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d-Chebyshev Polynomial


The d-Chebyshev polynomials form the polynomial sequence {P_n(x)}_(n>=0) defined by

 P_n(x)=x^n,    0<=n<=d
(1)

and

 P_(n+d+1)(x)=xP_(n+d)(x)-gammaP_n(x),    n>=0,
(2)

where d is a positive integer and gamma!=0 is constant. They form a d-symmetric d-orthogonal polynomial sequence (Douak and Maroni 1997a, 1997b).

Their ordinary generating function is

 sum_(n=0)^inftyP_n(x)t^n=1/(1-xt+gammat^(d+1)),
(3)

and expansion in the canonical basis gives

 P_n(x)=sum_(k=0)^(|_n/(d+1)_|)(-gamma)^k(n-dk; k)x^(n-(d+1)k).
(4)

In particular, only powers congruent to n modulo d+1 occur. For d=1 and gamma=1/4,

 P_n(x)=2^(-n)U_n(x),
(5)

where U_n(x) is a Chebyshev polynomial of the second kind (Mesquita and da Rocha 2026). More generally, if n=(d+1)k+mu and mu>=1, then zero is a root of multiplicity mu; it is not a root when mu=0. For gamma=1/4, the other roots occur k at a time on each of the d+1 rays with arguments 2pij/(d+1), where j=0, 1, ..., d (Mesquita and da Rocha 2026).


See also

Chebyshev Polynomial of the Second Kind, d-Orthogonal Polynomial, Ordinary Generating Function

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References

Douak, K. and Maroni, P. "On d-Orthogonal Tchebychev Polynomials. I." Appl. Numer. Math. 24, 23-53, 1997a. https://doi.org/10.1016/S0168-9274(97)00006-8.Douak, K. and Maroni, P. "On d-Orthogonal Tchebychev Polynomials. II." Methods Appl. Anal. 4, 404-429, 1997b. https://doi.org/10.4310/MAA.1997.v4.n4.a3.Mesquita, T. A. and da Rocha, Z. "On Connection Coefficients of d-Orthogonal Polynomials in Terms of Orthogonal Polynomials and the Canonical Basis." Math. Comput. Sci. 20, #15, 2026. https://doi.org/10.1007/s11786-026-00631-x.

Cite this as:

Weisstein, Eric W. "d-Chebyshev Polynomial." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/d-ChebyshevPolynomial.html

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