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Revision as of 00:26, 18 May 2011 by imported>Dmitrii Kouznetsov ({{Image_Details|user-pd |description = Iterations of the logistic transfer function $f(x)=4x(1\!-\!x)$ (shown qith thick black line) $y=f^c(x)$ for $c=$ 0.2, 0.5, 0.8, 1, 1,5 . Function $f$ is iterated $c$ times; however, the number $c$ of iterations has no need to be integer. This pic was generated with the "universal" algorithm that evaluates the iterations of more general function $f_u(x)=u~x~ (1\!-\!x)$; see <ref name="logistic"> http://www.springerlink.com/content/u712vtp4122544x...)
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Summary

Title / Description


Iterations of the logistic transfer function $f(x)=4x(1\!-\!x)$ (shown qith thick black line) $y=f^c(x)$ for $c=$ 0.2, 0.5, 0.8, 1, 1,5 . Function $f$ is iterated $c$ times; however, the number $c$ of iterations has no need to be integer. This pic was generated with the "universal" algorithm that evaluates the iterations of more general function $f_u(x)=u~x~ (1\!-\!x)$; see [1]. Namely for $u\!=\!4$, the iterates can be expressed through the elementary function, and such a plot can be generated, for example, in Mathematica with very simple code: F[c_, z_] = 1/2 (1 - Cos[2^c ArcCos[1 - 2 z]]) Plot[{F[1.5, x], F[1, x], F[.8, x], F[.5, x], F[.2, x]}, {x, 0, 1}] In order to keep the code short, the colors are not adjusted. The representation above can be obtained from the representation of the superfunction $F$ and the Abel function $G$: : $f^c(z)=F(c+G(z))$ at : $F(z)= \frac{1}{2}(1−\cos(2z))$ : $G(z)=F^{-1}(z)=\log_2(\arccos(1\!−\!2z))$
Citizendium author


Dmitrii Kouznetsov
Date created


March 2011
Country of first publication


Japan
Notes


More superfunctions represented through elementary functions can be found in

[2].

Copyleft 2011 by Dmitrii Kouznetsov. The free use is allowed.

References

  1. http://www.springerlink.com/content/u712vtp4122544x4/ D.Kouznetsov. Holomorphic extension of the logistic sequence. Moscow University Physics Bulletin, 2010, No.2, p.91-98.
  2. http://www.springerlink.com/content/qt31671237421111/fulltext.pdf?page=1 D.Kouznetsov, H.Trappmann. Superfunctions and square root of factorial. Moscow University Physics Bulletin, 2010, v.65, No.1, p.6-12.
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