example6_1.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_1 extends Applet
{
 public static double f(double x)
 {double y;
  y=x*Math.cos(x)+Math.sqrt(x+1);
  return y; }

 public static double traz(double a,double b)
  {double s1,s2=0,h;
   int i,n=1;
   h=b-a;s1=(f(a)+f(b))*h/2;
   while(Math.abs(s1-s2)>1e-7&&Math.abs(h)>1e-7)
   {s1=s2;s2=0;
    for(i=1;i<=n;i++)s2+=f(a+(i-1.0/2)*h);
    s2*=h/2;s2+=s1/2;n*=2;h/=2;
   }
	return s2;
  }

public void paint(Graphics g)
{double y;
 y=traz(-1,2);
 g.drawString("积分值为"+y,10,40);}
}