Difference between revisions of "Chebyshev T"
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[[T_(n+1)(x)-2xT_n(x)+T_(n-1)(x)=0]]<br /> | [[T_(n+1)(x)-2xT_n(x)+T_(n-1)(x)=0]]<br /> | ||
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{{:Relationship between Chebyshev T and hypergeometric 2F1}} | {{:Relationship between Chebyshev T and hypergeometric 2F1}} | ||
Revision as of 22:15, 19 December 2017
Chebyshev polynomials of the first kind are orthogonal polynomials defined for $n=0,1,2,\ldots$ by $$T_n(x) = \cos(n \mathrm{arccos}(x)),$$ where $\cos$ denotes cosine and $\mathrm{arccos}$ denotes arccos.
Properties
T_(n+1)(x)-2xT_n(x)+T_(n-1)(x)=0
Orthogonality of Chebyshev T on (-1,1)
Theorem
The following formula holds for $n \in \{0,1,2,\ldots\}$: $$T_n(x) = {}_2F_1 \left( -n,n ; \dfrac{1}{2}; \dfrac{1-x}{2} \right),$$ where $T_n$ denotes a Chebyshev polynomial of the first kind and ${}_2F_1$ denotes the hypergeometric pFq.
Proof
References
Theorem
The following formula holds for $n \in \{1,2,3,\ldots\}$: $$T_n(x)=\dfrac{n}{2} \displaystyle\lim_{\lambda \rightarrow 0} \dfrac{C_n^{\lambda}(x)}{\lambda},$$ where $T_n$ denotes a Chebyshev polynomial of the first kind and $C_n^{\lambda}$ denotes a Gegenbauer C polynomial.
