// econuse.java
// environmental resource and the economic use loop
// adapted from a program in basic by H.T. Odum & E. Odum, 1994.

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

public class econuse extends Applet
{

  Label prompt1,prompt2,prompt3;
  TextField input1,input2,input3;
  double pg,i0,pe;
  Button drawbutton;

  public void init()
  {
	    prompt1 = new Label("PG Price of soods and services: ");
		input1 = new TextField("2",4);
		add(prompt1);add(input1);

		prompt2 = new Label("I0 Environmental resource: ");
		input2 = new TextField("100",4);
		add(prompt2);add(input2);

		prompt3 = new Label("PE Price for product: ");
		input3 = new TextField("1",4);
		add(prompt3);add(input3);

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

  public boolean action(Event e, Object o)
  {
	    pg=(float)Integer.parseInt(input1.getText());
		i0=(float)Integer.parseInt(input2.getText());
	    pe=(float)Integer.parseInt(input3.getText());
		repaint();
		return true;
  }

  public void paint(Graphics g)
  {
        int t;
		double q,a,m,r,i;
		double k0,k1,k2,k3,k4,k5,k6,k7;
		double t0,q0,a0,m0,dt,dq,da,dm;
		q=10;a=10;m=10;
		k0=0.19;k1=0.002;k2=0.005;k3=0.00005;k4=0.0001;k5=0.01;k6=0.003;k7=0.000005;
		dt=10;t0=0.1;q0=0.5;a0=0.3;m0=0.3;t=0;
		g.drawRect(0,90,320,210);

		do
		{
		  g.setColor(Color.blue);
		  g.drawOval(t,(int)(300-q*q0),1,1);
          g.setColor(Color.green);
		  g.drawOval(t,(int)(300-a*a0),1,1);
          g.setColor(Color.red);
          g.drawOval(t,(int)(300-m*m0),1,1);
          r=i0/(1+k0*q);
          i=k4*q*a;
          dq=k1*r*q-k2*q-k3*q*a;
          da=k5*m/pg-k6*a-k7*q*a;
          dm=pe*i-k5*m;
          a=a+da*dt;
          q=q+dq*dt;
          m=m+dm*dt;
          t=t+1;
		}
		while(t<=320);
	 }
	}
// Camila Duarte & E. Ortega. January 29th, 2001