采用拟三对角矩阵反算出过一定点（大于等于3个）的控制顶点，再由这些控制顶点计算出3次B样条曲线，由于曲线封闭的，所以无需引入边界条件即可求得曲线。-Used to be anti-tridiagonal matrix calculated over a certain point (greater than or equal to 3) of the control points and then calculate the contr