code: def distance(a, b):
      
      [a_tonnetz, b_tonnetz] = [_to_tonnetz(x) for x in [a, b]]
      return np.linalg.norm(b_tonnetz - a_tonnetz)
docs: Compute tonnetz-distance between two chromagrams.
      
      ----
      >>> C = np.zeros(12)
      >>> C[0] = 1
      >>> D = np.zeros(12)
      >>> D[2] = 1
      >>> G = np.zeros(12)
      >>> G[7] = 1
  
      The distance is zero on equivalent chords
      >>> distance(C, C) == 0
      True
  
      The distance is symetric
      >>> distance(C, D) == distance(D, C)
      True
  
      >>> distance(C, D) > 0
      True
      >>> distance(C, G) < distance(C, D)
      True