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arXiv 1602.03518math.DS
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广义β变换与单峰映射的熵

Generalized beta-transformations and the entropy of unimodal maps

Daniel J. Thompson

摘要:

广义β-变换是一类分段连续区间映射,它是通过取β-变换$x \mapsto βx ~\pmod 1$,其中$β>1$,并将某些分支替换为具有恒定负斜率的分支而得到的。如果1的轨道是有限的,那么映射是马尔可夫的,我们称β(它必须是一个代数数)为广义帕里数。我们表明,这种β的伽罗瓦共轭的模小于2,和模是有界远离2除了例外的情况下,共轭躺在实数线。我们给出了所有这些Galois共轭的闭包的一个特征,并证明了这个集合是路连通的。我们的方法是基于分析的Solomyak的情况下,β-变换。这项工作的一个动机是,一个后临界有限(PCF)单峰映射的熵是一个广义帕里数的对数。因此,我们的结果给出了一个温和的限制,可以通过PCF单峰映射的熵集。

英文摘要:

Generalized beta-transformations are the class of piecewise continuous interval maps given by taking the beta-transformation $x \mapsto βx ~\pmod 1$, where $β>1$, and replacing some of the branches with branches of constant negative slope. If the orbit of 1 is finite, then the map is Markov, and we call beta (which must be an algebraic number) a generalized Parry number. We show that the Galois conjugates of such beta have modulus less than 2, and the modulus is bounded away from 2 apart from the exceptional case of conjugates lying on the real line. We give a characterization of the closure of all these Galois conjugates, and show that this set is path connected. Our approach is based on an analysis of Solomyak for the case of beta-transformations. One motivation for this work is that the entropy of a post-critically finite (PCF) unimodal map is the logarithm of a generalized Parry number. Thus, our results give a mild restriction on the set of entropies that can be attained by PCF unimodal maps.

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