Mira's attractor

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rem          Mira’s model
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dim a,b,n,x,y,z,w,xc,yc,zoom,maxiter
x = 15 : y = 0
 a = 0.7 : b = 0.9998 : zoom = 15
' a = 0.8 : b = 0.999 : zoom = 20
' a = 0.85 : b = 0.99978 : zoom = 20
' a = 0.80147 : b = 0.9987 : zoom = 20
' a = -0.48 : b = 0.93 : zoom = 12

w = a*x+(1-a)*2*x*x/(1+x*x)
picture 10 : full_space 10 : 2d_target_is 10 : color 10,0,0,0
xc = width(10)/2-30 : yc = height(10)/2 : maxiter = 10000
for n = 1 to maxiter
    caption 0,"Mira's attractor : Iteration : " + str$(n) + " / " + str$(maxiter) + " ... <ESC> to stop ..."
    z = x : x = b*y+w : w = a*x+(1-a)*2*x*x/(1+x*x) : y = w-z
  '  2d_pen_color mod(n,255),255-mod(n,255), abs(mod(n,255)-255)
    2d_pen_color 255,255,0
    2d_point xc+x*zoom,yc-y*zoom : display
    if scancode = 27 then terminate
next n
caption 0,"Finished !"
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