2 插值
拉格朗日插值
基函数 l k ( x ) = w n + 1 ( x ) ( x − x k ) w n + 1 ′ ( x k ) l_k(x)=\dfrac{w_{n+1}(x)}{(x-x_k)w_{n+1}'(x_k)} lk(x)=(x−xk)wn+1′(xk)wn+1(x)
拉格朗日插值多项式 L n ( x ) = ∑ k = 0 n y k l k ( x ) = ∑ k = 0 n y k w n + 1 ( x ) ( x − x k ) w n + 1 ′ ( x k ) \displaystyle{L_n(x)=\sum_{k=0}^{n}y_kl_k(x)=\sum_{k=0}^{n}y_k\frac{w_{n+1}(x)}{(x-x_k)w_{n+1}'(x_k)}} Ln(x)=k=0∑nyklk(x)=k=0∑nyk(x−xk)wn+1′(xk)wn+1(x)
插值余项 R n ( x ) = f ( n + 1 ) ( ξ ) ( n + 1 ) ! w n + 1 ( x ) R_n(x)=\dfrac{f^{(n+1)}(\xi)}{(n+1)!}w_{n+1}(x) Rn(x)=(n+1)!f(n+1)(ξ)wn+1