//-------------------------------------------------C
// 偏微分方程式の差分解法　例題                     C
//  P21  図1.8, 図1.9, 図1.10, 図1.11-(a),(b)      C
//  2009年4月25日　後 保範（早稲田大学）            C
//-------------------------------------------------C
import java.awt.*;
import javax.swing.*;  

public class Ex1 extends JPanel{
   public Ex1(){  
      setBackground(Color.white);
      setPreferredSize(new Dimension(650, 650));
   }
   protected void paintComponent(Graphics g){
      super.paintComponent(g); 
      double D, DT, DX, DTX;
      double U[][] = new double[30][65];
      double X[] = new double[65];
      int X1, X2, U1, U2, k, t;
      int n, m, l, R=3;
      int XC=50, XV=500, UC=500, UV=-500;
//-----------------------------------------------C
//   図1.8
//      n=8; m=3; l=2; DT=1/(20.0*n); DX=1.0/n;
//   図1.9
//      n=16; m=6; l=1; DT=1/(20.0*n); DX= 1.0/n;
//   図1.10
//      n=16; m=12; l=2; DT=1/(40.0*n); DX =1.0/n;
//   図1.11-(a)
      n=8; m=2; l=2; DT=3/(40.0*n); DX =1.0/n;
//   図1.11-(b)
//      n=16; m=8; l=2; DT=3/(80.0*n); DX =1.0/n;
//-----------------------------------------------C
      DTX = DT/(DX*DX);
      D = 1.0/n;
//  set initial (t=0)
      for (k=0; k<n/2; k++)
        { X[k] = D*k; U[0][k] = X[k]; }
      for (k=n/2; k<=n; k++)
        { X[k] = D*k; U[0][k] = 1.0 - X[k]; }
//  Compute t=D -- 5*D
      for (t=0; t<=l*m-1; t++)
        { U[t+1][0] = U[t+1][n] = 0;
          for (k=1; k<n; k++)
            { U[t+1][k] = U[t][k] + DTX*( U[t][k+1] 
                        - 2*U[t][k] + U[t][k-1] ); }
        }
//  Draw Axis
      g.drawLine(XC, UC, 2*XC+XV, UC);
      g.drawLine(XC+XV, UC, XC+XV, UC+10);
      g.drawLine(XC, UC, XC, XC);
      g.drawLine(XC, UC+UV/2, XC-10, UC+UV/2);
//  Draw Line
      g.setColor(Color.blue); 
      g.fillOval(XC-R, UC-R, 2*R, 2*R);    
      for (t=0; t<=l*m; t+=m) 
        { for (k=1; k<=n; k++)
           { X1 = (int)(X[k-1]*XV) + XC;
             X2 = (int)(X[k]*XV) + XC;
             U1 = (int)(U[t][k-1]*UV) + UC;
             U2 = (int)(U[t][k]*UV) + UC;
             g.drawLine(X1, U1, X2, U2); 
             g.fillOval(X2-R, U2-R, 2*R, 2*R);  }
        }
   }
   public static void main(String[] args){
      JFrame frame = new JFrame("Draw Line");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      Ex1 h = new Ex1();
      frame.add(h, BorderLayout.CENTER);
      frame.pack(); 
      frame.setVisible(true);
   }
}