A..3.1 NewHeat1D.java

まずはダブル・バッファリングを使うバージョン NewHeat1D.java (実行は http://nalab.mind.meiji.ac.jp/~mk/labo/java/sample/NewHeat1D.html) から。

   1 /*
   2  * NewHeat1D.java
   3  * 2005/12/26
   4  *
   5  * コンパイル: javac NewHeat1D.java
   6  * 実行:       java NewHeat1D
   7  *
   8  * ダブルバッファリングを利用。一度しか計算しない。
   9  * 
  10  */
  11 
  12 import java.awt.Frame;
  13 import java.awt.Graphics;
  14 import java.awt.Image;
  15 import java.awt.event.WindowAdapter;
  16 import java.awt.event.WindowEvent;
  17 
  18 
  19 public class NewHeat1D extends Frame {
  20     Image im = null;
  21     Graphics g2 = null;
  22     int i, n, nMax;
  23     int N = 40;
  24     double lambda = 0.5;
  25     double Tmax = 10.0;
  26     double dt = 0.01;
  27     double h, tau;
  28     int skip;
  29     double [] u, newu;
  30     double ratiox, ratioy, X0, Y0;
  31     public NewHeat1D() {
  32         this.setSize(500, 500);
  33         this.addWindowListener(new WindowAdapter() {
  34                 public void windowClosing(WindowEvent ev) {
  35                     System.exit(0);
  36                 }
  37             });
  38         this.setVisible(true);
  39     }
  40     public static void main(String[] args) {
  41         // TODO 自動生成されたメソッド・スタブ
  42         new NewHeat1D();
  43     }
  44     private void space(double x0, double y0, double x1, double y1) {
  45         X0 = x0; Y0 = y0;
  46         ratiox = 500 / (x1 - x0);
  47         ratioy = 500 / (y1 - y0);
  48     }
  49     private int wx(double x) {
  50         return (int)(ratiox * (x - X0));
  51     }
  52     private int wy(double y) {
  53         return 500 - (int)(ratioy * (y - Y0));
  54     }
  55     private double f(double x) {
  56         if (x <= 0.5)
  57             return x;
  58         else
  59             return 1.0 - x;
  60     }
  61     public void paint(Graphics g) {
  62         if (im == null) {
  63             im = this.createImage(this.getWidth(), this.getHeight());
  64             g2 = im.getGraphics();
  65             space(-0.1, -0.1, 1.1, 1.1);
  66             h = 1.0 / N;
  67             tau = lambda * h * h;
  68             skip = (int)Math.rint(dt / tau);
  69             nMax = (int)Math.rint(Tmax / tau);
  70             u = new double [N+1];
  71             newu = new double [N+1];
  72             // 初期値
  73             for (i = 0; i <= N; i++)
  74                 u[i] = f(i * h);
  75             // 初期値のグラフを描く
  76             for (i = 0; i < N; i++)
  77                 g2.drawLine(wx(i * h), wy(u[i]), wx((i + 1) * h), wy(u[i+1]));
  78             // 時間発展
  79             for (n = 1; n <= nMax; n++) {
  80                 // 陽的差分法
  81                 for (i = 1; i < N; i++)
  82                     newu[i] = (1 - 2 * lambda) * u[i] + lambda * (u[i + 1] + u[i - 1]);
  83                 for (i = 1; i < N; i++)
  84                     u[i] = newu[i];
  85                 // 同次Dirichlet境界条件
  86                 u[0] = 0.0;
  87                 u[N] = 0.0;
  88                 // 時刻が dt の整数倍のときにグラフを描く
  89                 if (n % skip == 0) {
  90                     for (i = 0; i < N; i++)
  91                         g2.drawLine(wx(i * h), wy(u[i]), wx((i + 1) * h), wy(u[i+1]));
  92                 }
  93                 System.out.println(""+ n * tau);
  94             }
  95         }
  96         g.drawImage(im, 0, 0, this);
  97     }
  98 }