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单词 AppellSequence
释义

Appell sequence


The sequenceMathworldPlanetmath of polynomialsPlanetmathPlanetmath

P0(x),P1(x),P2(x),(1)

with

Pn(x):=axn  (n=0, 1, 2,)

is a geometric sequence and has trivially the properties

Pn(x)=nPn-1(x)  (n=0, 1, 2,)(2)

and

Pn(x+y)=k=0n(nk)Pk(x)yn-k(3)

(see the binomial theorem).  There are also other polynomial sequences (1) having these properties, for example the sequences of the Bernoulli polynomialsDlmfDlmfMathworldPlanetmathPlanetmath, the Euler polynomialsDlmfDlmfMathworldPlanetmath and the Hermite polynomialsDlmfDlmfDlmfMathworldPlanetmath.  Such sequences are called Appell sequences and their members are sometimes characterised as generalised monomialsPlanetmathPlanetmath, because of resemblance to the geometric sequence.

Given the first member P0(x), which must be a nonzero constant polynomial, of any Appell sequence (1), the other members are determined recursively by

Pn(x)=0xPn-1(t)𝑑t+Cn(4)

as one gives the values of the constants of integration Cn; thus the number sequence

C0,C1,C2,

determines the Appell sequence uniquely.  So the choice  C1=C2=:=0  yields a geometric sequence and the choice  Cn:=Bn  for  n=0, 1, 2,  the Bernoulli polynomials (http://planetmath.org/BernoulliPolynomialsAndNumbers).

The properties (2) and (3) areequivalentMathworldPlanetmathPlanetmathPlanetmathPlanetmath (http://planetmath.org/Equivalent3).  The implicationMathworldPlanetmath(2)(3) may be shown byinductionMathworldPlanetmath (http://planetmath.org/Induction) on n.  The reverseimplication is gotten by using the definition of derivativePlanetmathPlanetmath:

Pn(x)=limΔx0Pn(x+Δx)-Pn(x)Δx
=limΔx0P0(x)Δxn+(n1)P1(x)Δxn-1++(nn-1)Pn-1(x)ΔxΔx
=(nn-1)Pn-1(x)
=nPn-1(x).

See also http://en.wikipedia.org/wiki/Appell_polynomialsWiki.

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更新时间:2025/5/4 20:20:38