example5_8.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 Example5_8 extends Applet
{
 public double eehmt(double x,double h,int n,double[] y,double[] dy,double t)
 {int i,j;
  double f,l,dl;
  f=0;
  for(i=0;i<n;i++)
  {l=1;dl=0;
   for(j=0;j<i;j++){l*=(t-x-j*h)/(i-j)/h;dl+=1.0/(i-j)/h;}
   for(j=i+1;j<n;j++){l*=(t-x-j*h)/(i-j)/h;dl+=1.0/(i-j)/h;}
   f+=(y[i]+(t-x-i*h)*(dy[i]-2*y[i]*dl))*l*l;}
   return f;
 }

 public void paint(Graphics g)
 {double[] y=new double[11];
  double[] dy=new double[11];
  double f,t;int i;
  for(i=0;i<11;i++){dy[i]=y[i]=Math.exp(i*0.1);}
  for(i=0;i<10;i++)
  {t=Math.random();f=eehmt(0.0,0.1,11,y,dy,t);
   g.drawString("t="+t+"  f(t)="+f+"  实际值="+Math.exp(t),10,20+20*i);}
 }
}