//  Simpson則による数値積分 sqrt(4.0-x^2) x=0〜2.0

/* <applet code="Ex060923c" width=300 height=100> </applet> */
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Ex060923c extends JApplet implements ActionListener{
	JLabel lb1,lb2;
	JTextField tf ;
	Ex060923c_Simpson intg;
	public void init(){
		Container cp = getContentPane();
		JPanel pl = new JPanel();
		int num; // 分割数
  	lb1 = new JLabel("分割数=");
    lb2 = new JLabel("計算値=");		
		tf = new JTextField(20);
 		tf.addActionListener(this);
   	pl.add(lb1);
    pl.add(tf);
    pl.add(lb2);
  	cp.add(pl);
  }
	public void actionPerformed(ActionEvent event){
		int num = Integer.valueOf(tf.getText()).intValue();
		intg = new Ex060923c_Simpson(0,2.0,num);
		lb2.setText("計算値= "+intg.calc());
	}
}

// Simpson則による数値積分
class Ex060923c_Simpson{
	double xf; // 積分開始値
	double xl; // 積分終了値
	int num ; // 分割数
	double h;
	Ex060923c_Simpson(double x0, double x1){
		xf=x0;
		xl=x1;
		num = 100; 
		h = (x1-x0)/(double)num;
	}
	Ex060923c_Simpson(double x0, double x1, int num){
		xf=x0;
		xl=x1;
		this.num=num; 
		h = (x1-x0)/(double)num;
	}
	
	double calc(){
		double f0,f1,f2;
		double x0,x1,x2;
		double val=0.0;
		x0=xf;
		f0=func(x0);
		for(x1=h;x1<xl-h;x1=x1+2.0*h){
			x2=x1+h;
			f1=func(x1);
			f2=func(x2);
			val+=h*(f0+4.0*f1+f2)/3.0;
			f0=f2;
		}
		return(val);
	}
		
	double func(double x){
		return( Math.sqrt(4.0-x*x) );// 積分関数の定義
	}
}