// foryield.java
// forest yield
// adapted from a program in basic by H.T. Odum & E. Odum, 1994.

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

public class foryield extends Applet
{
  double j0,p1,p2,p3,sw,w,m,tw,tc,k0,k1,k2,k3,k4,k5,k6,k7,k8,k9,l1,dt,t0,m0,w0,s0,t,ge,r,dw,ds,dm,x,wi,mi,swi,ti;
  Label pr1,pr2,pr3,pr4;
  TextField in1,in2,in3,in4;

  public void init()
  {
	    pr1 = new Label("Value for environmental input (e.g.10): ");
		in1 = new TextField("10",4);
		add(pr1);add(in1);
		pr2 = new Label("Price of wood (e.g.65): ");
		in2 = new TextField("65",2);
		add(pr2);add(in2);
		pr3 = new Label("Rate of fertilization (e.g.40): ");
		in3 = new TextField("40",2);
		add(pr3);add(in3);
		pr4 = new Label("Theshold of cutting (e.g.2000): ");
		in4 = new TextField("2000",4);
		add(pr4);add(in4);
  }

  public boolean action (Event e, Object o)
  {
	j0=0.1*(double)Integer.parseInt(in1.getText());
	p1=0.0001*(double)Integer.parseInt(in2.getText());
	k8=0.001*(double)Integer.parseInt(in3.getText());
	tw=(float)Integer.parseInt(in4.getText());
	repaint();
	return true;
  }

  public void paint (Graphics g)
  {
	p2=1;p3=0.2;sw=2;w=100;m=10;
	tc=200;k0=0.00283;k1=0.66;k2=0.05;
	k3=0.000066;k4=0.03;k5=1;k6=0.2;k7=0.4;
	k9=0.00065;l1=0.05;dt=0.2;t0=5;m0=2;
	w0=0.02;s0=20;t=0;
	swi=2;mi=10;wi=100;ti=0;
	g.drawRect(60,160,320,180);
	g.drawLine(60,240,380,240);
	while ((t*t0)<320)
	{
	    ge=k6*m/p3;
		if (w>tw)  x=1;
		if (w<tc)  x=0;
		r=j0/(1+k0*sw*w);
		dw=k1*r*sw*w-k2*w-x*k5*w;
		ds=k8*ge-k3*r*sw*w-k4*sw;
		dm=x*k5*p1*w-x*k9*w*p2-k9*m-l1*m-k6*m;
		sw=sw+ds*dt;
		if (sw<0) sw=0;
		w=w+dw*dt;
		if (w<10) w=10;
		m=m+dm*dt;
		g.setColor(Color.blue);
		g.drawLine((int)(60+ti*t0),(int)(340-wi*w0),(int)(60+t*t0),(int)(340-w*w0));
		g.setColor(Color.red);
		g.drawLine((int)(60+ti*t0),(int)(240-mi*m0),(int)(60+t*t0),(int)(240-m*m0));
		g.setColor(Color.green);
		g.drawLine((int)(60+ti*t0),(int)(320-swi*s0),(int)(60+t*t0),(int)(320-sw*s0));
		ti=t;
		t+=dt;
		mi=m;wi=w;swi=sw;
	}
  }
}
// Stefan Kontur & E. Ortega. September, 2000.