// test_inverse.java  tough matrix to invert accurately 

public class test_inverse
{
  public test_inverse()
  {
    int n;
    double err;

    System.out.println("test_inverse.java on tough matrix to invert");
    n = 1;
    while(n < 256)
    {
      n=n*2;
      System.out.println("initializing big matrix, n="+n+", n*n="+(n*n));
      double AA[][] = new double[n][n];
      double AI[][] = new double[n][n];
      double II[][] = new double[n][n];

      for(int i=0; i<n; i++)
      {
        for(int j=0; j<n; j++)
        {
          AA[i][j] = 1.0/(double)((i+1)+(j+1));
        }
      }
      if(n<=4)
      {
        System.out.println("data");
        for(int i=0; i<n; i++)
        {
          for(int j=0; j<n; j++)
          {
            System.out.println("AA["+i+"]["+j+"]="+AA[i][j]);
          }
        }
      } 
      new inverse(AA, AI);
      if(n<=4)
      {
        System.out.println("inverse");
        for(int i=0; i<n; i++)
        {
          for(int j=0; j<n; j++)
          {
            System.out.println("AI["+i+"]["+j+"]="+AI[i][j]);
          }
        }
      } 
      err = 0.0;
      for(int i=0; i<n; i++)
      {
        for(int j=0; j<n; j++)
        {
          II[i][j] = 0.0;
          for(int k=0; k<n; k++)
	  {
            II[i][j] = II[i][j] + AA[i][k]*AI[k][j];
          }
          if(i == j)
            err = err + Math.abs(II[i][j]-1.0);
          else
            err = err + Math.abs(II[i][j]);
        }
      }
      System.out.println("AI["+n+"]["+n+"]="+AI[n-1][n-1]);
      System.out.println("sum of error="+err+
                         ", avg error="+(err/(double)(n*n)));
    }
    System.out.println("finished test_inverse.java");
  } // end test_inverse

  public static void main (String[] args)
  {
    new test_inverse();
  } // end main of test_inverse.java
} // end class test_inverse