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Graphic image of the strange attractor of Henon, GWBASIC / BASICA

This short program uses the methods described in James Gleick's book, Chaos, to draw the strange attractor of Henon at 4 magnification levels.

Originally in GWBASIC for the Heathkit H-100 computer, it should work in BASICA on any PC compatible when the SCREEN 12 statement is enabled.

HENON.BAS

10 'HENON.BAS 3-11-90 
11 'COPYRIGHT (C)1990 STEVEN WHITNEY.
12 'Published under GNU GPL (General Public License) Version 3, with ABSOLUTELY NO WARRANTY.
13 'Initially published by http://25yearsofprogramming.com.
14 'EXPERIMENTS WITH HENON'S EQUATIONS RE CHAOS (Chaos, Gleick, page 151).
15 'SCREEN 12 : 'ENABLE FOR IBM BASICA
20 PRINT "PRODUCES GRAPHIC IMAGE OF THE STRANGE ATTRACTOR OF HENON"
30 PRINT "END PROGRAM BY PRESSING CONTROL-C"
40 PRINT
50 INPUT "MAGNIFICATION LEVEL (1-4)"; MAG
60 IF MAG < 1 OR MAG > 4 THEN 50
70 OLDX = .5
80 OLDY = .5
90 IF MAG = 1 THEN WINDOW (-1.2, -.4)-(1.3, .4)
100 IF MAG = 2 THEN WINDOW (0, -.3)-(1.3, .3)
110 IF MAG = 3 THEN WINDOW (.3, 0)-(1.2, .3)
120 IF MAG = 4 THEN WINDOW (1, 0)-(1.2, .15)
130 CLS
140 NEWX = OLDY + 1 - 1.4 * OLDX * OLDX
150 	NEWY = .3 * OLDX
160 	'PRINT NEWX,NEWY
170 	PSET (NEWX, NEWY), 7
180 	OLDX = NEWX: OLDY = NEWY
190 GOTO 140
200 END