from matplotlib import cm
import matplotlib.pyplot as plt
import numpy as np
import platform

print ( '' )
print ( 'contours():' )
print ( '  Use meshgrd to sample a .' )
#
#  Create the mesh vectors.
#
xvec = np.linspace ( -2.0, 2.0, 31 )
yvec = np.linspace ( -2.0, 2.0, 31 )
#
#  Create the mesh matrices.
#
X, Y = np.meshgrid ( xvec, yvec )
#
#  Evaluate the function at the mesh points.
#
Z = 2 * X**2 - 1.05 * X**4 + X**6 / 6 + X * Y + Y**2
#
#  Plot
#
plt.clf ( )

plt.contourf ( X, Y, Z, cmap = cm.Pastel1 )
plt.contour ( X, Y, Z, levels = 35 )
plt.axis ( 'equal' )
plt.title ( 'A contour plot', fontsize = 16 )
plt.xlabel ( '<--- X --->', fontsize = 16 )
plt.ylabel ( '<--- Y --->', fontsize = 16 )
filename = 'contours.png'
plt.savefig ( filename )
print ( '  Graphics saved as "%s"' % ( filename ) )
plt.show ( )
plt.close ( )