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Difference between revisions of "Entropy of a measurable decomposition"

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''<img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/e/e035/e035750/e0357501.png" /> of a space with a normalized measure <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/e/e035/e035750/e0357502.png" />''
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''$\xi$ of a space with a normalized measure $(X,\mu)$''
  
A concept defined as follows. If the elements of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/e/e035/e035750/e0357503.png" /> having measure zero form in total a set of positive measure, then the entropy of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/e/e035/e035750/e0357504.png" /> is <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/e/e035/e035750/e0357505.png" />; otherwise
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A concept defined as follows. If the elements of $\xi$ having measure zero form in total a set of positive measure, then the entropy of $\xi$ is $H(\xi)=\infty$; otherwise
  
<table class="eq" style="width:100%;"> <tr><td valign="top" style="width:94%;text-align:center;"><img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/e/e035/e035750/e0357506.png" /></td> </tr></table>
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$$H(\xi)=-\sum\mu(C)\log\mu(C),$$
  
where the sum is taken over all elements of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/e/e035/e035750/e0357507.png" /> of positive measure. The logarithm is usually to the base 2.
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where the sum is taken over all elements of $\xi$ of positive measure. The logarithm is usually to the base 2.
  
  

Latest revision as of 08:36, 29 August 2014

$\xi$ of a space with a normalized measure $(X,\mu)$

A concept defined as follows. If the elements of $\xi$ having measure zero form in total a set of positive measure, then the entropy of $\xi$ is $H(\xi)=\infty$; otherwise

$$H(\xi)=-\sum\mu(C)\log\mu(C),$$

where the sum is taken over all elements of $\xi$ of positive measure. The logarithm is usually to the base 2.


Comments

Instead of "measurable decomposition" the phrase "measurable partitionmeasurable partition" is often used, cf. [a1].

References

[a1] I.P. [I.P. Kornfel'd] Cornfel'd, S.V. Fomin, Ya.G. Sinai, "Ergodic theory" , Springer (1982) (Translated from Russian)
How to Cite This Entry:
Entropy of a measurable decomposition. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Entropy_of_a_measurable_decomposition&oldid=12139
This article was adapted from an original article by D.V. Anosov (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article