example2_2.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 Example2_2 extends Applet
{
  public static void  Mrinv(double[][] a,int n)
  {int i,j,row,col,k;
   double max,temp;
   int[] p=new int[n];
   double[][] b=new double[n][n];
   for(i=0;i<n;i++){p[i]=i;b[i][i]=1;}
   for(k=0;k<n;k++)
   {//找主元
    max=0;row=col=i;
    for(i=k;i<n;i++)
     for(j=k;j<n;j++)
     {temp=Math.abs(b[i][j]);
      if(max<temp){max=temp;row=i;col=j;}
	  }
	//交换行列，将主元调整到k行k列上
	if(row!=k)
	{for(j=0;j<n;j++)
	 {temp=a[row][j];a[row][j]=a[k][j];a[k][j]=temp;
	  temp=b[row][j];b[row][j]=b[k][j];b[k][j]=temp;}
	 }
	 if(col!=k)
	 {for(i=0;i<n;i++)
	   {temp=a[i][col];a[i][col]=a[i][k];a[i][k]=temp;}
	  j=p[col];p[col]=p[k];p[k]=j;
	 }
	 //处理
	 for(j=k+1;j<n;j++)a[k][j]/=a[k][k];
	 for(j=0;j<n;j++)b[k][j]/=a[k][k];
	 a[k][k]=1;
	 for(j=k+1;j<n;j++)
	 {for(i=0;i<k;i++)a[i][j]-=a[i][k]*a[k][j];
	  for(i=k+1;i<n;i++)a[i][j]-=a[i][k]*a[k][j];}
	 for(j=0;j<n;j++)
	 {for(i=0;i<k;i++)b[i][j]-=a[i][k]*b[k][j];
	  for(i=k+1;i<n;i++)b[i][j]-=a[i][k]*b[k][j];}
	  for(i=0;i<k;i++)a[i][k]=0;
	  a[k][k]=1;
  }
 //恢复行列次序；
 for(j=0;j<n;j++)
  {for(i=0;i<n;i++)a[p[i]][j]=b[i][j];}

 }

public void Mrcheng(double[][] a,double[][] b,double[][]c,int m,int n,int l)
  {double[][] d=new double[m][l];
   int i,j,k;
   for(i=0;i<m;i++)
     for(j=0;j<l;j++)
      {d[i][j]=0;
       for(k=0;k<n;k++)d[i][j]+=a[i][k]*b[k][j];}
  for(i=0;i<m;i++)
   for(j=0;j<l;j++)
    c[i][j]=d[i][j];
}

public void paint(Graphics g)
{double[][] a={{0.2368,0.2471,0.2568,1.2671},{1.1161,0.1254,0.1397,0.149},
               {0.1582,1.1675,0.1768,0.1871},{0.1968,0.2071,1.2168,0.2271}};
 double[][] b=new double[4][4];
 int i,j;
 for(i=0;i<4;i++)
  for(j=0;j<4;j++)
   b[i][j]=a[i][j];
 g.drawString("A=",10,20);
 for(i=0;i<4;i++)
 g.drawString(""+a[i][0]+"  "+a[i][1]+"  "+a[i][2]+"  "+a[i][3],10,40+20*i);
 Mrinv(a,4);
 g.drawString("A的逆阵B为",10,120);
 for(i=0;i<4;i++)
 g.drawString(""+a[i][0]+"  "+a[i][1]+"  "+a[i][2]+"  "+a[i][3],10,140+20*i);
 Mrcheng(a,b,a,4,4,4);
 for(i=0;i<4;i++)
  {for(j=0;j<4;j++)
   if(Math.abs(a[i][j])<1e-10)a[i][j]=0;
   if(Math.abs(a[i][i]-1)<1e-10)a[i][i]=1;}
 g.drawString("A*B=",10,220);
 for(i=0;i<4;i++)
 g.drawString(""+a[i][0]+"  "+a[i][1]+"  "+a[i][2]+"  "+a[i][3],10,240+20*i);
 }
}