example2_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 Example2_8 extends Applet
{  public static boolean cholesky(double[][] a,int n)
  { int i,j,k;
    for(j=0;j<n;j++)
    { //计算l[j][j]
     for(k=0;k<j;k++)a[j][j]-=a[j][k]*a[j][k];
     if(a[j][j]<=0)return false;
     a[j][j]=Math.sqrt(a[j][j]);
    //计算l[i][j]
    for(i=j+1;i<n;i++)
     {for(k=0;k<j;k++)a[i][j]-=a[i][k]*a[j][k];
      a[i][j]/=a[j][j];}
    }
    return true;
  }

  public void paint(Graphics g)
  {double[][] a={{5,7,6,5},{7,10,8,7},{6,8,10,9},{5,7,9,10}};
   double det=1;
   if(cholesky(a,4))
   {g.drawString(""+a[0][0],10,20);
    g.drawString(""+a[1][0]+"  "+a[1][1],10,40);
    g.drawString(""+a[2][0]+"  "+a[2][1]+"  "+a[2][2],10,60);
    g.drawString(""+a[3][0]+"  "+a[3][1]+"  "+a[3][2]+"  "+a[3][3],10,80);
    for(int i=0;i<4;i++)det*=a[i][i];
    det*=det;
    g.drawString("Det="+det,10,100);}
   else g.drawString("矩阵不是正定阵",10,20);
  }

}