Hey,

I'm  learning about strange attractors and the book I'm reading has QBasic examples of graphing 2D functions.  I'm trying to convert one of the examples to Processing, but I keep stumbling over myself. Maybe I am missing boundary checks?

Any help would be greatly appreciated!

Thanks.

1. ///
   int prev = 5;
   int nmax = 11000;
   int omax = 2;
   int d = 2;
   float xmin;
   float xmax;
   float ymin;
   float ymax;
   float xp, yp;
   
   float x, y;
   float x2,y2;
   
   int n;
   int nl;
   float lsum;
   float l;
   
   float xh,xl,yh,yl;
   float xe,ye;
   
   float []coeffs;
   PFont font;
   
   void setup() {
     size(500,500);
     background(255);
     font = loadFont("MonotypeSorts-9.vlw");
     textFont(font, 9);
     setparm();
   }
   
   void draw() {
     fill(255);
     stroke(255);
     rect(width/2, 0, width, 20);
     fill(0);
     text("L: "+l, width-100, 15);
   
   
     iterate();
     display();
     test();
   }
   
   void setparm() {
     x = 0.5;
     y = 0.5;
     xe = x + .000001;
     ye = y;
     coeffs = getCoeff();
     lsum = 0;
     n = 0;
     l =0;
     nl = 0;
     xmin = 1000000;
     xmax = -xmin;
     ymin = xmin;
     ymax = xmax;
   }
   
   float[] getCoeff() {
     int o = 2 + int((omax - 1) * random(0,1));
     float m = 1;
     String code = "";
     code += char(59 + 4 * d + o);
   
     for(int i = 1; i <= d;i++){
       m = m * (o+i);
     }
   
     for(int i = 1; i <= m; i++) {
       code += char(65 + int(25 * random(0,1)));
     }
   
     println("Reset!");
     float []a = new float[(int)m];
     for(int i = 0; i < m; i++) {
       a[i] = int(code.charAt(i))-77;
       a[i] = a[i]/10;
       print(a[i]+" ");
     }
     println();
     fill(255);
     stroke(255);
     rect(0, 0, width/2, 20);
     fill(0);
     text(code, 5, 16);
     return a;
   }
   
   
   void iterate() {
     x2 = coeffs[0] + x * (coeffs[1] + coeffs[2] * x + coeffs[3] * y) + y * (coeffs[4] + coeffs[5] * y);
     y2 = coeffs[6] + x * (coeffs[7] + coeffs[8] * x + coeffs[9] * y) + y * (coeffs[10] + coeffs[11] * y);
     println(++n+" x:"+x+" x2:"+x2+" y:"+y+" y2:"+y2);
   }
   /*
   1700 REM Iterate equations
    1720 XNEW = A(1) + X * (A(2) + A(3) * X + A(4) * Y)
    1730 XNEW = XNEW + Y * (A(5) + A(6) * Y)
    1830 YNEW = A(7) + X * (A(8) + A(9) * X + A(10) * Y)
    1930 YNEW = YNEW + Y * (A(11) + A(12) * Y)
    2020 N = N + 1
    2030 RETURN*/
   
   void display() {
     if( !(n < 100) && !(n > 1000) ) {
       if( x < xmin ) xmin = x;
       if( x > xmax ) xmax = x;
       if( y < ymin ) ymin = y;
       if( y > ymax ) ymax = y;
     }  
     if( n == 1000 )
       resizescreen();
   
     if( n < 1000 || x <= xl || x >= xh || y <= yl || y >= yh ){
     }
     else {
       fill(0);
       point(width * (x-xl)/(xh-xl),height*(yh-y)/(yh-yl));
       println("x="+(width * (x-xl)/(xh-xl))+" y="+(height*(yh-y)/(yh-yl)));
     }
   }
   /*
   2100 REM Display results
    2110 IF N < 100 OR N > 1000 THEN GOTO 2200
    2120    IF X < XMIN THEN XMIN = X
    2130    IF X > XMAX THEN XMAX = X
    2140    IF Y < YMIN THEN YMIN = Y
    2150    IF Y > YMAX THEN YMAX = Y
    2200 IF N = 1000 THEN GOSUB 3100        'Resize the screen
    2210 XS(P%) = X
    2220 P% = (P% + 1) MOD 500
    2230 I% = (P% + 500 - PREV%) MOD 500
    2240 IF D% = 1 THEN XP = XS(I%): YP = XNEW ELSE XP = X: YP = Y
    2250 IF N < 1000 OR XP <= XL OR XP >= XH OR YP <= YL OR YP >= YH THEN GOTO 2320
    2300    PSET (WW * (XP - XL) / (XH - XL), WH * (YH - YP) / (YH - YL))
    2310    IF SND% = 1 THEN GOSUB 3500     'Produce sound
    2320 RETURN
    */
   void resizescreen() {
     if( xmax - xmin < .000001 ) {
       xmin -= .0000005;
       xmax += .0000005;
     }
     if( ymax - ymin < .000001 ) {
       ymin -= .0000005;
       ymax += .0000005;
     }
     float mx = .1 * (xmax - xmin);
     float my = .1 * (ymax - ymin);
     xl = xmin - mx;
     xh = xmax + mx;
     yl = ymin - my;
     yh = ymax + my;
   }
   /*3100 REM Resize the screen
    3110 IF D% = 1 THEN YMIN = XMIN: YMAX = XMAX
    3120 IF XMAX - XMIN < .000001 THEN XMIN = XMIN - .0000005: XMAX = XMAX + .0000005
    3130 IF YMAX - YMIN < .000001 THEN YMIN = YMIN - .0000005: YMAX = YMAX + .0000005
    3160 MX = .1 * (XMAX - XMIN): MY = .1 * (YMAX - YMIN)
    3170 XL = XMIN - MX: XH = XMAX + MX: YL = YMIN - MY: YH = YMAX + MY
    3180 WW = WINDOW(2): WH = WINDOW(3): BUTTON CLOSE 0: CLS
    3460 RETURN*/
   
   void test() {
     if( abs(x2) + abs(y2) > 1000000 ) {
       setparm();
     }
     else {
       calc();
   
       if( (n >= nmax) ) {
         println("!st");
         setparm();
       }
   
       if(n > 100 && l < .005) {
         println("2nd");
         setparm();
       }
       if((abs(x2-x) + abs(y2-y)) < .000001) {
         println("3rd");
         setparm();
       }
       x = x2;
       y = y2;
     }
   }
   /*
   2400 REM Test results
    2410 IF ABS(XNEW) + ABS(YNEW) > 1000000! THEN T% = 2    'Unbounded
    2430 GOSUB 2900                 'Calculate Lyapunov exponent
    2460 IF N >= NMAX THEN T% = 2   'Strange attractor found
    2470 IF ABS(XNEW - X) + ABS(YNEW - Y) < .000001 THEN T% = 2
    2480 IF N > 100 AND L < .005 THEN T% = 2    'Limit cycle
    2490 Q$ = INKEY$: IF LEN(Q$) THEN GOSUB 3600        'Respond to user command
    2500 IF MENU(0) = 2 AND MENU(1) = 1 THEN Q$ = "S": GOSUB 3600
    2510 X = XNEW                   'Update value of X
    2520 Y = YNEW
    2550 RETURN
    */
   
   void calc() {
     float xsave = x2;
     float ysave = y2;
     x = xe;
     y = ye;
     n--;
     iterate();
     float dlx = x2 - xsave;
     float dly = y2 - ysave;
     float dl2 = dlx*dlx + dly * dly;
     if( (int)dl2 > 0 ) {
       println("tab");
       float df = 1000000000000L * dl2;
       float rs = 1 / sqrt(df);
       xe = xsave + rs * (x2 - xsave);
       ye = ysave + rs * (y2 - ysave);
       x2 = xsave;
       y2 = ysave;
       if( df > 0 ) {
         lsum = lsum + log(df);
         nl++;
       }
       l = .721347 * lsum / nl;
     }
   }/*
   2900 REM Calculate Lyapunov exponent
    2910 XSAVE = XNEW: YSAVE = YNEW: X = XE: Y = YE: N = N - 1
    2930 GOSUB 1700                 'Reiterate equations
    2940 DLX = XNEW - XSAVE: DLY = YNEW - YSAVE
    2960 DL2 = DLX * DLX + DLY * DLY
    2970 IF CSNG(DL2) <= 0 THEN GOTO 3070       'Don't divide by zero
    2980    DF = 1000000000000# * DL2
    2990    RS = 1 / SQR(DF)
    3000    XE = XSAVE + RS * (XNEW - XSAVE): YE = YSAVE + RS * (YNEW - YSAVE)
    3020    XNEW = XSAVE: YNEW = YSAVE
    3030    IF DF > 0 THEN LSUM = LSUM + LOG(DF): NL = NL + 1
    3040    L = .721347 * LSUM / NL
    3070 RETURN*/
   
   

The example code: http://sprott.physics.wisc.edu/fractals/bookdisk/PROG06QB.MAC

[EDIT] Modified some of the code, but still doesnt work.