example5_10.java

Java学习丛书科学与工程数值算法（Java版）一书的代码

import java.applet.*;
import java.awt.*;
public class Example5_10 extends Applet
{
 public double eeaitken(double x0,double h,int n,double[] y,double t,double eps)
 {int i,j,k,l;
  double[] p=new double[n];
  int[] s=new int[n];
  i=(int)((t-x0)/h)+1;
  if(i<=0)for(j=0;j<n;j++)s[j]=j;
  else if(i>=n-1)for(j=0;j<n;j++)s[j]=n-1-j;
  else if(t>=x0+i*h-0.5*h)
        { s[0]=i;k=i+1;l=i-1;j=1;
          while(j<n)
          {if(l>=0)s[j++]=l--;
           if(k<n)s[j++]=k++;}
         }
  else
  {s[0]=i-1;l=i-2;k=i;j=1;
   while(j<n)
   {if(k<n)s[j++]=k++;
    if(l>=0)s[j++]=l--;}
   }
  p[0]=y[s[0]];i=0;
  while(++i<n)
  {p[i]=y[s[i]];
   for(j=0;j<i;j++)p[i]=((t-x0-s[j]*h)*p[i]-(t-x0-s[i]*h)*p[j])/(s[i]-s[j])/h;
   if(Math.abs(p[i]-p[i-1])<eps)break;
   }
  return p[i];
 }

 public void paint(Graphics g)
 {double[] y=new double[11];
  double f,t,eps=1e-7;
  int i;
  for(i=0;i<11;i++)y[i]=1.0/(1+0.1*i);
  for(i=0;i<5;i++)
  {t=Math.random()+1;f=eeaitken(1,0.1,11,y,t,eps);
   g.drawString("t="+t+"  f(t)="+f+"  实际值="+1/t,10,20+20*i);}
 }
}