code: def knot_insertion_alpha(u, knotvector, span, idx, leg):
      
      return (u - knotvector[leg + idx]) / (knotvector[idx + span + 1] - knotvector[leg + idx])
docs: Computes :math:`\\alpha` coefficient for knot insertion algorithm.
  
      :param u: knot
      :type u: float
      :param knotvector: knot vector
      :type knotvector: tuple
      :param span: knot span
      :type span: int
      :param idx: index value (degree-dependent)
      :type idx: int
      :param leg: i-th leg of the control points polygon
      :type leg: int
      :return: coefficient value
      :rtype: float