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

using namespace std;

int main ( );
void timestamp ( );

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

int main ( )

//****************************************************************************80
//
//  Purpose:
//
//    least_squares_plots() compares data, a formula, and a least squares approximation.
//
//  Licensing:
//
//    This code is distributed under the MIT license.
//
//  Modified:
//
//    29 September 2026
//
//  Author:
//
//    John Burkardt
//
{
  string command_filename = "least_squares_commands.txt";
  ofstream command;
  string data1_filename = "least_squares1_data.txt";
  string data2_filename = "least_squares2_data.txt";
  string data3_filename = "least_squares3_data.txt";
  string plot_filename = "least_squares_plots.png";

  timestamp ( );
  cout << "\n";
  cout << "least_squares_plots():\n";
  cout << "  C++ version\n";
  cout << "  On a single picture, plot:\n";
  cout << "  * 15 data points (X,Y).\n";
  cout << "  * the least squares line Y=A*X+B.\n";
  cout << "  * the exact formula Y=1/2*X^2 + 1.\n";
//
//  Create the command file.
//
  command.open ( command_filename.c_str ( ) );

  command << "# " << command_filename << "\n";
  command << "#\n";
  command << "# Usage:\n";
  command << "#  gnuplot < " << command_filename << "\n";
  command << "#\n";
  command << "set term png\n";
  command << "set output '" << plot_filename << "'\n";
  command << "set xlabel '<--- X --->'\n";
  command << "set ylabel '<--- Y --->'\n";
  command << "set title 'Formula (green), Data (blue), least squares fit (red)'\n";
  command << "set grid\n";
  command << "set timestamp\n";
  command << "set key on\n";

  command << "plot '" << data1_filename 
    << "' using 1:2 with points lw 3 lt rgb 'blue' title 'Data', \\\n";
  command << "      '" << data2_filename 
    << "' using 1:2 with lines lw 3 lt rgb 'red' title 'Least Squares Line', \\\n";
  command << "      '" << data3_filename 
    << "' using 1:2 with lines lw 3 lt rgb 'green' title 'Exact Formula'\n";

  command << "quit\n";

  command.close ( );
//
//  Terminate.
//
  cout << "\n";
  cout << "least_squares_plots():\n";
  cout << "  Normal end of execution.\n";
  cout << "\n";
  timestamp ( );

  return 0;
}
//****************************************************************************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 MIT license. 
//
//  Modified:
//
//    19 March 2018
//
//  Author:
//
//    John Burkardt
//
{
# define TIME_SIZE 40

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

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

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

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

  return;
# undef TIME_SIZE
}