// rotation.java
// agrarian economy based on land rotation
// adapted from a program in basic by H.T. Odum & E. Odum, 1994

import java.applet.*;
import java.awt.*;

public class rotation extends Applet
{

 Label prompt1, prompt2;
 TextField input1, input2;
 Button drawbutton;
 double dt, a0, s0, q0, b0, i0, a, a1, b, s, q;
 double k0, k1, k2, k3, k4, k5, k6, k7, k8, k9;
 double l1, l2, l3, l4, l5, l6, a2, r, db, ds, da, dq, t, ti;
 double a1i, a2i, bi, si, qi, r0, r1;

 public void init()
 {
 	prompt1 = new Label("S value for wood and soil: ");
	input1 = new TextField("2", 5);
	add(prompt1); add(input1);

	prompt2 = new Label("A1 fallow land: ");
	input2 = new TextField("100", 5);
	add(prompt2); add(input2);

	drawbutton = new Button("Draw");
	add(drawbutton);
 }

 public boolean action(Event e, Object o)
 {
 	s = (float)Integer.parseInt(input1.getText());
 	a1 = (float)Integer.parseInt(input2.getText());
 	repaint();
 	return true;
 }

 public void paint(Graphics g)
 {
 	g.drawRect(0,60,320,250);
	t=0; ti=0;
	dt=3; a0=1; s0=0.5; q0=0.5; b0=0.5; i0=100; a=100; b=100;
	q=10; k0=0.18; k1=0.00008; k2=0.0032; k3=0.004; k4=0.002;
	k5=0.0002; k6=0.0002; k7=0.004; k8=0.00000032; k9=0.002;
	l1=0.0002; l2=0.0002; l3=0.0000002; l4=0.001; l5=0.001; l6=0.00004;
	a1i=0; a2i=0; bi=0; qi=0; si=0;
 	a2=0; r=0;

	//r1=100;
	//do {
	  //r0=r1;
		//r1=i0/(1+k0*r0*a1+k1*s*q*a2);
		//}
	//while ( ((r0-r1)<0.01) && ((r1-r0)<0.01) );
	//r=r1;

	while (t/10<320)
 		{
		a2i=a-a1i;
		r=i0/(1+k0*r*a1+k1*s*q*a2);
		db=k2*r*a1-k3*b-k4*b-k5*b*a1-k9*b;
		ds=k6*b*a1-k7*s-k8*s*r*a2*q;
		da=l1*a2*b-l2*q*a1;
		dq=l3*q*a2*s*r+l4*s-l5*q-l6*a1*q;
		a1i=a1+da*dt;
		if (a1i<0) a1i=0;
		bi=b+(db*dt);
		si=s+(ds*dt);
		qi=q+(dq*dt);
		ti=t+dt;

		g.setColor(Color.red);
		g.drawLine((int)t/10, (int)(310-b*b0), (int)ti/10, (int)(310-bi*b0));
		g.setColor(Color.green);
		g.drawLine((int)t/10, (int)(310-a2*a0), (int)ti/10, (int)(310-a2i*a0));
		g.setColor(Color.blue);
		g.drawLine((int)t/10, (int)(310-s*s0), (int)ti/10, (int)(310-si*s0));
		g.setColor(Color.pink);
		g.drawLine((int)t/10, (int)(310-q*q0), (int)ti/10, (int)(310-qi*q0));
		t=ti; b=bi; a2=a2i; s=si; q=qi;
		}
 }

}
// Camila Duarte & E. Ortega. November 17th 2000