说明：  拉格朗日插值也叫两点插值，已知函数y = f (x)在给定互异点x0, x1上的值为y0= f (x0)，y1=f (x1)线性插值就是构造一个一次多项式 　　P1(x) = ax + b 　　使它满足条件 　　P1 (x0) = y0 P1 (x1) = y1
(Lagrange interpolation, also known as two points interpolated known function y = f (x) given different point x0, the value y0 on x1 = f (x0), y1 = f (x1) linear interpolation is construct a polynomial P1 (x) = the AX PPLS b that it satisfy the condition P1 (X0) = Y0 P1 (x1) = Y1)