About the Project
29 Lamé FunctionsLamé Functions

§29.6 Fourier Series

Contents
  1. §29.6(i) Function \mathit{Ec}^{2m}_{\nu}\left(z,k^{2}\right)
  2. §29.6(ii) Function \mathit{Ec}^{2m+1}_{\nu}\left(z,k^{2}\right)
  3. §29.6(iii) Function \mathit{Es}^{2m+1}_{\nu}\left(z,k^{2}\right)
  4. §29.6(iv) Function \mathit{Es}^{2m+2}_{\nu}\left(z,k^{2}\right)

§29.6(i) Function \mathit{Ec}^{2m}_{\nu}\left(z,k^{2}\right)

With \phi=\frac{1}{2}\pi-\operatorname{am}\left(z,k\right), as in (29.2.5), we have

Here

29.6.2 H=2a^{2m}_{\nu}\left(k^{2}\right)-\nu(\nu+1)k^{2},
29.6.3 (\beta_{0}-H)A_{0}+\alpha_{0}A_{2}=0,
29.6.4 \gamma_{p}A_{2p-2}+(\beta_{p}-H)A_{2p}+\alpha_{p}A_{2p+2}=0,p\geq 1,

with \alpha_{p}, \beta_{p}, and \gamma_{p} as in (29.3.11) and (29.3.12), and

29.6.5 \tfrac{1}{2}A_{0}^{2}+\sum_{p=1}^{\infty}A_{2p}^{2}=1,
29.6.6 \tfrac{1}{2}A_{0}+\sum_{p=1}^{\infty}A_{2p}>0.

When \nu\neq 2n, where n is a nonnegative integer, it follows from §2.9(i) that for any value of H the system (29.6.4)–(29.6.6) has a unique recessive solution A_{0},A_{2},A_{4},\dots; furthermore

In addition, if H satisfies (29.6.2), then (29.6.3) applies.

In the special case \nu=2n, m=0,1,\dots,n, there is a unique nontrivial solution with the property A_{2p}=0, p=n+1,n+2,\dots. This solution can be constructed from (29.6.4) by backward recursion, starting with A_{2n+2}=0 and an arbitrary nonzero value of A_{2n}, followed by normalization via (29.6.5) and (29.6.6). Consequently, \mathit{Ec}^{2m}_{\nu}\left(z,k^{2}\right) reduces to a Lamé polynomial; compare §§29.12(i) and 29.15(i).

An alternative version of the Fourier series expansion (29.6.1) is given by

Here \operatorname{dn}\left(z,k\right) is as in §22.2, and

29.6.9 (\beta_{0}-H)C_{0}+\alpha_{0}C_{2}=0,
29.6.10 \gamma_{p}C_{2p-2}+(\beta_{p}-H)C_{2p}+\alpha_{p}C_{2p+2}=0,p\geq 1,

with \alpha_{p},\beta_{p}, and \gamma_{p} now defined by

29.6.11
\alpha_{p}=\begin{cases}\nu(\nu+1)k^{2},&p=0,\\
\frac{1}{2}(\nu-2p)(\nu+2p+1)k^{2},&p\geq 1,\end{cases}
\beta_{p}=4p^{2}(2-k^{2}),
\gamma_{p}=\tfrac{1}{2}(\nu-2p+1)(\nu+2p)k^{2},

and

29.6.12 \left(1-\tfrac{1}{2}k^{2}\right)\left(\tfrac{1}{2}C_{0}^{2}+\sum_{p=1}^{\infty%
}C_{2p}^{2}\right)-\tfrac{1}{2}k^{2}\sum_{p=0}^{\infty}C_{2p}C_{2p+2}=1,
29.6.13 \tfrac{1}{2}C_{0}+\sum_{p=1}^{\infty}C_{2p}>0,

§29.6(ii) Function \mathit{Ec}^{2m+1}_{\nu}\left(z,k^{2}\right)

Here

29.6.17 H=2a^{2m+1}_{\nu}\left(k^{2}\right)-\nu(\nu+1)k^{2},
29.6.18 (\beta_{0}-H)A_{1}+\alpha_{0}A_{3}=0,
29.6.19 \gamma_{p}A_{2p-1}+(\beta_{p}-H)A_{2p+1}+\alpha_{p}A_{2p+3}=0,p\geq 1,

with \alpha_{p}, \beta_{p}, and \gamma_{p} as in (29.3.13) and (29.3.14), and

29.6.20 \sum_{p=0}^{\infty}A_{2p+1}^{2}=1,
29.6.21 \sum_{p=0}^{\infty}A_{2p+1}>0,

Also,

where

29.6.24 (\beta_{0}-H)C_{1}+\alpha_{0}C_{3}=0,
29.6.25 \gamma_{p}C_{2p-1}+(\beta_{p}-H)C_{2p+1}+\alpha_{p}C_{2p+3}=0,p\geq 1,

with

29.6.26
\alpha_{p}=\tfrac{1}{2}(\nu-2p-1)(\nu+2p+2)k^{2},
\beta_{p}=\begin{cases}2-k^{2}+\frac{1}{2}\nu(\nu+1)k^{2},&p=0,\\
(2p+1)^{2}(2-k^{2}),&p\geq 1,\end{cases}
\gamma_{p}=\tfrac{1}{2}(\nu-2p)(\nu+2p+1)k^{2},

and

29.6.27 \left(1-\tfrac{1}{2}k^{2}\right)\sum_{p=0}^{\infty}C_{2p+1}^{2}-{\tfrac{1}{2}k%
^{2}\left(\tfrac{1}{2}C_{1}^{2}+\sum_{p=0}^{\infty}C_{2p+1}C_{2p+3}\right)=1},
29.6.28 \sum_{p=0}^{\infty}C_{2p+1}>0,

§29.6(iii) Function \mathit{Es}^{2m+1}_{\nu}\left(z,k^{2}\right)

Here

29.6.32 H=2b^{2m+1}_{\nu}\left(k^{2}\right)-\nu(\nu+1)k^{2},
29.6.33 (\beta_{0}-H)B_{1}+\alpha_{0}B_{3}=0,
29.6.34 \gamma_{p}B_{2p-1}+(\beta_{p}-H)B_{2p+1}+\alpha_{p}B_{2p+3}=0,p\geq 1,

with \alpha_{p}, \beta_{p}, and \gamma_{p} as in (29.3.15), (29.3.16), and

29.6.35 \sum_{p=0}^{\infty}B_{2p+1}^{2}=1,
29.6.36 \sum_{p=0}^{\infty}(2p+1)B_{2p+1}>0,

Also,

where

29.6.39 (\beta_{0}-H)D_{1}+\alpha_{0}D_{3}=0,
29.6.40 \gamma_{p}D_{2p-1}+(\beta_{p}-H)D_{2p+1}+\alpha_{p}D_{2p+3}=0,p\geq 1,

with

29.6.41
\alpha_{p}=\tfrac{1}{2}(\nu-2p-1)(\nu+2p+2)k^{2},
\beta_{p}=\begin{cases}2-k^{2}-\frac{1}{2}\nu(\nu+1)k^{2},&p=0,\\
(2p+1)^{2}(2-k^{2}),&p\geq 1,\end{cases}
\gamma_{p}=\tfrac{1}{2}(\nu-2p)(\nu+2p+1)k^{2},

and

29.6.42 \left(1-\tfrac{1}{2}k^{2}\right)\sum_{p=0}^{\infty}D_{2p+1}^{2}+{\tfrac{1}{2}k%
^{2}\left(\tfrac{1}{2}D_{1}^{2}-\sum_{p=0}^{\infty}D_{2p+1}D_{2p+3}\right)=1},
29.6.43 \sum_{p=0}^{\infty}(2p+1)D_{2p+1}>0,

§29.6(iv) Function \mathit{Es}^{2m+2}_{\nu}\left(z,k^{2}\right)

Here

29.6.47 H=2b^{2m+2}_{\nu}\left(k^{2}\right)-\nu(\nu+1)k^{2},
29.6.48 (\beta_{0}-H)B_{2}+\alpha_{0}B_{4}=0,
29.6.49 \gamma_{p}B_{2p}+(\beta_{p}-H)B_{2p+2}+\alpha_{p}B_{2p+4}=0,p\geq 1,

with \alpha_{p}, \beta_{p}, and \gamma_{p} as in (29.3.17), and

29.6.50 \sum_{p=1}^{\infty}B_{2p}^{2}=1,
29.6.51 \sum_{p=0}^{\infty}(2p+2)B_{2p+2}>0,

Also,

where

29.6.54 (\beta_{0}-H)D_{2}+\alpha_{0}D_{4}=0,
29.6.55 \gamma_{p}D_{2p}+(\beta_{p}-H)D_{2p+2}+\alpha_{p}D_{2p+4}=0,p\geq 1,

with

29.6.56
\alpha_{p}=\tfrac{1}{2}(\nu-2p-2)(\nu+2p+3)k^{2},
\beta_{p}=(2p+2)^{2}(2-k^{2}),
\gamma_{p}=\tfrac{1}{2}(\nu-2p-1)(\nu+2p+2)k^{2},

and

29.6.57 \left(1-\tfrac{1}{2}k^{2}\right)\sum_{p=1}^{\infty}D_{2p}^{2}-\tfrac{1}{2}k^{2%
}\sum_{p=1}^{\infty}D_{2p}D_{2p+2}=1,
29.6.58 \sum_{p=0}^{\infty}(2p+2)D_{2p+2}>0,