## 2011.38: The Hausdorff dimension of some random invariant graphs

2011.38:
A Moss and C. P. Walkden
(2011)
*The Hausdorff dimension of some random
invariant graphs.*

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## Abstract

Weierstrass’ example of an everywhere continuous but nowhere differentiable function is given by w(x) = P1 n=0 n cos 2bnx where 2 (0, 1), b 2, b > 1. There is a well-known and widely accepted, but as yet unproven, formula for the Hausdorff dimension of the graph of w. Hunt [H] proved that this formula holds almost surely on the addition of a random phase shift. The graphs of Weierstrass-type functions appear as repellers for a certain class of dynamical system; in this note we prove formulae analogous to those for random phase shifts of w(x) but in a dynamic context. Let T : S1 ! S1 be a uniformly expanding map of the circle. Let : S1 ! (0, 1), p : S1 ! R and define the function w(x) = P1 n=0 (x)(T(x)) · · · (Tn−1(x))p(Tn(x)). The graph of w is a repelling invariant set for the skew-product transformation T(x, y) = (T(x), (x)−1(y−p(x))) on S1×R and is continuous but typically nowhere differentiable. With the addition of a random phase shift in p, and under suitable hypotheses including a partial hyperbolicity assumption on the skew-product, we prove an almost sure formula for the Hausdorff dimension of the graph of w using a generalisation of techniques from [H] coupled with thermodynamic formalism.

Item Type: | MIMS Preprint |
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Subjects: | MSC 2000 > 37 Dynamical systems and ergodic theory |

MIMS number: | 2011.38 |

Deposited By: | Ms Lucy van Russelt |

Deposited On: | 14 May 2011 |

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