example6_3.java

清华大学2002年出版的《科学与工程数值计算算法Java》配套源码

import java.applet.*;
import java.awt.*;


public class Example6_3 extends Applet
{
 public static double f(double x)
 {double y;
  y=Math.exp(x);
  return y; }

 public static double test(double a,double b,double  eps)
  {double  s1,s2;
   s1=(f(a)+f(b))*(b-a)/2;
   s2=s1/2+f((a+b)/2)*(b-a)/2;
   if(Math.abs(s1-s2)<3*eps)return s2;
   else
   {s1=test(a,(a+b)/2,eps/2);
    s2=test((a+b)/2,b,eps/2);
    return (s1+s2);
   }
}
public void paint(Graphics g)
{double y,eps=1e-7;
 y=test(0,10,eps);
 g.drawString("积分近似值为"+y,10,20);
}
}