example5_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 Example5_1 extends Applet
{
 public double enlgr(double[] x,double[] y,double t)
  {int i,j,k,l,n=x.length;
   double s,f;
   for(i=0;i<n;i++)
   {if(t==x[i])return y[i];
    if(t<x[i])break;}
   if(i<4){k=0;l=i+4;}
   else if(i>=n-4){k=i-4;l=n;}
   else {k=i-4;l=i+4;}
   f=0;
   for(i=k;i<l;i++)
   {s=1;
 	for(j=k;j<i;j++)s*=(t-x[j])/(x[i]-x[j]);
 	for(j=i+1;j<l;j++)s*=(t-x[j])/(x[i]-x[j]);
 	f+=s*y[i];
   }
   return f;
   }

  public double enlgr2(double[] x,double[] y,double t)
  {int i,j,n=x.length;
   double s,g=0;
   for(i=0;i<n;i++)
   {s=1;
    for(j=0;j<i;j++)s*=(t-x[j])/(x[i]-x[j]);
    for(j=i+1;j<n;j++)s*=(t-x[j])/(x[i]-x[j]);
    g+=s*y[i];}
   return g;}

 public void paint(Graphics g)
 {double[] x={0.10,0.15,0.25,0.40,0.50,0.57,0.75,0.85,0.93,1.00};
  double[] y=new double[10];
  double[] t={0.0,0.33,0.67,0.95,1.05};
  double f,h,s;
  int i;
  for(i=0;i<10;i++)y[i]=Math.sin(x[i]);
  for(i=0;i<5;i++)
  {f=enlgr(x,y,t[i]);h=enlgr2(x,y,t[i]);s=Math.sin(t[i]);
   g.drawString("t="+t[i]+"   f(t)="+f+"   h(t)="+h+"  实际值="+s,10,20+20*i);}
 }
}