|
|
|
|
|
Measure-preserving Dynamical SystemIn mathematics, a measure-preserving dynamical system is an object of study in the abstract formulation of ergodic theory. It is defined as a probability space and a measure-preserving transformation on it. In more detail, it is a system -
with the following structure: - is a set,
- is a -algebra over ,
- is a probability measure, so that , and
- is a measurable transformation which preserves the measure , i. e. each measurable satisfies
-
-
For example, m could be the normalised angle measure dθ/2π on the unit circle, and T a rotation. One may wonder why the seemingly simpler identity -
is not used. Here is the problem: suppose T : 1 → 1 is defined by T(x) = (4x mod 1), i.e., T(x) is the "fractional part" of 4x. Then the interval 0.02 is mapped to an interval four times as long as itself, but nonetheless the measure of T −1( 0.08 ) = 0.02 ∪ 0.252 ∪ 0.502 ∪ 0.752 is no different from the measure of 0.08. That hypothesis suffices for the proofs of ergodic theorems. This transformation is measure-preserving.
|
 |
|
| Copyright 2005-2009 OnPedia.com. All Rights Reserved |
|
|