# Ultrametric subsets with large Hausdorff dimension

Manor Mendel, Assaf Naor

Abstract:It is shown that for every $\e\in (0,1)$, every compact metric space $(X,d)$ has a compact subset $S\subseteq X$ that embeds into an ultrametric space with distortion $O(1/\e)$, and $$\dim_H(S)\ge (1-\e)\dim_H(X),$$ where $\dim_H(\cdot)$ denotes Hausdorff dimension. The above $O(1/\e)$ distortion estimate is shown to be sharp via a construction based on sequences of expander graphs.
Random models
0
0
Entering edit mode
8 months ago
Omar ▴ 30

In the construction of the expander fractals was there anything special about using the Erdos-Renyi model for random graphs or could you have done the same or similar construction using other random models for graphs?

Expanders • 130 views