#! /usr/bin/env python3
#
def collatz_dot_plot ( nmax ):
#
#  Evaluate T(n) for n = 1 through NMAX and plot the results.
#
  from collatz import collatz
  import matplotlib.pyplot as plt
#
#  Store n and T(n) in lists.
#
  nvec = []
  tvec = []
  for n in range ( 1, nmax + 1 ):
    nvec.append ( n )
    tn = collatz ( n )
    tvec.append ( tn )

  plt.clf ( )
  plt.plot ( nvec, tvec, 'bo' )
  plt.plot ( nvec, nvec, 'r-' )
  plt.xlabel ( '<-- n -->' )
  plt.ylabel ( '<-- T(n) --.' )
  filename = 'collatz_dot_plot.png'
  plt.savefig ( filename )
  print ( '  Graphics saved as "' + filename + '"' )
  plt.show ( )
  plt.close ( )

  return

if ( __name__ == '__main__' ):
  collatz_dot_plot ( 50 )