// nzealand.java
// trade controlled growth in New Zealand
// adapted from a program in basic by H.T. Odum & E. Odum, 1994

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

public class nzealand extends Applet
{
 Label prompt1,prompt2;
 TextField input1,input2;
 double s,f;
 int t;
 double n,a,j,jn,rp,i;
 double k0,k1,k2,k3,k4,k5,k6,k7,k8,k9;
 double x1,x2,x3,x4,x5;
 double t0,n0,s0,a0,f0,df,dn,da,ds,dt;
 Button drawbutton;

 public void init()
 {
    prompt1 = new Label("F Fuel reserve: ");
	input1 = new TextField("25000",7);
	add(prompt1);add(input1);
	prompt2 = new Label("                    S Stock (sheep and cattle): ");
	input2 = new TextField("1",7);
	add(prompt2);add(input2);
	drawbutton = new Button("Draw");
	add(drawbutton);
 }

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

 public void paint(Graphics g)
 {
    g.drawRect(0,90,320,210);
    n=50; a=10; j=1.1; jn=1; rp=0;
    k0=0.5; k1=1.5; k2=0.15; k3=0.05; k4=1.4; k5=0.0109; k6=0; k7=0.00001;
    k8=0.006; k9=0.02;
    x1=0.0132; x2=0.00013; x3=0.00255; x4=48; x5=0;
	t0=1.5; n0=1; s0=2; a0=0.002; f0=0.00625;
	dt=1; t=0;
	do
	{
	  g.setColor(Color.blue);
	  g.drawOval(t,(int)(300-n*n0),1,1);
      g.setColor(Color.green);
	  g.drawOval(t,(int)(300-s*s0),1,1);
      g.setColor(Color.red);
	  g.drawOval(t,(int)(300-a*a0),1,1);
      g.setColor(Color.yellow);
	  g.drawOval(t,(int)(300-f*f0),1,1);
      i=j/(1+k0*n);
      df=-x5*f;
      dn=jn-k3*n-k4*n*i+x2*a;
      ds=k1*i*n-k2*s-k6*s-k7*s*a;
      da=x5*f+(x4*s+x3*a)*rp+k8*s*a-k9*a-k5*a-x1*a-x3*a;
      a=a+da*dt;
      if (a<1) a=1;
      n=n+dn*dt;
      if (n<0) n=0;
      s=s+ds*dt;
      if (f<0) f=0;
      t=t+1;
      if (t>60) rp=7;
      x4=32;
      k6=0.6;
	  if (t>120) rp=2-0.03*(t-120);
	  x5=x5+0.0001;
	}
	while(t<=320);
  }
}
// Camila Duarte & E. Ortega, January 30h, 2001