// time_crout.java 

public class time_crout
{

  int N = 4096;
  double A[] = new double[N*N]; // destroyed
  double AA[] = new double[N*N]; // for checking
  double X[] = new double[N];
  double X_soln[] = new double[N];
  double Y[] = new double[N];
  double YY[] = new double[N];

  void init_matrix(int n)
  {
    double sum;

    for(int i=0; i<n; i++)
    {
      X_soln[i] = Math.random();
      for(int j=0; j<n; j++)
      {
        A[i*n+j] = Math.random();
        AA[i*n+j] = A[i*n+j];
      } // j
    } // i
    for(int i=0; i<n; i++)
    {
      sum = 0.0;
      for(int j=0; j<n; j++)
        sum = sum + A[i*n+j]*X_soln[j];
      Y[i] = sum;
      YY[i] = Y[i];
    } // i
    
    if(n<5)
    {
      for(int i=0; i<n; i++)
      {
        for(int j=0; j<n; j++)
	  System.out.println("A["+i+"]["+j+"]="+A[i*n+j]);
        System.out.println("X_soln["+i+"]="+X_soln[i]+", Y["+i+"]="+Y[i]);
        System.out.println(" ");
      } // i
    }
  } // end init_matrix

  time_crout()
  {
    double sum, sumerr, maxerr;
    double start, now, next;
  
    System.out.println("time_crout.java running");
    start  = System.currentTimeMillis()/1000.0;
    for(int n=4; n<N; n=n*2)
    {
      init_matrix(n);
      now  = System.currentTimeMillis()/1000.0;
      System.out.println("matrix initialized in "+(now-start)+" seconds");
      new crout1(n, A, Y, X);
      next  = System.currentTimeMillis()/1000.0;
      sumerr = 0.0;
      maxerr = 0.0;
      for(int i=0; i<n; i++)
      {
        sum = 0.0;
        for(int j=0; j<n; j++) sum = sum + AA[i*n+j]*X[j];
        sumerr = sumerr + Math.abs(sum-YY[i]);
        maxerr = Math.max(maxerr, Math.abs(X_soln[i]-X[i]));
        if(n<5) System.out.println("X["+i+"]="+X[i]+", err="+
                                   (X_soln[i]-X[i]));
      } // i
      System.out.println("n="+n+", sumerr="+sumerr+", maxerr="+maxerr);
      System.out.println("crout took "+(next-now)+" seconds");
    } // n
  } // end time_crout

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