example4_2.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 Example4_2 extends Applet
{public static double  f(double x)
 {double y;
  y=x*x*(x*x-4)+4;
  //y=x*x*(x+4)-10;
  return y;
 }
 public static double Df(double x)
 {double y;
  //y=(3*x+8)*x;
  y=x*(4*x*x-8);
  return y;
 }
 public static double D2f(double x)
 {double y;
  y=12*x*x-8;
  //y=6*x+8;
  return y;
	 }

public static double newton(double x,double eps)
{double x1=x,x2=0,d0,d1,d2;
 while(Math.abs(x2-x1)>eps)
 {x2=x1;d0=f(x1);d1=Df(x1);
  if(Math.abs(d0)<eps)break;
  if(Math.abs(d1)<eps){d2=D2f(x1);x1=x1-d0*d1/(d1*d1-d0*d2);}
  else x1=x1-d0/d1;
 }
 return x1;
}
public void paint(Graphics g)
{double x,eps=1e-7;
 x=newton(1.5,eps);
 g.drawString("在1.5附近的根为："+x,10,20);
}

}