Topological entropy: Difference between revisions

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{{About|a property of dynamical systems|the property of arithmetical semigroups|Abstract analytic number theory}}
In [[mathematics]], '''Smale's axiom A''' defines a class of [[dynamical system]]s which have been extensively studied and whose dynamics is relatively well understood. A prominent example is the [[Smale horseshoe map]]. The term "axiom A" originates with [[Stephen Smale]].<ref>{{citation | first=S. | last=Smale | url=http://www.ams.org/bull/1967-73-06/S0002-9904-1967-11798-1/home.html | title=Differentiable Dynamical Systems | journal=Bull. Amer. Math. Soc. | volume=73 | year=1967 | pages=747–817 | zbl=0202.55202  }}</ref><ref name=R78149>Ruelle (1978) p.149</ref>  The importance of such systems is demonstrated by the [[chaotic hypothesis]], which states that, 'for all practical purposes', that a many-body [[thermostatted system]] is approximated by an [[Anosov system]].<ref>See [http://www.scholarpedia.org/article/Chaotic_hypothesis Scholarpedia, Chaotic hypothesis]</ref>
 
== Definition ==
 
Let ''M'' be a [[smooth manifold]] with a [[diffeomorphism]] ''f'': ''M''→''M''. Then ''f'' is an '''axiom A diffeomorphism''' if
the following two conditions hold:
 
#The [[nonwandering set]] of ''f'', ''&Omega;''(''f''), is a [[hyperbolic set]] and [[Compact space|compact]].
#The set of [[periodic point]]s of ''f'' is [[dense subset|dense]] in ''&Omega;''(''f'').
 
For surfaces, hyperbolicity of the nonwandering set implies the density of periodic points, but this is no longer true in higher dimensions. Nonetheless, axiom A diffeomorphisms are sometimes called '''hyperbolic diffeomorphisms''', because the portion of ''M'' where the interesting dynamics occurs, namely, ''&Omega;''(''f''), exhibits hyperbolic behavior.
 
Axiom A diffeomorphisms generalize [[Morse–Smale system]]s, which satisfy further restrictions (finitely many periodic points and transversality of stable and unstable submanifolds). [[Smale horseshoe map]] is an axiom A diffeomorphism with infinitely many periodic points and positive [[topological entropy]].
 
== Properties ==
 
Any [[Anosov diffeomorphism]] satisfies axiom A. In this case, the whole manifold ''M'' is hyperbolic (although it is an open question whether the non-wandering set ''&Omega;''(''f'') constitutes the whole ''M'').
 
[[Rufus Bowen]] showed that the non-wandering set ''&Omega;''(''f'') of any axiom A diffeomorphism supports a [[Markov partition]].<ref name=R78149/><ref>{{citation | last=Bowen | first=R. | authorlink=Rufus Bowen | title=Markov partitions for axiom A diffeomorphisms | journal=Am. J. Math. | volume=92 | pages=725–747 | year=1970 | zbl=0208.25901 }}</ref>  Thus the restriction of ''f'' to a certain generic subset of ''&Omega;''(''f'') is conjugated to a [[shift of finite type]].
 
The  density of the periodic points in the non-wandering set implies its local maximality: there exists an open neighborhood ''U'' of ''&Omega;''(''f'') such that
 
: <math>\cap_{n\in \mathbb Z} f^{n} (U)=\Omega(f).</math>
 
== Omega stability ==
An important property of Axiom A systems is their structural stability against small perturbations.<ref>Abraham and Marsden, ''Foundations of Mechanics'' (1978) Benjamin/Cummings Publishing, ''see Section 7.5''</ref> That is, trajectories of the perturbed system remain in 1-1 topological correspondence with the unperturbed system. This property is important, in that it shows that Axiom A systems are not exceptional, but are in a sense 'generic'.
 
More precisely, for every ''C''<sup>1</sup>-[[perturbation theory|perturbation]] ''f''<sub>''&epsilon;''</sub> of ''f'', its non-wandering set is formed by two compact, ''f''<sub>''&epsilon;''</sub>-invariant subsets ''&Omega;''<sub>1</sub> and ''&Omega;''<sub>2</sub>. The first subset is homeomorphic to ''&Omega;''(''f'') via a [[homeomorphism]] ''h'' which conjugates the restriction of ''f'' to ''&Omega;''(''f'') with the restriction of ''f''<sub>''&epsilon;''</sub> to ''&Omega;''<sub>1</sub>:
 
: <math>f_\epsilon\circ h(x)=h\circ f(x), \quad \forall x\in \Omega(f).</math>
 
If ''&Omega;''<sub>2</sub> is empty then ''h'' is onto ''&Omega;''(''f''<sub>''&epsilon;''</sub>). If this is the case for every perturbation ''f''<sub>''&epsilon;''</sub> then ''f'' is called '''omega stable'''. A diffeomorphism ''f'' is omega stable if and only if it satisfies axiom A  and the '''no-cycle condition''' (that an orbit, once having left an invariant subset, does not return).
 
== References ==
{{reflist}}
* {{cite book | last=Ruelle | first=David | authorlink=David Ruelle | title=Thermodynamic formalism. The mathematical structures of classical equilibrium | series=Encyclopedia of Mathematics and its Applications | volume=5 | location=Reading, MA | publisher=Addison-Wesley | year=1978 | isbn=0-201-13504-3 | zbl=0401.28016 }}
* {{cite book | last=Ruelle | first=David | authorlink=David Ruelle | title=Chaotic evolution and strange attractors. The statistical analysis of time series for deterministic nonlinear systems | others=Notes prepared by Stefano Isola | series=Lezioni Lincee | publisher=[[Cambridge University Press]] | year=1989 | isbn=0-521-36830-8 | zbl=0683.58001 }}
 
[[Category:Ergodic theory]]
[[Category:Diffeomorphisms]]

Revision as of 15:27, 24 November 2013

29 yr old Orthopaedic Surgeon Grippo from Saint-Paul, spends time with interests including model railways, top property developers in singapore developers in singapore and dolls. Finished a cruise ship experience that included passing by Runic Stones and Church. In mathematics, Smale's axiom A defines a class of dynamical systems which have been extensively studied and whose dynamics is relatively well understood. A prominent example is the Smale horseshoe map. The term "axiom A" originates with Stephen Smale.[1][2] The importance of such systems is demonstrated by the chaotic hypothesis, which states that, 'for all practical purposes', that a many-body thermostatted system is approximated by an Anosov system.[3]

Definition

Let M be a smooth manifold with a diffeomorphism f: MM. Then f is an axiom A diffeomorphism if the following two conditions hold:

  1. The nonwandering set of f, Ω(f), is a hyperbolic set and compact.
  2. The set of periodic points of f is dense in Ω(f).

For surfaces, hyperbolicity of the nonwandering set implies the density of periodic points, but this is no longer true in higher dimensions. Nonetheless, axiom A diffeomorphisms are sometimes called hyperbolic diffeomorphisms, because the portion of M where the interesting dynamics occurs, namely, Ω(f), exhibits hyperbolic behavior.

Axiom A diffeomorphisms generalize Morse–Smale systems, which satisfy further restrictions (finitely many periodic points and transversality of stable and unstable submanifolds). Smale horseshoe map is an axiom A diffeomorphism with infinitely many periodic points and positive topological entropy.

Properties

Any Anosov diffeomorphism satisfies axiom A. In this case, the whole manifold M is hyperbolic (although it is an open question whether the non-wandering set Ω(f) constitutes the whole M).

Rufus Bowen showed that the non-wandering set Ω(f) of any axiom A diffeomorphism supports a Markov partition.[2][4] Thus the restriction of f to a certain generic subset of Ω(f) is conjugated to a shift of finite type.

The density of the periodic points in the non-wandering set implies its local maximality: there exists an open neighborhood U of Ω(f) such that

nfn(U)=Ω(f).

Omega stability

An important property of Axiom A systems is their structural stability against small perturbations.[5] That is, trajectories of the perturbed system remain in 1-1 topological correspondence with the unperturbed system. This property is important, in that it shows that Axiom A systems are not exceptional, but are in a sense 'generic'.

More precisely, for every C1-perturbation fε of f, its non-wandering set is formed by two compact, fε-invariant subsets Ω1 and Ω2. The first subset is homeomorphic to Ω(f) via a homeomorphism h which conjugates the restriction of f to Ω(f) with the restriction of fε to Ω1:

fϵh(x)=hf(x),xΩ(f).

If Ω2 is empty then h is onto Ω(fε). If this is the case for every perturbation fε then f is called omega stable. A diffeomorphism f is omega stable if and only if it satisfies axiom A and the no-cycle condition (that an orbit, once having left an invariant subset, does not return).

References

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  2. 2.0 2.1 Ruelle (1978) p.149
  3. See Scholarpedia, Chaotic hypothesis
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    15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.

    To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010
  5. Abraham and Marsden, Foundations of Mechanics (1978) Benjamin/Cummings Publishing, see Section 7.5