old_contents: """
  ==================
  Colormap pitfalls.
  ==================
  
  Choosing the right colormap is important. A bad colormap like ``jet``
  (standard in ROOT and matplotlib < 2.0) fools you into seeing structure
  where there isn't any.
  """
  
  import numpy as np
  import matplotlib.pyplot as plt
  from mpl_toolkits.axes_grid1 import make_axes_locatable
  
  x = np.linspace(-np.pi, np.pi, 300)
  xx, yy = np.meshgrid(x, x)
  z = np.cos(xx) + np.cos(yy)
  
  fig, axes = plt.subplots(3, 1)
  
  for ax, colourmap in zip(axes, ['jet', 'gray', 'cubehelix']):
      ax.set_title(colourmap)
      im = ax.imshow(z, cmap=plt.get_cmap(colourmap))
      divider = make_axes_locatable(ax)
      cax = divider.append_axes('right', size='20%', pad=0.05)
      cbar = plt.colorbar(im, cax=cax)
  
new_contents: """
  ==================
  Colormap pitfalls.
  ==================
  
  Choosing the right colormap is important. A bad colormap like ``jet``
  (standard in ROOT and matplotlib < 2.0) fools you into seeing structure
  where there isn't any.
  """
  
  import numpy as np
  import matplotlib.pyplot as plt
  from mpl_toolkits.axes_grid1 import make_axes_locatable
  
  x = np.linspace(-np.pi, np.pi, 300)
  xx, yy = np.meshgrid(x, x)
  z = np.cos(xx) + np.cos(yy)
  
  fig, axes = plt.subplots(2, 2)
  
  for ax, colourmap in zip(axes, ['gray', 'jet', 'cubehelix', 'viridis']):
      ax.set_title(colourmap)
      im = ax.imshow(z, cmap=plt.get_cmap(colourmap))
      divider = make_axes_locatable(ax)
      cax = divider.append_axes('right', size='20%', pad=0.05)
      cbar = plt.colorbar(im, cax=cax)
  
subject: Add viridis colour map