code: def vline_score(self, x, ymin, ymax):
          
          return self._vline_score[x, ymin, ymax]
docs: Returns the number of unbroken paths of qubits
  
          >>> [(x,y,1,k) for y in range(ymin,ymax+1)]
  
          for :math:`k = 0,1,\cdots,L-1`.  This is precomputed for speed.