text: # backend_demo
  
  import numpy as np
  import matplotlib
  # matplotlib.use('PDF')
  import matplotlib.pyplot as plt
  
  f = lambda x: 1/((x-3)**2+.01) + 1/((x-9)**2+.04) - 6
  xvalues = np.linspace(2, 10, 300)
  yvalues = f(xvalues)
  
  plt.plot(xvalues, yvalues)
  plt.xlabel('$x$')
  plt.ylabel('$f(x)$')
  plt.title('The "humps" function')
  
  plt.show()
  
  print('Done plotting.')
  