Jacobi Polynomial Calculator

P_n^(α,β)(x) general family

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About Jacobi Polynomial Calculator

A Jacobi polynomial calculator computing P_n^(α,β)(x), the most general classical orthogonal polynomial on [-1,1] with weight (1−x)^α(1+x)^β. Legendre: α=β=0. Chebyshev T: α=β=−1/2. Gegenbauer: α=β. Client-side.

Jacobi Polynomial Calculator Features

  • P_n^(α,β)(x)
  • Special cases
  • Weight function
  • Recurrence
  • Sequence
Jacobi polynomials P_n^(α,β)(x): orthogonal on [-1,1] with weight (1−x)^α(1+x)^β. The 'mother' of all classical orthogonal polynomials on finite intervals. Special cases: Legendre (0,0), Chebyshev T (−½,−½), Chebyshev U (½,½), Gegenbauer (α=β).

How to Use

Enter n, α, β, x:

  • Value: P_n^(α,β)(x)
  • Presets: Known families
  • Sequence: n=0..N

Family Hierarchy

Jacobi(α,β) → Gegenbauer(α=β) → Legendre(0,0) & Chebyshev(−½,−½). Each specialization adds symmetry. Jacobi is the most general with TWO parameters controlling the weight at each endpoint.

Applications

  • Spectral methods with non-uniform weights
  • Random matrix theory (Jacobi ensemble)
  • Representation theory of SU(2)
  • Approximation theory on [-1,1]

Step-by-Step Instructions

  1. 1Enter n, α, β.
  2. 2Enter x.
  3. 3Compute value.
  4. 4Try presets.
  5. 5View sequence.

Jacobi Polynomial Calculator — Frequently Asked Questions

Why is Jacobi the 'mother' polynomial?+

The Bochner-Krall theorem: the only polynomial families orthogonal w.r.t. a weight on an interval AND satisfying a second-order ODE are Jacobi (finite interval), Laguerre (semi-infinite), and Hermite (full line). Jacobi subsumes ALL classical finite-interval cases.

What are Gegenbauer/ultraspherical polynomials?+

C_n^λ(x) = Jacobi with α=β=λ−½. These have the extra symmetry C_n^λ(-x)=(-1)^nC_n^λ(x). They appear in the addition theorem for spherical harmonics in d dimensions. Legendre = C_n^{1/2}, Chebyshev U = C_n^1.

What constraints on α and β?+

Need α,β > -1 for the weight to be integrable. Common choices: α,β ∈ {-½, 0, ½, 1}. Larger α,β concentrate the weight near the endpoints. α=β gives symmetric weight.

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