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In mathematics, Fatou components are components of the Fatou set. They were named after Pierre Fatou.

• Rational case

• Attracting periodic point

• Herman ring

• More than one type of component

• Transcendental case

• Baker domain

• Wandering domain

• See also

• References

• Bibliography

If f is a rational function

f = P ( z ) Q ( z ) {\displaystyle f={\frac {P(z)}{Q(z)}}}

defined in the extended complex plane, and if it is a nonlinear function (degree > 1)

d ( f ) = max ( deg ⁡ ⁡ ( P ) , deg ⁡ ⁡ ( Q ) ) ≥ ≥ 2 , {\displaystyle d(f)=\max(\deg(P),\,\deg(Q))\geq 2,}

then for a periodic component U {\displaystyle U} of the Fatou set, exactly one of the following holds:

1. U {\displaystyle U} contains an attracting periodic point

2. U {\displaystyle U} is paraboliccite-ref-1[1]

3. U {\displaystyle U} is a Siegel disc: a simply connected Fatou component on which f(z) is analytically conjugate to a Euclidean rotation of the unit disc onto itself by an irrational rotation angle.

4. U {\displaystyle U} is a Herman ring: a double connected Fatou component (an annulus) on which f(z) is analytically conjugate to a Euclidean rotation of a round annulus, again by an irrational rotation angle.

The components of the map f ( z ) = z − − ( z 3 − − 1 ) / 3 z 2 {\displaystyle f(z)=z-(z^{3}-1)/3z^{2}} contain the attracting points that are the solutions to z 3 = 1 {\displaystyle z^{3}=1} . This is because the map is the one to use for finding solutions to the equation z 3 = 1 {\displaystyle z^{3}=1} by Newton–Raphson formula. The solutions must naturally be attracting fixed points.

The map

f ( z ) = e 2 π π i t z 2 ( z − − 4 ) / ( 1 − − 4 z ) {\displaystyle f(z)=e^{2\pi it}z^{2}(z-4)/(1-4z)}

and t = 0.6151732... will produce a Herman ring.cite-ref-2[2] It is shown by Shishikura that the degree of such map must be at least 3, as in this example.

If degree d is greater than 2 then there is more than one critical point and then can be more than one type of component

In case of transcendental functions there is another type of periodic Fatou components, called Baker domain: these are "domains on which the iterates tend to an essential singularity (not possible for polynomials and rational functions)"cite-ref-3[3]cite-ref-4[4] one example of such a function is:cite-ref-5[5] f ( z ) = z − − 1 + ( 1 − − 2 z ) e z {\displaystyle f(z)=z-1+(1-2z)e^{z}}

Transcendental maps may have wandering domains: these are Fatou components that are not eventually periodic.

• No-wandering-domain theorem

• Montel's theorem

• John Domainscite-ref-6[6]

• Basins of attraction

cite-note-11. ↑ wikibooks : parabolic Julia sets

cite-note-22. ↑ citerefmilnor1990Milnor, John W. (1990), Dynamics in one complex variable, arXiv:math/9201272, Bibcode:1992math......1272M

cite-note-33. ↑ An Introduction to Holomorphic Dynamics (with particular focus on transcendental functions)by L. Rempe

cite-note-44. ↑ Siegel Discs in Complex Dynamics by Tarakanta Nayak

cite-note-55. ↑ A transcendental family with Baker domains by Aimo Hinkkanen, Hartje Kriete and Bernd Krauskopf

cite-note-66. ↑ JULIA AND JOHN REVISITED by NICOLAE MIHALACHE

• Lennart Carleson and Theodore W. Gamelin, Complex Dynamics, Springer 1993.

• Alan F. Beardon Iteration of Rational Functions, Springer 1991.