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

  import matplotlib.pyplot as plt
  import numpy as np

  n = 101
  x1 = -12
  x2 = +12
  x = np.linspace ( x1, x2, n )
  y = np.sin ( x ) / x
#
#  Patch the data.
#
  y[x==0] = 1.0

  plt.clf ( )
  plt.plot ( x, y, 'g-', linewidth = 2 )
  plt.grid ( True )
  filename = 'sinc.png'
  plt.savefig ( filename )
  print ( '  Graphics saved as "' + filename + '"' )
  plt.show ( )
#
#  Now exhibit min, mean and max.
#
  ymin = np.min ( y )
  imin = np.argmin ( y )
  xmin = x[imin]

  print ( ymin, imin, xmin )

  ymean = np.mean ( y )

  ymax = np.max ( y )
  imax = np.argmax ( y )
  xmax = x[imax]

  print ( ymax, imax, xmax )

  plt.clf ( )
  plt.plot ( x, y, 'g-', linewidth = 2 )
  plt.plot ( [x1,x2], [ymax,ymax], 'b-' )
  plt.plot ( [xmax,xmax], [0.0,ymax], 'b-' )
  plt.plot ( [x1,x2], [ymin,ymin], 'r-' )
  plt.plot ( [xmin,xmin], [0.0,ymin], 'r-' )
  plt.plot ( [x1,x2], [ymean,ymean], 'c:', linewidth = 3 )
  plt.plot ( [x1,x2], [0.0,0.0], 'k-' )
  plt.grid ( True )
  filename = 'sinc_marked.png'
  plt.savefig ( filename )
  print ( '  Graphics saved as "' + filename + '"' )
  plt.show ( )
#
#  Now exhibit points with y<0
#
  plt.clf ( )
  plt.plot ( x, y, 'g-', linewidth = 2 )
  plt.plot ( x[y<0], y[y<0], 'r.', markersize = 10 )
  plt.plot ( [x1,x2], [0.0,0.0], 'k-' )
  plt.grid ( True )
  filename = 'sinc_negative.png'
  plt.savefig ( filename )
  print ( '  Graphics saved as "' + filename + '"' )
  plt.show ( )

  return

if ( __name__ == '__main__' ):
  minmax_plot ( )