Modulo dynamics on [0,1) - MathOverflow most recent 30 from http://mathoverflow.net 2013-05-19T17:48:42Z http://mathoverflow.net/feeds/question/84856 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/84856/modulo-dynamics-on-0-1 Modulo dynamics on [0,1) unknown (google) 2012-01-04T03:38:09Z 2012-01-04T20:42:45Z <p>For <code>$T: \mathbb{R} \mapsto \mathbb{{R}_{+}}$</code>, we have <code>$\{ {T}^{n}(\theta)\ mod \ 1\} \subset [0,1)$</code>. (where <code>${T}^{n}(\theta)$</code> means applying <code>$T$</code> <code>$n$</code> times on <code>$\theta$</code>, not the <code>$n$</code>th power of <code>$T(\theta)$</code>)</p> <p><strong>Question 1:</strong> Does there exist (preferably elementary) <code>$T$</code> such that <code>$\{{T}^{n}(\theta)\ mod \ 1\}$</code> is dense in <code>$[0,1)$</code> for all irrational <code>$\theta \in [0,1)$</code>?</p> <p><strong>Question 2:</strong> Does there exist <code>$T$</code> such that <code>$\{{T}^{n}(\theta)\ mod \ 1\}$</code> is non-periodic (i.e., contains infinite elements) for all <code>$\theta \in [0,1)$</code>?</p> <hr> <p>Edit: @Nikita's comment made me realize that I just asked about a well-known result: See <a href="http://en.wikipedia.org/wiki/Equidistribution_theorem" rel="nofollow" title="Equidistribution theorem">Equidistribution theorem</a>. But this was <strong>NOT</strong> my intention. Weirdly, I somehow just left the irrational rotation behind my mind when considering <code>$T$</code>. So I would still like to know whether the irrational rotation <code>$T(\theta)=\theta+\alpha$</code> is the only class of functions that satisfies question 1 or 2?</p> <p>(I considered <code>$T(\theta)=2\theta$</code>, for example, and they fail both questions. It seems linear growth of <code>$T$</code> and an irrational coefficient are both necessary. Are there functions other than irrational rotation that satisfies question 1 or 2?)</p> http://mathoverflow.net/questions/84856/modulo-dynamics-on-0-1/84891#84891 Answer by Helge for Modulo dynamics on [0,1) Helge 2012-01-04T17:16:54Z 2012-01-04T20:42:45Z <ol> <li><p>Interval Exchange Transformations provide a vast class of further examples. </p></li> <li><p>Let $f:[0,1] \to [0,1]$ be increasing, then the conjugation $f^{-1} \circ T \circ f$ is another example for $T$ being an example. </p></li> <li><p>Let $\mathbb{T} = \mathbb{R}/\mathbb{Z}$. Then for $f:\mathbb{T} \to \mathbb{T}$ twice continuously differentiable with irrational rotation number and transitive, then it is of the previous form. This is known as Denjoy Theorem, Theorem 12.1.1. in Katok, Hasselblatt, Introduction to the modern theory of dynamical systems.</p></li> </ol>