docs: def stack_colormap(lower, upper, n=256):
      """
      Stacks two colormaps (``lower`` and ``upper``) such that
      low half -> ``lower`` colors, high half -> ``upper`` colors
  
      Args:
  
      	lower (colormap): colormap for the lower half of the stacked colormap.
  
      	upper (colormap): colormap for the upper half of the stacked colormap.
  
      	n (int): Number of colormap steps. Default is ``256``.
      """
      A = get_cmap(lower)
      B = get_cmap(upper)
      name = "%s-%s" % (A.name, B.name)
      lin = np.linspace(0, 1, n)
      return array_cmap(np.vstack((A(lin), B(lin))), name, n=n)