率
11.10%
发文量
55
审稿时长
6-12 weeks
期刊介绍: The Journal of Approximation Theory is devoted to advances in pure and applied approximation theory and related areas. These areas include, among others: • Classical approximation • Abstract approximation • Constructive approximation • Degree of approximation • Fourier expansions • Interpolation of operators • General orthogonal systems • Interpolation and quadratures • Multivariate approximation • Orthogonal polynomials • Padé approximation • Rational approximation • Spline functions of one and several variables • Approximation by radial basis functions in Euclidean spaces, on spheres, and on more general manifolds • Special functions with strong connections to classical harmonic analysis, orthogonal polynomial, and approximation theory (as opposed to combinatorics, number theory, representation theory, generating functions, formal theory, and so forth) • Approximation theoretic aspects of real or complex function theory, function theory, difference or differential equations, function spaces, or harmonic analysis • Wavelet Theory and its applications in signal and image processing, and in differential equations with special emphasis on connections between wavelet theory and elements of approximation theory (such as approximation orders, Besov and Sobolev spaces, and so forth) • Gabor (Weyl-Heisenberg) expansions and sampling theory.
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