Saturday, October 6, 2018

Distribution of orbits of the doubling map.

Charles had a good remark after the lecture: I told that the orbits of the map x(n+1)=2x(n) mod 1has a uniform distribution on the unit circle, but of course it is easy to see that the point x=0 is a fixed point, so it does not hold for all points (in particular it does not hold for any point with rational initial condition. So let me clarify: my comment holds for almost all initial conditions (a set of initial conditions of full arc length or Lebesgue measure). The exceptional points are dense, but have (as a set) zero length. One can interpret this as saying that if one choses an initial condition randomly, there is zero chance that its orbit does not converge to a uniform distribution.

My comments about this example are only tasters for what is to come later and the explanation of all of the above will be central to the course. 

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