[CM] lisp loop iteration in cm

[Juan Reyes]

Hi Rick,

Below is my example for using loop iteration using the Henon Map. If you
change a and b values the algorithm can be more stable or unstable. For
instance a=0.42 and b=-0.99 are also good choices. The initial
conditions x and y of this map can also be changed! 

  --* Juan



;;;; this function maps Henon values to midi note values

(defun midinormz (x)
  (let ((offset 1.0)
	(maxinput 2.0)
	(slope 1.25)
	(maxoutput 127.0)
	(c 0.75)
	(lowbound 15))
    (floor (+ (* (/ (+ x offset) (* maxinput slope))
		 (+ maxoutput c))
	      lowbound)) ))


;;;
;;; Function to generate MIDI notes using the henon map
;;;
;;; http://henon.sapp.org/
;;;

(defun henonseq (cycles rhy dur amp &key
		     (a -1.85039)  ;; a=-1.56693 b= -0.011811
		     (b 0.003937)
		     (x 0.63135448)
		     (y  0.18940634))
  (process repeat cycles
	with newx = 0.00
	with newy = 0.00
	do (progn
	     (setf newx (+ (* a (expt x 2)) (* b y) 1))
	     (setf newy x)
	     (setf x newx)
	     (setf y newy))
	output (new midi :time (now)
		    :duration dur
		    :amplitude amp
		    :keynum (midinormz x))
	wait rhy))

;;; (events (henonseq 12 0.25 0.1 0.7) "henonseq.mid")