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Higher order local dimensions and Baire category

Tom 204 / 2011

Studia Mathematica 204 (2011), 1-20 MSC: Primary 28A80. DOI: 10.4064/sm204-1-1

Streszczenie

Let $X$ be a complete metric space and write $\mathcal{P}(X)$ for the family of all Borel probability measures on $X$. The local dimension $\dim_{\mathsf{loc}}(\mu;x)$ of a measure $\mu\in\mathcal{P}(X)$ at a point $x\in X$ is defined by $$\dim_{\mathsf{loc}}(\mu;x) = \lim_{r\searrow0}\frac{\log\mu(B(x,r))}{\log r}$$ whenever the limit exists, and plays a fundamental role in multifractal analysis. It is known that if a measure $\mu\in\mathcal{P}(X)$ satisfies a few general conditions, then the local dimension of $\mu$ exists and is equal to a constant for $\mu$-a.a. $x\in X$. In view of this, it is natural to expect that for a fixed $x\in X$, the local dimension of a typical (in the sense of Baire category) measure exists at $x$. Quite surprisingly, we prove that this is not the case. In fact, we show that the local dimension of a typical measure fails to exist in a very spectacular way. Namely, the behaviour of a typical measure $\mu\in\mathcal{P}(X)$ is so extremely irregular that, for a fixed $x\in X$, the local dimension function, $$r \mapsto \frac{\log\mu(B(x,r))}{\log r},$$ of $\mu$ at $x$ remains divergent as $r\searrow 0$ even after being “averaged” or “smoothened out” by very general and powerful averaging methods, including, for example, higher order Riesz–Hardy logarithmic averages and Cesàro averages.

Autorzy

• Lars OlsenDepartment of Mathematics
University of St Andrews
St. Andrews, Fife KY16 9SS, Scotland
e-mail

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