/*
 * gd2.java - revised 15 Apr 05 - width 257, height 257
 * @author jackord@kw.igs.net
 * solution of Laplace's equation for concentric square prisms sides L and 2L
 *   relaxation calculation with 5120 passes
 *   the field is plotted after 20 passes, and whenever the number
 *     of passes doubles thereafter
 *   the capacitance is calculated using Gauss's law and is expressed as a
 *     multiple of that of a cylindrical capacitor with diameters L and 2L
 */

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

public class gd2 extends Applet 
                    implements ActionListener {
  int kk=0;                                            // Declarations
  String bs="Plot"; Button b = new Button(bs);
  TextField tx1=new TextField(16);
  TextField tx2=new TextField(16);
  Color col[]={ Color.blue, Color.cyan, Color.red, Color.yellow, Color.magenta, Color.green };

  public void init() {                                 // Layout
    add(b); add(tx1); add(tx2);
    b.addActionListener(this);
    setBackground(new Color(211, 211, 211));
    tx1.setBackground(getBackground());
    tx2.setBackground(getBackground());
  }

  public void paint(Graphics g) {                      // Main Program
    b.setBounds(108, 118, 40, 20);                     // Revise layout
    tx1.setBounds(78, 86, 100, 20);
    tx1.setText("Pass    /5120");
    tx2.setBounds(78, 150, 100, 20);
    tx2.setText("Csqr/Ccir  ");
    int n=64;
    double s, e;
    double [][] v=new double[130][65];
    g.setColor(Color.blue); g.drawRect(0, 0, 256, 256);
    g.setColor(col[(int)(100/7)%6]); g.drawRect(64, 64, 128, 128);
    if (kk==1) {
      for (int i=n; i<=2*n; i=i+1) {                   // Define V on boundary
        v[i][n]=100;                                   // .. default is 0
      }
      for (int j=1; j<=n-1; j=j+1) {                   // Initial linear distn
        for (int i=j; i<=2*n; i=i+1) {
          v[i][j]=100.*j/n;
        }
      }
      int k=1;
      for (int ii=0; ii<=5121; ii=ii+1) {              // Main loop
        for (int j=1; j<=n-1; j=j+1) {                 // Project across bdry
          v[j][j+1]=v[j+1][j]; v[2*n+1][j]=v[2*n-1][j];
        }
        if ((ii==0)||(ii==10*k)) {
          tx1.setText("Pass "+ii+"/5120");
          for (int j=1; j<=n-1; j=j+1) {               // Plot potential..
            for (int i=j; i<=2*n; i=i+1) {
              g.setColor(col[(int)(v[i][j]/7)%6]);
              g.drawLine(i, j, i, j);                  // ..in
              g.drawLine(4*n-i, j, 4*n-i, j);          // ..all
              g.drawLine(j, i, j, i);                  // ..eight
              g.drawLine(j, 4*n-i, j, 4*n-i);          // ..symmetry
              g.drawLine(4*n-j, i, 4*n-j, i);          // ..related
              g.drawLine(4*n-j, 4*n-i, 4*n-j, 4*n-i);
              g.drawLine(i, 4*n-j, i, 4*n-j);
              g.drawLine(4*n-i, 4*n-j, 4*n-i, 4*n-j);  // ..regions
            }
          }
          int j=n/2; s=0; e=0;                         // Calculate C
          for (int i=j; i<=2*n; i=i+1) {               // Gauss's Law
            e=v[i][j]-v[i][j-1]; s=s+e;
          }
          s=s-e/2; s=s*8/100/4/Math.PI; s=s*2*Math.log(2);
          s=(int)(1000*s)/1000.;
          tx2.setText("Csqr/Ccir  "+s);                // Display C ratio
          k=2*k;                                       // Double plot interval
        }
        for (int j=1; j<=n-1; j=j+1) {                 // The calculation!
          for (int i=j; i<=2*n; i=i+1) {
            v[i][j]=(v[i][j-1]+v[i][j+1]+v[i-1][j]+v[i+1][j])/4;
          }
        }
      }
      tx1.setText("    Finished");
      kk=0;
    }
  }

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