Difference between revisions of "Jacobi P"

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The Jacobi polynomial $P_n^{(\alpha,\beta)}$ are [[orthogonal polynomials]] defined to be coefficient of $t^n$ in the expansion of
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The Jacobi polynomial $P_n^{(\alpha,\beta)}$ are defined by
$$\dfrac{2^{\alpha+\beta}}{\sqrt{1-2xt+t^2}\left(1-t+ \sqrt{1-2xt+t^2} \right)^{\alpha} \left(1+t+\sqrt{1-2xt+t^2} \right)^{\beta}}$$
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$$P_n^{(\alpha,\beta)}(z)=\dfrac{(\alpha+1)^{\overline{n}}}{n!} {}_2F_1 \left(-n, 1+\alpha+\beta+n;\alpha+1; \dfrac{1}{2}(1-z) \right),$$
in the sense that
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where ${}_2F_1$ is the [[Hypergeometric pFq|generalized hypergeometries series]].
$$\dfrac{2^{\alpha+\beta}}{\sqrt{1-2xt+t^2}\left(1-t+ \sqrt{1-2xt+t^2} \right)^{\alpha} \left(1+t+\sqrt{1-2xt+t^2} \right)^{\beta}} =  \sum_{k=0}^{\infty} P_k^{(\alpha,\beta)}(x)t^k$$
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holds.
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=Properties=
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<div class="toccolours mw-collapsible mw-collapsed">
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<strong>Theorem:</strong> ([[Rodrigues' formula]]) The following formula holds:
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$$P_n^{(\alpha,\beta)}(z)=\dfrac{(-1)^n}{2^nn!} (1-z)^{-\alpha}(1+z)^{-\beta} \dfrac{d^n}{dz^n} \left[(1-z)^{\alpha}(1+z)^{\beta}(1-z^2)^n \right].$$  
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<div class="mw-collapsible-content">
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<strong>Proof:</strong> █
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</div>
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</div>
  
 
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Revision as of 20:17, 23 March 2015

The Jacobi polynomial $P_n^{(\alpha,\beta)}$ are defined by $$P_n^{(\alpha,\beta)}(z)=\dfrac{(\alpha+1)^{\overline{n}}}{n!} {}_2F_1 \left(-n, 1+\alpha+\beta+n;\alpha+1; \dfrac{1}{2}(1-z) \right),$$ where ${}_2F_1$ is the generalized hypergeometries series.

Properties

Theorem: (Rodrigues' formula) The following formula holds: $$P_n^{(\alpha,\beta)}(z)=\dfrac{(-1)^n}{2^nn!} (1-z)^{-\alpha}(1+z)^{-\beta} \dfrac{d^n}{dz^n} \left[(1-z)^{\alpha}(1+z)^{\beta}(1-z^2)^n \right].$$

Proof:

Orthogonal polynomials