Originally proposed by Kensuke Ikeda as a model of light going around across a nonlinear optical resonator (laser pulse dynamics). t_n = 0.4 - 6.0 / (1 + x_n² + y_n²) x_{n+1} = 1 + u (x_n cos(t_n) - y_n sin(t_n))
When parameter `u = 0.9`, it forms a beautiful strange attractor. As the simulation runs, the density map builds up an ASCII nebula of intersecting light paths.