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

#*****************************************************************************80
#
## grid_line_contour() draws a contour line plot from a table Z(X,Y).
#
#  Discussion:
#
#    Here, the grid is a 41x41 array of equally spaced points in [-2,2]x[-2,2].
#
#      x = linspace ( -2.0, +2.0, 41 );
#      y = linspace ( -2.0, +2.0, 41 );
#      [ X, Y ] = meshgrid ( x, y );
#
#    and Z(X,Y) is a function which could be evaluated by:
#
#      Z = exp ( - ( X^2 + Y^2 ) ) ...
#       * cos ( 0.25 * X ) ...
#       * sin ( Y ) ...
#       * cos ( 2 * (X^2 + Y^2 ) );
#
#  Licensing:
#
#    This code is distributed under the MIT license.
#
#  Modified:
#
#    01 August 2020
#
#  Author:
#
#    John Burkardt
#
  import matplotlib.pyplot as plt
  import numpy as np
  import platform
  from matplotlib import cm

  print ( '' )
  print ( 'grid_line_contour():' )
  print ( '  Python version: %s' % ( platform.python_version ( ) ) )
  print ( '  Make a contour line plot Z(X,Y) for a 41x41 table.' )
#
#  Read the data from the file.
#
  x = []
  y = []
  z = []

  file = open ( 'grid_data.txt', 'r' )

  for line in file:
    line = line.strip ( )
    columns = line.split ( )
    x.append ( float ( columns[0] ) )
    y.append ( float ( columns[1] ) )
    z.append ( float ( columns[2] ) )

  file.close ( )
#
#  The data was stored as a vector.
#  Reshape it to 41x41 arrays.
#
  x = np.reshape ( x, ( 41, 41 ) )
  y = np.reshape ( y, ( 41, 41 ) )
  z = np.reshape ( z, ( 41, 41 ) )
#
#  Form the figure.
#
  levels = 15
  ax = plt.figure ( )
  plt.contour ( x, y, z, levels )
  plt.title ( 'Contour line plot of 41x41 table Z(X,Y)', fontsize = 16 )
  plt.xlabel ( '<--- X --->', fontsize = 16 )
  plt.ylabel ( '<--- Y --->', fontsize = 16 )
  filename = 'grid_line_contour.png'
  plt.savefig ( filename )
  print ( '' )
  print ( '  Graphics saved as "%s"' % ( filename ) )
  plt.show ( block = False )
  plt.close ( )
#
#  Terminate.
#
  print ( '' )
  print ( 'grid_line_contour():' )
  print ( '  Normal end of execution.' )
  return

def timestamp ( ):

#*****************************************************************************80
#
## timestamp() prints the date as a timestamp.
#
#  Licensing:
#
#    This code is distributed under the MIT license. 
#
#  Modified:
#
#    06 April 2013
#
#  Author:
#
#    John Burkardt
#
  import time

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

  return

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