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Logistic Map--r=4


LogisticEquation4

With r=4, the logistic map becomes

 x_(n+1)=4x_n(1-x_n),
(1)

which is equivalent to the tent map with mu=1. The first 50 iterations of this map are illustrated above for initial values a_0=0.42 and 0.71.

The solution can be written in the form

 x_n=1/2{1-f[r^nf^(-1)(1-2x_0)]},
(2)

with

 f(x)=cosx
(3)

and f^(-1)(x)=cos^(-1)x its inverse function (Wolfram 2002, p. 1098). Explicitly, this then gives the three equivalent forms

x_n=1/2{1-cos[2^ncos^(-1)(1-2x_0)]}
(4)
=1/2{1-cosh[2^ncosh^(-1)(1-2x_0)]}
(5)
=-sinh^2[2^(n-1)cosh^(-1)(1-2x_0)].
(6)

To investigate the equation's properties, let

 x=sin^2(1/2piy)=1/2[1-cos(piy)]
(7)
 sqrt(x)=sin(1/2piy)
(8)
 y=2/pisin^(-1)(sqrt(x)),
(9)

so

 (dy)/(dx)=2/pi1/(sqrt(1-x))1/2x^(-1/2)=1/(pisqrt(x(1-x))).
(10)

Manipulating (7) gives

sin^2(1/2piy_(n+1))=41/2[1-cos(piy_n)]{1-1/2[1-1/2(1-cos(piy_n))]}
(11)
=2[1-cos(piy=1-cos^2(piy_n)sin^2(piy_n),
(12)

so

 1/2piy_(n+1)=+/-y_n+spi
(13)
 y_(n+1)=+/-2y_n+1/2s.
(14)

But y in [0,1]. Taking y_n in [0,1/2], then s=0 and

 y_(n+1)=2y_n.
(15)

For y in [1/2,1], s=1 and

 y_(n+1)=2-2y_n.
(16)

Combining gives

 y_(n+1)={2y_n   for y_n in [0,1/2]; 2-2y_n   for y_n in [1/2,1],
(17)

which can be written

 y_(n+1)=1-2|x_n-1/2|,
(18)

which is just the tent map with mu=1, whose natural invariant in y is

 rho(y)=1.
(19)

Transforming back to x therefore gives

rho(x)=|(dy)/(dx)|rho(y(x))
(20)
=2/pi1/(sqrt(1-x))1/2x^(-1/2)
(21)
=1/(pisqrt(x(1-x))).
(22)

This can also be derived from

 rho(x)=lim_(N->infty)1/Nsum_(i=1)^Ndelta(x_i-x)=1/(pisqrt(x(1-x))),
(23)

where delta(x) is the delta function.


See also

Logistic Map, Logistic Map--r=-2, Logistic Map--r=2, Tent Map

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References

MathPages. "Closed Forms for the Logistic Map." http://www.mathpages.com/home/kmath188.htm. Jaffe, S. "The Logistic Map: Computable Chaos." http://library.wolfram.com/infocenter/MathSource/579/.Whittaker, J. V. "An Analytical Description of Some Simple Cases of Chaotic Behavior." Amer. Math. Monthly 98, 489-504, 1991.Wolfram, S. A New Kind of Science. Champaign, IL: Wolfram Media, p. 1098, 2002.

Cite this as:

Weisstein, Eric W. "Logistic Map--r=4." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/LogisticMapR=4.html

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