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Erdős measures, sofic measures, and Markov chains
Z. I. Bezhaevaa,
V. I. Oseledetsb a Moscow State Institute of Electronics and Mathematics
b M. V. Lomonosov Moscow State University
Abstract:
We consider random variable
$\zeta=\xi_1\rho+\xi_2\rho^2+\ldots$ where
$\xi_1,\xi_2,\ldots$ are independent identically distibuted random variables taking values 0, 1, with
$P(\xi_i=0)=p_0$,
$P(\xi_i=1)=p_1$,
$0<p_0<1$. Let
$\beta=1/\rho$ be the golden number.
The Fibonacci expansion for a random point
$\rho\zeta$ from
$[0,1]$ is of form
$\eta_1\rho+\eta_2\rho^2+\ldots$ where random variables
$\eta_k=0,1$ and
$\eta_k\eta_{k+1}=0$. The infinite random word
$\eta=\eta_1\eta_2\ldots\eta_n\ldots$ takes values in the Fibonacci compactum and defines an Erdős measure
$\mu(A)=P(\eta\in A)$ on it. The invariant Erdős measure is the shift-invariant measure with
respect to which Erdős measure is absolutely continuous.
We show that Erdős measures are sofic. Recall that a sofic system is a symbolic system which is a continuous factor of a topological Markov chain. A sofic measure is a one-block (or symbol to symbol) factor of the measure corresponding to a homogeneous Markov chain. For Erdős measures the corresponding regular Markov chain has 5 states. This gives ergodic properties of the invariant Erdős measure.
We give a new ergodic theory proof of the singularity of the distribution of the random variable
$\zeta$.
Our method is also applicable when
$\xi_1,\xi_2,\ldots$ is a stationary Markov chain taking values 0, 1.
In particular, we prove that the distribution of
$\zeta$ is singular and that Erdős measures appear as result of gluing together states in a regular Markov chain with 7 states.
UDC:
519.217,
517.518.1 Received: 08.04.2005