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23 Weierstrass Elliptic and Modular FunctionsWeierstrass Elliptic Functions

§23.6 Relations to Other Functions

Contents

§23.6(i) Theta Functions

In this subsection 2\omega_{1}, 2\omega_{3} are any pair of generators of the lattice \mathbb{L}, and the lattice roots e_{1}, e_{2}, e_{3} are given by (23.3.9).

23.6.1
q=e^{{i\pi\tau}},
\tau=\omega_{3}/\omega_{1}.
23.6.2e_{1}=\frac{\pi^{2}}{12\omega_{1}^{2}}\left({\mathop{\theta_{{2}}\/}\nolimits^%
{{4}}}\!\left(0,q\right)+2\!{\mathop{\theta_{{4}}\/}\nolimits^{{4}}}\!\left(0,%
q\right)\right),
23.6.3e_{2}=\frac{\pi^{2}}{12\omega_{1}^{2}}\left({\mathop{\theta_{{2}}\/}\nolimits^%
{{4}}}\!\left(0,q\right)-{\mathop{\theta_{{4}}\/}\nolimits^{{4}}}\!\left(0,q%
\right)\right),
23.6.4e_{3}=-\frac{\pi^{2}}{12\omega_{1}^{2}}\left(2\!{\mathop{\theta_{{2}}\/}%
\nolimits^{{4}}}\!\left(0,q\right)+{\mathop{\theta_{{4}}\/}\nolimits^{{4}}}\!%
\left(0,q\right)\right).
23.6.8\eta_{1}=-\frac{\pi^{2}}{12\omega_{1}}\frac{{\mathop{\theta_{{1}}\/}\nolimits^%
{{\prime\prime\prime}}}\!\left(0,q\right)}{{\mathop{\theta_{{1}}\/}\nolimits^{%
{\prime}}}\!\left(0,q\right)}.

With z=\ifrac{\pi u}{(2\omega_{1})},

For further results for the \mathop{\sigma\/}\nolimits-function see Lawden (1989, §6.2).

§23.6(ii) Jacobian Elliptic Functions

Again, in Equations (23.6.16)–(23.6.26), 2\omega_{1},2\omega_{3} are any pair of generators of the lattice \mathbb{L} and e_{1},e_{2},e_{3} are given by (23.3.9).

23.6.16
k^{2}=\frac{e_{2}-e_{3}}{e_{1}-e_{3}},
{k^{{\prime}}}^{2}=\frac{e_{1}-e_{2}}{e_{1}-e_{3}},

Similar results for the other nine Jacobi functions can be constructed with the aid of the transformations given by Table 22.4.3.

For representations of the Jacobi functions \mathop{\mathrm{sn}\/}\nolimits, \mathop{\mathrm{cn}\/}\nolimits, and \mathop{\mathrm{dn}\/}\nolimits as quotients of \mathop{\sigma\/}\nolimits-functions see Lawden (1989, §§6.2, 6.3).

§23.6(iii) General Elliptic Functions

For representations of general elliptic functions (§23.2(iii)) in terms of \mathop{\sigma\/}\nolimits\!\left(z\right) and \mathop{\wp\/}\nolimits\!\left(z\right) see Lawden (1989, §§8.9, 8.10), and for expansions in terms of \mathop{\zeta\/}\nolimits\!\left(z\right) see Lawden (1989, §8.11).

§23.6(iv) Elliptic Integrals

Rectangular Lattice

Let z be on the perimeter of the rectangle with vertices 0,2\omega_{1},2\omega_{1}+2\omega_{3},2\omega_{3}. Then t=\mathop{\wp\/}\nolimits\!\left(z\right) is real (§§23.5(i)23.5(ii)), and

For (23.6.30)–(23.6.35) and further identities see Lawden (1989, §6.12).

See also §§19.2(i), 19.14, and Erdélyi et al. (1953b, §13.14).

For relations to symmetric elliptic integrals see §19.25(vi).

General Lattice

Let z be a point of \Complex different from e_{1},e_{2},e_{3}, and define w by

where the integral is taken along any path from z to \infty that does not pass through any of e_{1},e_{2},e_{3}. Then z=\mathop{\wp\/}\nolimits\!\left(w\right), where the value of w depends on the choice of path and determination of the square root; see McKean and Moll (1999, pp. 87–88 and §2.5).