Peter de Jong Attractors
Written by Paul Bourke
January 1991, Images updated February 2014
See "The Pattern Book, Fractals, Art, and Nature"
by Clifford Pickover, chapter titled "Swirl".
Contribution by Robert Rodger.
Evaldraw script: attract.kc

x_{n+1} = sin(a y_{n})  cos(b x_{n})
y_{n+1} = sin(c x_{n})  cos(d y_{n})

a = 1.4, b = 2.3, c = 2.4, d = 2.1
a = 2.01, b = 2.53, c = 1.61, d = 0.33
a = 2.7, b = 0.09, c = 0.86, d = 2.2
a = 2.24, b = 0.43, c = 0.65, d = 2.43
a = 2, b = 2, c = 1.2, d = 2
Contribution by Johnny Svensson
A variation:
x_{n+1} = d sin(a x_{n})  sin(b y_{n})
y_{n+1} = c cos(a x_{n}) + cos(b y_{n})
The one ring
a = 1.40, b = 1.56, c = 1.40, d = 6.56
