/*
 * itrap.java - updated 23 May 98 - width 501, height 361
 * @author jackord@kw.igs.net
 * implements Java 1.1 ActionEvent and ActionListener
 */

import java.applet.Applet;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class itrap extends Applet 
                   implements ActionListener {
  int kk=0;                                            // Declarations
  double k, A, m, xa, xb;
  String bs="Run"; Button b=new Button(bs);

  public void init() {
    setLayout(new FlowLayout(FlowLayout.LEFT));
    setBackground(Color.white);
    add(b);
    b.addActionListener(this);
  }

  double vbar(int n) {
    double s, v1, v2, x, dx;
    s=0; x=xa; dx=(xb-xa)/n;
    v1=Math.sqrt(k*(A*A-x*x)/m);
    for (int i=1; i<=n; i=i+1) {
      x=xa+i*dx; v2=Math.sqrt(k*(A*A-x*x)/m);
      s=s+2/(v1+v2); v1=v2;
    }
    return s*dx;
  }

  double trap(int n) {
    double c, s, x, dx;
    s=0; dx=(xb-xa)/n;
    for (int i=0; i<=n; i=i+1) {
      if ((i==0)||(i==n)) { c=.5; } else { c=1; }
      x=xa+i*dx;
      s=s+c/Math.sqrt(k*(A*A-x*x)/m);
    }
    return s*dx;
  }

  public void paint(Graphics g) {
    int x1, y1, x2, y2;
    double x, dx, s1, s2;
    g.setColor(Color.black);
    g.setFont(new Font("TimesRoman", Font.PLAIN, 16));
    g.drawRect(88, 12, 400, 300);
    g.drawString("-5", 85, 332);
    g.drawString("5", 485, 332);
    g.drawString("x  (m)", 268, 344);
    g.drawString("0", 72, 318);
    g.drawString("2", 72, 18);
    g.drawString("1/V(x)", 16, 133); g.drawString("(s/m)", 24, 203);
    if (kk==1) {
      k=1; m=25; A=5; xa=-4; xb=4; dx=(xb-xa)/200;
      g.setColor(Color.blue);
      x1=288+(int)(40*xa); y1=312-(int)(150/Math.sqrt(k*(A*A-xa*xa)/m));
      for (int i=1; i<=200; i=i+1) {
        x=xa+i*dx;
        x2=288+(int)(40*x); y2=312-(int)(150/Math.sqrt(k*(A*A-x*x)/m));
        g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
      }
      g.setColor(Color.magenta); x=xa; dx=(xb-xa)/4;
      x1=288+(int)(40*x); y1=312-(int)(150/Math.sqrt(k*(A*A-x*x)/m));
      g.drawLine(x1, 312, x1, y1);
      for (int i=1; i<=6; i=i+1) {
        x=x+dx;
        x2=288+(int)(40*x); y2=312-(int)(150/Math.sqrt(k*(A*A-x*x)/m));
        g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
        g.drawLine(x1, y1, x1, 312);
        if (i==2) {
          dx=dx/2;
        }
      }
      g.setColor(Color.black); s1=vbar(20); s2=vbar(40);
      g.drawString("Vbar:   T(20) = "+(float)s1+"   T(40) = "+(float)s2+
      "   T = "+(float)(s2+(s2-s1)/3), 100, 32); 
      s1=trap(20); s2=trap(40);
      g.drawString("Trap:   T(20) = "+(float)s1+"   T(40) = "+(float)s2+
      "   T = "+(float)(s2+(s2-s1)/3), 100, 48);
      g.drawString("Analytic:   T = "+(float)(2*Math.sqrt(m/k)*Math.atan(2/1.5)), 220, 80);
    }
    kk=0;
  }

  public void actionPerformed(ActionEvent e) {         // Button
    String tst;
    tst=e.getActionCommand();
    if (bs.equals(tst)) { kk=1; }
    repaint();
  }
}