; Draws the Lorenz attractor
; Alejandro Luque Estepa, 1999

(import "zlisp.LispMath")
(import "zlisp.LispGraph")


(defun lorenz (a b c dt n)
  (do ( (i 0 (add1 i)) 
	(dx 0.0 (* a (- y x) dt))
	(dy 0.0 (* (- (* b x) y (* z x)) dt)	)
	(dz 0.0 (* (- (* x y) (* c z)) dt))
	(x 1.0 (+ x dx))
	(y 1.0 (+ y dy))
	(z 1.0 (+ z dz)))
      ((> i n) (msg "Lorenz attractor finished" t))
    (color 1.0 0.0 0.0)
    (point (round (+ 70 (* x 7))) (round (+ 100 (* y 7))))
    (color 0.0 1.0 0.0)
    (point (round (+ 410 (* x 7))) (round (+ 20 (* z 7))))
    (color 0.0 0.0 1.0)
    (point (round (+ 150 (* z 7))) (round (+ 100 (* y 7))))
    )
  )



(msg    "lorenz.lisp.txt : zlisp 0.1 Demonstration program" t
	"(lorenz a b c dt N) draws N points of the Lorenz attractor with parameters a, b, c, dt" t
	"Type (lorenz 5.0 15.0 1.0 0.01 5000) to view a chaotic figure" t
)