Churchill–Bernstein equation: Difference between revisions

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In [[mathematics]] &mdash; specifically, in [[measure theory]] &mdash; '''Malliavin's absolute continuity lemma''' is a result due to the [[France|French]] [[mathematician]] [[Paul Malliavin]] that plays a foundational rôle in the regularity ([[smooth function|smoothness]]) [[theorem]]s of the [[Malliavin calculus]].  Malliavin's lemma gives a sufficient condition for a [[finite measure|finite]] [[Borel measure]] to be [[absolute continuity|absolutely continuous]] with respect to [[Lebesgue measure]].
 
==Statement of the lemma==
 
Let ''&mu;'' be a finite Borel measure on ''n''-[[dimension]]al [[Euclidean space]] '''R'''<sup>''n''</sup>. Suppose that, for every ''x''&nbsp;&isin;&nbsp;'''R'''<sup>''n''</sup>, there exists a constant ''C''&nbsp;=&nbsp;''C''(''x'') such that
 
:<math>\left| \int_{\mathbf{R}^{n}} \mathrm{D} \varphi (y) (x) \, \mathrm{d} \mu(y) \right| \leq C(x) \| \varphi \|_{\infty}</math>
 
for every ''C''<sup>&infin;</sup> function ''φ''&nbsp;:&nbsp;'''R'''<sup>''n''</sup>&nbsp;&rarr;&nbsp;'''R''' with [[compact support]].  Then ''μ'' is absolutely continuous with respect to ''n''-dimensional Lebesgue measure ''λ''<sup>''n''</sup> on '''R'''<sup>''n''</sup>.  In the above, D''φ''(''y'') denotes the [[Fréchet derivative]] of ''&phi;'' at ''y'' and ||''φ''||<sub>&infin;</sub> denotes the [[supremum norm]] of ''φ''.
 
==References==
 
* {{cite book
| last = Bell
| first = Denis R.
| title = The Malliavin calculus
| publisher = Dover Publications Inc.
| location = Mineola, NY
| year = 2006
| pages = x+113
| isbn = 0-486-44994-7
}} {{MathSciNet|id=2250060}} (See section 1.3)
* {{cite book
| last = Malliavin
| first = Paul
| authorlink = Paul Malliavin
| chapter = Stochastic calculus of variations and hypoelliptic operators
| title = Proceedings of the International Symposium on Stochastic Differential Equations (Res. Inst. Math. Sci., Kyoto Univ., Kyoto, 1976)
| pages= 195–263
| publisher = Wiley
| location = New York
| year = 1978
}} {{MathSciNet|id=536013}}
 
[[Category:Lemmas]]
[[Category:Measure theory]]

Revision as of 13:47, 12 January 2014

In mathematics — specifically, in measure theoryMalliavin's absolute continuity lemma is a result due to the French mathematician Paul Malliavin that plays a foundational rôle in the regularity (smoothness) theorems of the Malliavin calculus. Malliavin's lemma gives a sufficient condition for a finite Borel measure to be absolutely continuous with respect to Lebesgue measure.

Statement of the lemma

Let μ be a finite Borel measure on n-dimensional Euclidean space Rn. Suppose that, for every x ∈ Rn, there exists a constant C = C(x) such that

|RnDφ(y)(x)dμ(y)|C(x)φ

for every C function φ : Rn → R with compact support. Then μ is absolutely continuous with respect to n-dimensional Lebesgue measure λn on Rn. In the above, Dφ(y) denotes the Fréchet derivative of φ at y and ||φ|| denotes the supremum norm of φ.

References