code: def knot_removal_alpha_j(u, degree, knotvector, num, idx):
      
      return (u - knotvector[idx - num]) / (knotvector[idx + degree + 1] - knotvector[idx - num])
docs: Computes :math:`\\alpha_{j}` coefficient for knot removal algorithm.
  
      Please refer to Eq. 5.29 of The NURBS Book by Piegl & Tiller, 2nd Edition, p.184 for details.
  
      :param u: knot
      :type u: float
      :param degree: degree
      :type degree: int
      :param knotvector: knot vector
      :type knotvector: tuple
      :param num: knot removal index
      :type num: int
      :param idx: iterator index
      :type idx: int
      :return: coefficient value
      :rtype: float