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

using namespace std;

int main ( );
void timestamp ( );

/******************************************************************************/

int main ( )

/******************************************************************************/
//
//  Purpose:
//
//    grid_surface() draws a surface from a table Z(X,Y).
//
//  Licensing:
//
//    This code is distributed under the MIT license.
//
//  Modified:
//
//    26 September 2026
//
//  Author:
//
//    John Burkardt
//
{
  string command_filename = "grid_commands.txt";
  ofstream command;
  string data_filename = "grid_data.txt";
  ofstream data;
  string plot_filename = "grid_surface.png";
  int i;
  int j;
  int m;
  int n;
  double r2;
  double x;
  double y;
  double z;

  timestamp ( );
  cout << "\n";
  cout << "grid_surface():\n";
  cout << "  C++ version\n";
  cout << "  Make a surface plot Z(X,Y) for a 41x41 table.\n";
//
//  Set number of points in plot.
//
  m = 41;
  n = 41;
//
//  Define the data.
//
  data.open ( data_filename.c_str ( ) );

  for ( i = 0; i < m; i++ )
  {
    if ( 0 < i )
    {
      data << "\n";
    }
    x = ( ( m - i - 1 ) * ( -2.0 ) 
        + (     i     ) * (  2.0 ) ) 
        / ( m     - 1 );
    for ( j = 0; j < n; j++ )
    {
      y = ( ( n - j - 1 ) * ( -2.0 ) 
          + (     j     ) * (  2.0 ) )
          / ( n     - 1 );
      r2 = x * x + y * y;
      z = exp ( - r2 ) * cos ( 0.25 * x ) * sin ( y ) * cos ( 2 * r2 );
      data << "  " << x
           << "  " << y
           << "  " << z << "\n";
    }
  }

  data.close ( );

  cout << "\n";
  cout << "  Data stored in '" << data_filename << "'.\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 zlabel 'Z'\n";
  command << "set title 'Grid surface'\n";
  command << "set view 77, 77\n";
  command << "set xyplane -0.5\n";
  command << "set hidden3d\n";
  command << "set grid\n";
  command << "set timestamp\n";
  command << "set style data lines\n";
  command << "splot '" << data_filename << "' with lines\n";
  command << "quit\n";

  command.close ( );

  cout << "  plot commands stored in '" << command_filename << "'.\n";
//
//  Terminate.
//
  cout << "\n";
  cout << "grid_surface():\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:
//
//    08 July 2009
//
//  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
}