// people.java
// world population
// adapted from a program in basic by H.T. Odum & E. Odum, 1994

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

public class people extends Applet
{
    double j,i,n,a,r,k0,k1,k2,k3,k4,k5,k6,k7,k8,k9,l1,l0,t0,n0,f0,a0,x;
	double ni,ai,fi,ti,df,da,b,d,t,fd;
	int k8i,k9i,f;

	Label prompt1, prompt2, prompt3;
	TextField input1, input2, input3;
	Button drawbutton;

	public void init()
	{
     prompt1 = new Label("Enter a start value for F :");
	 input1 = new TextField("900",6);
	 add(prompt1);add(input1);

	 prompt2 = new Label("K9 Value for medical care :");
	 input2 = new TextField("9000",16);
	 add(prompt2);add(input2);

	 prompt3 = new Label("K8 Value of epidemics :");
	 input3 = new TextField("4116",6);
	 add(prompt3);add(input3);

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

	public boolean action (Event event,Object o)
	{
	    if (event.target == input3 || event.target == input2 || event.target ==input1) {
  		f=Integer.parseInt(input1.getText());
		fd=(float)f;
	 	k9i=Integer.parseInt(input2.getText());
		k8i=Integer.parseInt(input3.getText());
		repaint();
	}

	return true;
  }

  public void paint ( Graphics g )
  {
	    j=8.560001;i=5;n=5;a=1;r=12.5;
		k0=0.00003;k1=0.0000176;k2=0.01;k3=0.0000176;k4=0.01;
		k5=0.05;k6=0.0135;k7=0.126;
		l1=0.001054;l0=0.0433;t0=2.8;n0=0.08;f0=16;a0=1.8;x=1;
		ni=5;ai=1;fi=1000;ti=0;t=0;
		g.drawRect(0,90,320,180);
		g.drawLine(0,150,320,150);

		k8=(float)k8i/1000000.f;
		k9=(float)k9i/1000000.f;

		while (t/t0<320)
		{
	  	 r=j/(1+k1*fd*n*a+k2*a);
	  	 df=-k0*r*fd*n*a;
	  	 da=k3*r*n*fd*a+k4*r*a-k5*a-k6*a-l0*n*n*(1-k9*a);
	  	 b=l1*(a/n)*n;
	  	 d=k7*n*(1-k9*a)+k8*n*n*(1-k9*a);
	  	 if (d<0) d=0;
	  	 fd=fd+df*i*x;
	  	 if (fd<1) fd=1;
	  	 n=n+(b-d)*i;
	  	 if (n<0.01) n=0.01;
	  	 a=a+da*i;
	  	 if (a<1) a=1;
	  	 g.setColor(Color.blue);
		 g.drawLine((int)(ti/t0),(int)(270-ni/n0),(int)(t/t0),(int)(270-n/n0));
		 g.setColor(Color.red);
		 g.drawLine((int)(ti/t0),(int)(270-ai/a0),(int)(t/t0),(int)(270-a/a0));
		 g.setColor(Color.green);
		 g.drawLine((int)(ti/t0),(int)(150-fi/f0),(int)(t/t0),(int)(150-fd/f0));
		 ti=t;
		 ni=n;
		 ai=a;
		 fi=fd;
		 t+=i;
	    }
	}
}
// Stefan Kontur & E. Ortega. August 28th 2000