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Dynamical systems on measure spaces, invariant measures, ergodic averages, mixing properties.

9 votes

Quantitative versions of ergodic theorem

For the specific case you mention of an irrational rotation of the circle, it depends on the rotation number $r$. You can get slow asymptotic convergence for something like $$r=\sum{10^{-n!}}$$ (and y …
Martin M. W.'s user avatar
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3 votes
Accepted

Are $C^1$ vector fields generating an ergodic flow $C^0$ dense?

You can't always approximate by ergodic flows, because ergodic flows might not even exist. For example, on $S^2$ the Poincare-Bendixson theorem rules out ergodic flows, but there are many measure-pres …
Martin M. W.'s user avatar
  • 6,571
5 votes
Accepted

The Arnold cat map

Unless I'm misinterpreting the question, the SRB measure is just Lebesgue measure... the cat map is hyperbolic, preserves area, and is topologically transitive. See Theorem 3.10 and the following rema …
Martin M. W.'s user avatar
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9 votes
Accepted

A regularity property of transition matrices for the cat map

The reason that the matrices are alike is that, up to a multiplicative factor, each is approximately encoding $Area(T(R_i) \cap R_j))$. This is because the rational points with denominator $q$ are clo …
Martin M. W.'s user avatar
  • 6,571
3 votes

Existence of a continuous ergodic dynamical system for a given distribution?

Let $\mu$ be Lebesgue measure on $S^1$, and $\delta_P$ be a point-mass at a point $P \in S^1$. Then there is no flow on $S^1$ whose time averages lead to $\frac{1}{2}(\mu + \delta_P)$. (Consider the o …
Martin M. W.'s user avatar
  • 6,571
4 votes
Accepted

Is there a similar theorem in the partially hyperbolic case?

I think this runs into trouble at condition 1. For example, let $f : M \to M$ be an Anosov diffeomorphism that satisfies these conditions. The map $g: M \times S^1 \to M \times S^1$ defined by $g = f …
Martin M. W.'s user avatar
  • 6,571