/* S0430.java
 *        ポアソン乱数の発生 
 *         (C) H.Ishikawa 2008 
 */

package simulation;

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import window.Window;

public class S0430 extends Applet implements ActionListener {
	Button button0;	
	public void init() {
		button0 = new Button(" 再実行 ");
		add(button0);
		button0.addActionListener(this);
	}
	
	public void actionPerformed(ActionEvent e) {
		String label = e.getActionCommand();
		repaint();
	}

	public void paint(Graphics g){

		Window w ;
		w = new Window();
		int NUMBER  =    10000;
		int SIZE =   20;                /* ヒストグラムの大きさ */
		int j;                          /* forのカウンタ */
		int k;                          /* 本文kの説明参照 */
		int f[] = new int [SIZE];      /* kの頻度 */
		double lambda = 1;              /* λ */
		  
		
		/* グラフィックの準備 */
		int SPACE = 40;
		int HIGHT = 400;
		int WIDTH = 640;
  
		w.setWindow(0,  0.0,0.0,SIZE,0.5,  SPACE,HIGHT-SPACE,WIDTH-SPACE,SPACE);
		w.axis(0, "k", 1, "f[k] / NUMBER", 0.1,g);
	

		/*メイン*/
		for (j = 0; j < NUMBER; j++) {
			k = poisson(lambda);
		    f[k] = f[k] + 1;
		}
		
		/* ヒストグラムを書く */
		g.setColor(Color.red);
		for (k = 0; k < SIZE; k ++)  {
			w.line(0, k + 0.5, 0, k + 0.5, (double)f[k] / NUMBER, g);
		}
		
	}
	
	int poisson(double lambda)	{
		double xp;
		int k = 0;
		xp = Math.random();
		while (xp >= Math.exp(-lambda)) {
			xp = xp * Math.random();
			k = k + 1;
		}
		return (k);
	}
}