example3_13.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 Example3_13 extends Applet
{ public static void grad(double[][] a,double[] b,double[] x,double eps)
  {int i,j,k,n=b.length;
   double[] p=new double[n];
   double[] r=new double[n];
   double[] ap=new double[n];
   double temp1,temp2,alpha;
   for(i=0;i<n;i++)
    {r[i]=b[i];
     for(j=0;j<n;j++)
     r[i]-=a[i][j]*x[j];}
  for(i=0;i<n;i++)p[i]=r[i];
  temp2=0;
   for(i=0;i<n;i++)
   {temp2+=r[i]*r[i];}
  for(k=0;k<n;k++)
  {if(temp2<eps*eps)break;
   alpha=temp1=temp2;
   for(i=0;i<n;i++)
   { ap[i]=0;
     for(j=0;j<n;j++)
     ap[i]+=a[i][j]*p[j];
   }
   temp2=0;
   for(i=0;i<n;i++)temp2+=ap[i]*p[i];
   alpha/=temp2;
   for(i=0;i<n;i++)
     {x[i]+=alpha*p[i];
      r[i]-=alpha*ap[i];}
    temp2=0;
    for(i=0;i<n;i++)temp2+=r[i]*r[i];
    temp1=temp2/temp1;
    for(i=0;i<n;i++)p[i]=r[i]+temp1*p[i];
   }

    }

 public void paint(Graphics g)
 {double[][] a={{5,7,6,5},{7,10,8,7},{6,8,10,9},{5,7,9,10}};
  double[] b={1,2,3,4};
  double[] x={0,0,0,0};
  double eps=1e-7;
  grad(a,b,x,eps);
  for(int i=0;i<x.length;i++)
    g.drawString("X"+i+"="+x[i],10,20*i+20);
 }

}