说明：  寻找三次样条多项式需要求解大量的线性方程。实际上，给定N个断点，就要寻找N-1个三次多项式，每个多项式有4个未知系数。这样，所求解的方程组包含有4*(N-1)个未知数。把每个三次多项式列成特殊形式，并且运用各种约束，通过求解N个具有N个未知系数的方程组，就能确定三次多项式。
(find cubic spline solving polynomial need a lot of linear equations. In fact, given N breakpoints, it is necessary to look for N-1 cubic polynomial, each with four polynomial coefficients unknown. Thus, by solving the equations contain 4* (N-1) unknown. Each cubic polynomial Timing special form, and use of various constraints, by solving N with N unknown coefficient equations, we can identify three polynomial.)