measure-preserving
1 Definition
Definition - Let and be measure spaces, and be a measurable transformation. The transformation is said to be measure-preserving if for all we have that
where is, as usual, the set of points such that .
Additional Notation:
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If is bijective, measure-preserving, and its inverse is also measure-preserving, then is said to be an measure-preserving transformation.
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Measure-preserving transformations between the same measure space are sometimes called of the measure space.
Remarks:
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The fact that a map is measure-preserving depends heavily on the sigma-algebras and measures involved. If other measures or sigma-algebras are also in consideration, one should make clear to which measure space is measure-preserving.
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2 Properties
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The composition of measure-preserving maps is again measure-preserving. Of course, we are supposing that the domains and codomains of the maps are such that the composition is possible.
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Let and be measure spaces and and their completions. If is measure-preserving, then so is .
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Let and be measure spaces and , be measure-preserving maps. Then, the product map , defined by
is a measure-preserving transformation of .
3 Examples
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The identity map of a measure space is always measure-preserving.
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Let be a locally compact group (http://planetmath.org/TopologicalGroup). For each , the transformation is measure-preserving relatively to any left Haar measure. Similarly, any right translation on any right Haar measure.
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Every continuous surjective homomorphism between compact Hausdorff is measure-preserving relatively to the normalized Haar measure (see this entry (http://planetmath.org/ContinuousEpimorphismOfCompactGroupsPreservesHaarMeasure)).
Title | measure-preserving |
Canonical name | Measurepreserving |
Date of creation | 2013-03-22 12:19:41 |
Last modified on | 2013-03-22 12:19:41 |
Owner | asteroid (17536) |
Last modified by | asteroid (17536) |
Numerical id | 17 |
Author | asteroid (17536) |
Entry type | Definition |
Classification | msc 28D05 |
Classification | msc 37A05 |
Synonym | measure preserving |
Synonym | measure-preserving transformation |
Synonym | measure-preserving map |
Related topic | ErgodicTransformation |
Defines | invertible measure-preserving transformation |
Defines | endomorphism of a measure space |