#! /usr/bin/env python3
#
def corkscrew_plot3d ( ):

#*****************************************************************************80
#
## predator_plot3d() computes and plots some predator/prey data.
#
#  Licensing:
#
#    This code is distributed under the MIT license.
#
#  Modified:
#
#    30 September 2026
#
#  Author:
#
#    John Burkardt
#
  import matplotlib
  import numpy as np
  import platform

  print ( '' )
  print ( 'predator_plot3d():' )
  print ( '  matplotlib version: ' + matplotlib.__version__ )
  print ( '  numpy version:      ' + np.version.version )
  print ( '  python version:     ' + platform.python_version ( ) )
  print ( '  Model the interaction between rabbits and foxes.' )

  header = 'predator'
#
#  Define the data.
#
  n = 1001

  t = np.zeros ( n )
  pred = np.zeros ( n )
  prey = np.zeros ( n )
#
#  Define the data.
#
  dt = ( 5.0 - 0.0 ) / ( n - 1 );

  t[0] = 0.0;
  prey[0] = 5000.0;
  pred[0] = 100.0;

  for i in range ( 1, n ):
    t[i] = t[i-1] + dt;
    prey[i] = prey[i-1] + dt * (    2.0 * prey[i-1] - 0.001 * pred[i-1] * prey[i-1] );
    pred[i] = pred[i-1] + dt * ( - 10.0 * pred[i-1] + 0.002 * pred[i-1] * prey[i-1] );
#
#  Create the data file.
#
  data_filename = header + '_data.txt'
  data_unit = open ( data_filename, 'wt' )
  for i in range ( 0, n ):
    s = ( '  %14.6g  %14.6g  %14.6g\n' % ( t[i], pred[i], prey[i] ) )
    data_unit.write ( s )
  data_unit.close ( )
  print ( '  Created data file "' + data_filename + '"' )
#
#  Create the command file.
#
  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 + '.png"\n' )
  command_unit.write ( 'set xlabel "Time"\n' )
  command_unit.write ( 'set ylabel "Predator"\n' )
  command_unit.write ( 'set zlabel "Prey"\n' )
  command_unit.write ( 'set title "Predator/prey evolution"\n' )
  command_unit.write ( 'set grid\n' )
  command_unit.write ( 'set timestamp\n' )
  command_unit.write ( 'set style data lines\n' )
  command_unit.write ( 'splot "' + data_filename + \
    '" using 1:2:3 with lines\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 ( )
  corkscrew_plot3d ( )
  timestamp ( )