code: def cell_to_cellpar(cell):
      
      va, vb, vc = cell
      a = np.linalg.norm(va)
      b = np.linalg.norm(vb)
      c = np.linalg.norm(vc)
      alpha = 180.0/pi*arccos(dot(vb, vc)/(b*c))
      beta  = 180.0/pi*arccos(dot(vc, va)/(c*a))
      gamma = 180.0/pi*arccos(dot(va, vb)/(a*b))
      return np.array([a, b, c, alpha, beta, gamma])
docs: Returns the cell parameters [a, b, c, alpha, beta, gamma] as a
      numpy array.