// prodsale.java
// economic use of a renewable Source
// adapted from a program in basic by H.T. Odum & E. Odum, 1994

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

public class prodsale extends Applet
{

 Label prompt1, prompt2;
 TextField input1, input2;
 Button drawbutton;
 double j,p1,p2,a,m,e,y,a0,m0,k1,k2,k3,k4,k5,k6,r,da,dm,t,dt,ti,ai,mi;
 int t0;

 public void init()
 {
 	prompt1 = new Label("Start value for M: ");
	input1 = new TextField("200", 5);
	add(prompt1); add(input1);

	prompt2 = new Label("P2 Price for goods and services : ");
	input2 = new TextField("5", 5);
	add(prompt2); add(input2);

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

 public boolean action(Event e, Object o)
 {
 	m = (float)Integer.parseInt(input1.getText());
 	p2 = 0.1f*(float)Integer.parseInt(input2.getText());
 	repaint();
 	return true;
 }

 public void paint(Graphics g)
 {
 	g.drawRect(0,60,320,180);
	g.drawLine(0,150,320,150);
	t=0; t0=3;
	j=1; p1=1; a=0.1; e=100; y=100;
	a0=11; m0=0.07; dt=0.5;
	k1=0.09000001; k2=0.1; k3=0.002; k4=0.01; k5=0.1; k6=10;
	while (t<320)
 		{
		r=j/(1+k1*e*a);
		e=k2*m/p2;
		y=k6*r*e*a;
		da=k3*e-k4*r*e*a-k5*a;
		dm=p1*y-k2*m;
		ai=a+da*dt;
		if (ai<0) ai=0;
		mi=m+dm*dt;
		ti=t+dt;

		g.setColor(Color.red);
	  g.drawLine((int)t*t0, (int) (150-a*a0), (int)ti*t0, (int)(150-ai*a0));
		g.setColor(Color.blue);
	  g.drawLine((int)t*t0, (int) (240-m*m0), (int)ti*t0, (int)(240-mi*m0));
		t=ti;
		m=mi;
		a=ai;

		}
 }
}
// Camila Duarte & E. Ortega, November 13th 2000