// agrprice.java
// agricultural yield based on relative price
// adapted from a program in basic by H.T. Odum & E. Odum, 1994.

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

public class agrprice extends Applet
{
 Label prompt1,prompt2,prompt3;
 TextField input1,input2,input3;
 float i0,c,f,a,t,p,r,k0,k1,k2,k3,k4,k5,k6,k7,dt,t0,p0,a0,c0,ti,ci,ai,pi,da,dc;

 public void init()
 {
        prompt1 = new Label("Amount of goods and services F (e.g. 4): ");
		input1 = new TextField(10);
		add(prompt1);add(input1);
		prompt2 = new Label("Function of decreasing goods and services (set 0 or 1): ");
		input2 = new TextField(10);
		add(prompt2);add(input2);
		prompt3 = new Label("Environmental inputs (set value between 0 and 10): ");
		input3 = new TextField(10);
		add(prompt3);add(input3);
 }

 public boolean action(Event e, Object o)
 {
        f=(float)Integer.parseInt(input1.getText());
		k7=0.01f*(float)Integer.parseInt(input2.getText());
		i0=0.1f*(float)Integer.parseInt(input3.getText());
		repaint();
		return true;
 }

 public void paint(Graphics g)
 {
        g.drawRect(160,120,320,180);
		g.drawLine(160,200,480,200);
		c=1;a=1000;k0=0.0001f;k1=0.083f;k2=0.00306f;k3=0.025f;t=0;
		k4=0.1f;k5=2f;k6=96.5f;dt=0.2f;t0=3;p0=0.5f;a0=0.005f;c0=10;
		ti=t;ai=a;ci=c;
		pi=k6*f/ci;
		while ((t*t0)<320)
		{
		    r=i0/(1+k0*a);
			p=k6*f/c;
			f=f-k7*f;
			da=p*k5*c-k3*a-k1*r*a;
			dc=k2*r*a-k4*c-k5*c;
			a=a+da*dt;
			c=c+dc*dt;
			g.setColor(Color.blue);
			g.drawLine((int)(160+ti*t0),(int)(300-ci*c0),(int)(160+t*t0),(int)(300-c*c0));
			g.setColor(Color.red);
			g.drawLine((int)(160+ti*t0),(int)(200-ai*a0),(int)(160+t*t0),(int)(200-a*a0));
			g.setColor(Color.green);
			g.drawLine((int)(160+ti*t0),(int)(300-pi*p0),(int)(160+t*t0),(int)(300-p*p0));
			ti=t;ci=c;ai=a;pi=p;
			t+=dt;
		}
	}
}
// Stefan Kontur & Enrique Ortega. September 2000.