# include <cstdlib>
# include <iostream>
# include <iomanip>
# include <cmath>
# include <ctime>

# include "llsq.hpp"

using namespace std;

//****************************************************************************80

void llsq ( int n, double x[], double y[], double &a, double &b )

//****************************************************************************80
//
//  Purpose:
//
//    LLSQ solves a linear least squares problem matching a line to data.
//
//  Discussion:
//
//    A formula for a line of the form Y = A * X + B is sought, which
//    will minimize the root-mean-square error to N data points ( X[I], Y[I] );
//
//  Licensing:
//
//    This code is distributed under the GNU LGPL license. 
//
//  Modified:
//
//    17 July 2011
//
//  Author:
//
//    John Burkardt
//
//  Parameters:
//
//    Input, int N, the number of data values.
//
//    Input, double X[N], Y[N], the coordinates of the data points.
//
//    Output, double &A, &B, the slope and Y-intercept of the least-squares
//    approximant to the data.
//
{
  double bot;
  int i;
  double top;
  double xbar;
  double ybar;
//
//  Special case.
//
  if ( n == 1 )
  {
    a = 0.0;
    b = y[0];
    return;
  }
//
//  Average X and Y.
//
  xbar = 0.0;
  ybar = 0.0;
  for ( i = 0; i < n; i++ )
  {
    xbar = xbar + x[i];
    ybar = ybar + y[i];
  }
  xbar = xbar / ( double ) n;
  ybar = ybar / ( double ) n;
//
//  Compute Beta.
//
  top = 0.0;
  bot = 0.0;
  for ( i = 0; i < n; i++ )
  {
    top = top + ( x[i] - xbar ) * ( y[i] - ybar );
    bot = bot + ( x[i] - xbar ) * ( x[i] - xbar );
  }
  a = top / bot;

  b = ybar - a * xbar;

  return;
}
//****************************************************************************80

void timestamp ( )

//****************************************************************************80
//
//  Purpose:
//
//    TIMESTAMP prints the current YMDHMS date as a time stamp.
//
//  Example:
//
//    31 May 2001 09:45:54 AM
//
//  Licensing:
//
//    This code is distributed under the GNU LGPL license. 
//
//  Modified:
//
//    08 July 2009
//
//  Author:
//
//    John Burkardt
//
//  Parameters:
//
//    None
//
{
# define TIME_SIZE 40

  static char time_buffer[TIME_SIZE];
  const struct std::tm *tm_ptr;
  size_t len;
  std::time_t now;

  now = std::time ( NULL );
  tm_ptr = std::localtime ( &now );

  len = std::strftime ( time_buffer, TIME_SIZE, "%d %B %Y %I:%M:%S %p", tm_ptr );

  std::cout << time_buffer << "\n";

  return;
# undef TIME_SIZE
}