チェビシェフ多項式の直交性
チェビシェフ多項式の直交性
(1)
\[ \int_{-1}^{1}T_{m}(x)T_{n}(x)\frac{dx}{\sqrt{1-x^{2}}}=\frac{\pi}{2}\left(\delta_{mn}+\delta_{0m}\delta_{0n}\right) \](2)
\[ \int_{-1}^{1}U_{m}(x)U_{n}(x)\sqrt{1-x^{2}}dx=\frac{\pi}{2}\delta_{mn} \](1)
\begin{align*} \int_{-1}^{1}T_{m}(x)T_{n}(x)\frac{dx}{\sqrt{1-x^{2}}} & =\int_{\pi}^{0}T_{m}(\cos t)T_{n}(\cos t)\frac{-\sin tdt}{\sin t}\qquad,\qquad x=\cos t\\ & =\int_{0}^{\pi}\cos\left(mt\right)\cos\left(nt\right)dt\\ & =\frac{1}{2}\int_{0}^{\pi}\left\{ \cos\left((m+n)t\right)+\cos\left((m-n)t\right)\right\} dt\\ & =\frac{1}{2}\left(\pi\delta_{0m}\delta_{0n}+\pi\delta_{mn}\right)\\ & =\frac{\pi}{2}\left(\delta_{0m}\delta_{0n}+\delta_{mn}\right) \end{align*}(2)
\begin{align*} \int_{-1}^{1}U_{m}(x)U_{n}(x)\sqrt{1-x^{2}}dx & =-\int_{\pi}^{0}U_{m}(\cos t)U_{n}(\cos t)\sin t\sin tdt\\ & =\int_{0}^{\pi}\sin\left((m+1)t\right)\sin\left((n+1)t\right)dt\\ & =-\frac{1}{2}\int_{0}^{\pi}\left\{ \cos\left((m+n+2)t\right)-\cos\left((m-n)t\right)\right\} dt\\ & =\frac{1}{2}\int_{0}^{\pi}\cos\left((m-n)t\right)dt\\ & =\frac{\pi}{2}\delta_{mn} \end{align*}ページ情報
タイトル | チェビシェフ多項式の直交性 |
URL | https://www.nomuramath.com/s03x0dst/ |
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チェビシェフ多項式の別表記
\[
T_{n}(x)=\frac{1}{2}\left(\left(x+i\sqrt{1-x^{2}}\right)^{n}+\left(x-i\sqrt{1-x^{2}}\right)^{n}\right)
\]
チェビシェフ多項式の級数表示
\[
T_{n}(x)=\sum_{k=0}^{\left\lfloor \frac{n}{2}\right\rfloor }\left(C(n,2k)\left(-1\right)^{k}\left(1-x^{2}\right)^{k}x^{n-2k}\right)
\]
第3種・第4種チェビシェフ多項式の漸化式
\[
V_{k+1}(x)=2xV_{k}(x)-V_{k-1}(x)
\]
(*)チェビシェフ多項式の超幾何表示
\[
T_{n}(x)=F\left(-n,n;\frac{1}{2};\frac{1-x}{2}\right)
\]