#! /usr/bin/env python3
#
def damped_sine_plot ( ):

#*****************************************************************************80
#
## damped_sine_plot() plots the damped sine correlation function.
#
#  Licensing:
#
#    This code is distributed under the MIT license.
#
#  Modified:
#
#    23 September 2026
#
#  Author:
#
#    John Burkardt
#
  import matplotlib
  import numpy as np
  import platform

  print ( '' )
  print ( 'damped_sine_plot():' )
  print ( '  matplotlib version: ' + matplotlib.__version__ )
  print ( '  numpy version:      ' + np.version.version )
  print ( '  python version:     ' + platform.python_version ( ) )
  print ( '  damped_sine_plot() plots the damped sine correlation function.' )
#
#  Define the damped_sine data.
#
  rho0 = 1.0
  n = 101
  rho = np.linspace ( -12.0, +12.0, n )
  c = np.ones ( n )
  i = np.where ( rho != 0.0 )
  c[i] = rho0 * np.sin ( np.abs ( rho[i] ) / rho0 ) / np.abs ( rho[i] )
#
#  Request a plot.
#
  correlation_plot ( n, rho, c, 'damped_sine', 'Damped sine correlation' )

  return

def correlation_plot ( n, rho, c, header, title ):

#*****************************************************************************80
#
## correlation_plot() makes a plot of a correlation function.
#
#  Licensing:
#
#    This code is distributed under the MIT license.
#
#  Modified:
#
#    04 January 2013
#
#  Author:
#
#    John Burkardt
#
#  Input:
#
#    integer N, the number of arguments.
#
#    real RHO(N), the arguments.
#
#    real C(N), the correlations.
#
#    string HEADER, an identifier for the files.
#
#    string TITLE, a title for the plot.
#
  data_filename = header + '_data.txt'
  data_unit = open ( data_filename, 'wt' )
  for i in range ( 0, n ):
    s = ( '  %14.6g  %14.6g\n' % ( rho[i], c[i] ) )
    data_unit.write ( s )
  data_unit.close ( )
  print ( '  Created data file "' + data_filename + '"' )

  command_filename = header + '_commands.txt'
  command_unit = open ( command_filename, 'wt' )
  command_unit.write ( '# ' + command_filename + '\n' )
  command_unit.write ( '#\n' )
  command_unit.write ( '# Usage:\n' )
  command_unit.write ( '#  gnuplot < ' + command_filename + '\n' )
  command_unit.write ( '#\n' )
  command_unit.write ( 'set term png\n' )
  command_unit.write ( 'set output "' + header + '_plot.png"\n' )
  command_unit.write ( 'set xlabel "Distance Rho"\n' )
  command_unit.write ( 'set ylabel "Correlation C(Rho)"\n' )
  command_unit.write ( 'set title "' + title + '"\n' )
  command_unit.write ( 'set grid\n' )
  command_unit.write ( 'set timestamp\n' )
  command_unit.write ( 'set style data lines\n' )
  command_unit.write ( 'plot "' + data_filename + \
    '" using 1:2 lw 3 linecolor rgb "blue"\n' )
  command_unit.write ( 'quit\n' )
  command_unit.close ( )
  print ( '  Created command file "' + command_filename + '"' )

  return

def timestamp ( ):

#*****************************************************************************80
#
## timestamp() prints the date as a timestamp.
#
#  Licensing:
#
#    This code is distributed under the MIT license. 
#
#  Modified:
#
#    21 August 2019
#
#  Author:
#
#    John Burkardt
#
  import time

  t = time.time ( )
  print ( time.ctime ( t ) )

  return

if ( __name__ == '__main__' ):
  timestamp ( )
  damped_sine_plot ( )
  timestamp ( )