The Pickover attractor or Clifford Attractor (named after Clifford A. Pickover) is the system of equations:
xn+1 = sin(a yn) + c × cos(a xn)
yn+1 = sin(b xn) + d × cos(b yn)
Any given set of values for the parameters a, b, c and d defines one specific attractor. They are attractors because the system will evolve to the same pattern for any starting point (x0 , y0).