Peter de Jong Attractor:
Xn+1 = sin(a * Yn) - cos(b * Xn)
Yn+1 = sin(c * Xn) - cos(d * Yn)
Clifford Attractor:
Xn+1 = sin(a * Yn) + c * cos(a * Xn)
Yn+1 = sin(c * Xn) + d * cos(b * Yn)
u/clockywork modification of Clifford Attractor
x[n] = (sin(a * y[n-1]))^2 + c * (cos(a * x[n-1]))^2
y[n] = (sin(b * x[n-1]))^2 + d * cos(b * y[n-1]) * cos(a * x[n-1])
Original published source in Computer Recreations, Scientific American, July 1987
http://paulbourke.net/fractals/peterdejong/
http://paulbourke.net/fractals/clifford/