# §23.6 Relations to Other Functions

## §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 $\displaystyle q$ $\displaystyle=e^{i\pi\tau},$ $\displaystyle\tau$ $\displaystyle=\omega_{3}/\omega_{1}.$
 23.6.2 $\displaystyle e_{1}$ $\displaystyle=\frac{\pi^{2}}{12\omega_{1}^{2}}\left({\mathop{\theta_{2}\/}% \nolimits^{4}}\!\left(0,q\right)+2\!{\mathop{\theta_{4}\/}\nolimits^{4}}\!% \left(0,q\right)\right),$ Symbols: $\mathop{\theta_{\NVar{j}}\/}\nolimits\!\left(\NVar{z},\NVar{q}\right)$: theta function, $\pi$: the ratio of the circumference of a circle to its diameter, $q$: nome, $e_{j}$: zeros and $\omega_{1}$, $\omega_{3}$, $\omega_{2}=-\omega_{1}-\omega_{3}$: lattice generators A&S Ref: 18.10.12, 18.10.13, 18.10.14, and 18.10.9, 18.10.10, 18.10.11 Referenced by: §23.22(ii), §23.22(i), §23.22(ii), §23.6(i), §23.6(ii) Permalink: http://dlmf.nist.gov/23.6.E2 Encodings: TeX, pMML, png See also: Annotations for 23.6(i) 23.6.3 $\displaystyle e_{2}$ $\displaystyle=\frac{\pi^{2}}{12\omega_{1}^{2}}\left({\mathop{\theta_{2}\/}% \nolimits^{4}}\!\left(0,q\right)-{\mathop{\theta_{4}\/}\nolimits^{4}}\!\left(0% ,q\right)\right),$ Symbols: $\mathop{\theta_{\NVar{j}}\/}\nolimits\!\left(\NVar{z},\NVar{q}\right)$: theta function, $\pi$: the ratio of the circumference of a circle to its diameter, $q$: nome, $e_{j}$: zeros and $\omega_{1}$, $\omega_{3}$, $\omega_{2}=-\omega_{1}-\omega_{3}$: lattice generators A&S Ref: 18.10.12, 18.10.13, 18.10.14, and 18.10.9, 18.10.10, 18.10.11 Permalink: http://dlmf.nist.gov/23.6.E3 Encodings: TeX, pMML, png See also: Annotations for 23.6(i) 23.6.4 $\displaystyle e_{3}$ $\displaystyle=-\frac{\pi^{2}}{12\omega_{1}^{2}}\left(2\!{\mathop{\theta_{2}\/}% \nolimits^{4}}\!\left(0,q\right)+{\mathop{\theta_{4}\/}\nolimits^{4}}\!\left(0% ,q\right)\right).$ Symbols: $\mathop{\theta_{\NVar{j}}\/}\nolimits\!\left(\NVar{z},\NVar{q}\right)$: theta function, $\pi$: the ratio of the circumference of a circle to its diameter, $q$: nome, $e_{j}$: zeros and $\omega_{1}$, $\omega_{3}$, $\omega_{2}=-\omega_{1}-\omega_{3}$: lattice generators A&S Ref: 18.10.12, 18.10.13, 18.10.14, and 18.10.9, 18.10.10, 18.10.11 Referenced by: §23.22(ii), §23.22(ii), §23.6(ii) Permalink: http://dlmf.nist.gov/23.6.E4 Encodings: TeX, pMML, png See also: Annotations for 23.6(i)
 23.6.5 $\displaystyle\mathop{\wp\/}\nolimits\!\left(z\right)-e_{1}$ $\displaystyle=\left(\frac{\pi\mathop{\theta_{3}\/}\nolimits\!\left(0,q\right)% \mathop{\theta_{4}\/}\nolimits\!\left(0,q\right)\mathop{\theta_{2}\/}\nolimits% \!\left(\pi z/(2\omega_{1}),q\right)}{2\omega_{1}\mathop{\theta_{1}\/}% \nolimits\!\left(\pi z/(2\omega_{1}),q\right)}\right)^{2},$ 23.6.6 $\displaystyle\mathop{\wp\/}\nolimits\!\left(z\right)-e_{2}$ $\displaystyle=\left(\frac{\pi\mathop{\theta_{2}\/}\nolimits\!\left(0,q\right)% \mathop{\theta_{4}\/}\nolimits\!\left(0,q\right)\mathop{\theta_{3}\/}\nolimits% \!\left(\pi z/(2\omega_{1}),q\right)}{2\omega_{1}\mathop{\theta_{1}\/}% \nolimits\!\left(\pi z/(2\omega_{1}),q\right)}\right)^{2},$ 23.6.7 $\displaystyle\mathop{\wp\/}\nolimits\!\left(z\right)-e_{3}$ $\displaystyle=\left(\frac{\pi\mathop{\theta_{2}\/}\nolimits\!\left(0,q\right)% \mathop{\theta_{3}\/}\nolimits\!\left(0,q\right)\mathop{\theta_{4}\/}\nolimits% \!\left(\pi z/(2\omega_{1}),q\right)}{2\omega_{1}\mathop{\theta_{1}\/}% \nolimits\!\left(\pi z/(2\omega_{1}),q\right)}\right)^{2}.$
 23.6.8 $\eta_{1}=-\frac{\pi^{2}}{12\omega_{1}}\frac{\mathop{\theta_{1}\/}\nolimits'''% \!\left(0,q\right)}{\mathop{\theta_{1}\/}\nolimits'\!\left(0,q\right)}.$
 23.6.9 $\mathop{\sigma\/}\nolimits\!\left(z\right)=2\omega_{1}\mathop{\exp\/}\nolimits% \!\left(\frac{\eta_{1}z^{2}}{2\omega_{1}}\right)\frac{\mathop{\theta_{1}\/}% \nolimits\!\left(\pi z/(2\omega_{1}),q\right)}{\pi\mathop{\theta_{1}\/}% \nolimits'\!\left(0,q\right)},$
 23.6.10 $\displaystyle\mathop{\sigma\/}\nolimits\!\left(\omega_{1}\right)$ $\displaystyle=2\omega_{1}\frac{\mathop{\exp\/}\nolimits\!\left(\tfrac{1}{2}% \eta_{1}\omega_{1}\right)\mathop{\theta_{2}\/}\nolimits\!\left(0,q\right)}{\pi% \mathop{\theta_{1}\/}\nolimits'\!\left(0,q\right)},$ 23.6.11 $\displaystyle\mathop{\sigma\/}\nolimits\!\left(\omega_{2}\right)$ $\displaystyle=2\omega_{1}i\frac{\mathop{\exp\/}\nolimits\!\left(\tfrac{1}{2}% \eta_{1}\omega_{1}\tau^{2}\right)\mathop{\theta_{3}\/}\nolimits\!\left(0,q% \right)}{\pi q^{1/4}\mathop{\theta_{1}\/}\nolimits'\!\left(0,q\right)},$ 23.6.12 $\displaystyle\mathop{\sigma\/}\nolimits\!\left(\omega_{3}\right)$ $\displaystyle=-2\omega_{1}\frac{\mathop{\exp\/}\nolimits\!\left(\tfrac{1}{2}% \eta_{1}\omega_{1}\right)\mathop{\theta_{4}\/}\nolimits\!\left(0,q\right)}{\pi q% ^{1/4}\mathop{\theta_{1}\/}\nolimits'\!\left(0,q\right)}.$

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

 23.6.13 $\mathop{\zeta\/}\nolimits\!\left(u\right)=\frac{\eta_{1}}{\omega_{1}}u+\frac{% \pi}{2\omega_{1}}\frac{\mathrm{d}}{\mathrm{d}z}\mathop{\ln\/}\nolimits\mathop{% \theta_{1}\/}\nolimits\!\left(z,q\right),$
 23.6.14 $\mathop{\wp\/}\nolimits\!\left(u\right)=\left(\frac{\pi}{2\omega_{1}}\right)^{% 2}\left(\frac{\mathop{\theta_{1}\/}\nolimits'''\!\left(0,q\right)}{3\!\mathop{% \theta_{1}\/}\nolimits'\!\left(0,q\right)}-\frac{{\mathrm{d}}^{2}}{{\mathrm{d}% z}^{2}}\mathop{\ln\/}\nolimits\mathop{\theta_{1}\/}\nolimits\!\left(z,q\right)% \right),$
 23.6.15 $\frac{\mathop{\sigma\/}\nolimits\!\left(u+\omega_{j}\right)}{\mathop{\sigma\/}% \nolimits\!\left(\omega_{j}\right)}=\mathop{\exp\/}\nolimits\!\left(\eta_{j}u+% \frac{\eta_{j}u^{2}}{2\omega_{1}}\right)\frac{\mathop{\theta_{j+1}\/}\nolimits% \!\left(z,q\right)}{\mathop{\theta_{j+1}\/}\nolimits\!\left(0,q\right)},$ $j=1,2,3$.

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 $\displaystyle k^{2}$ $\displaystyle=\frac{e_{2}-e_{3}}{e_{1}-e_{3}},$ $\displaystyle{k^{\prime}}^{2}$ $\displaystyle=\frac{e_{1}-e_{2}}{e_{1}-e_{3}},$ Symbols: $e_{j}$: zeros, $k$: modulus and $k^{\prime}$: complementary modulus A&S Ref: 18.9.9 Referenced by: (a), §23.6(ii), §23.6(ii) Permalink: http://dlmf.nist.gov/23.6.E16 Encodings: TeX, TeX, pMML, pMML, png, png See also: Annotations for 23.6(ii)
 23.6.17 $\displaystyle{\mathop{K\/}\nolimits^{2}}$ $\displaystyle=(\mathop{K\/}\nolimits\!\left(k\right))^{2}=\omega_{1}^{2}(e_{1}% -e_{3}),$ $\displaystyle{\mathop{{K^{\prime}}\/}\nolimits^{2}}$ $\displaystyle=(\mathop{K\/}\nolimits\!\left(k^{\prime}\right))^{2}=\omega_{3}^% {2}(e_{3}-e_{1}).$
 23.6.18 $\displaystyle e_{1}$ $\displaystyle=\frac{{\mathop{K\/}\nolimits^{2}}}{3\omega_{1}^{2}}(1+{k^{\prime% }}^{2}),$ 23.6.19 $\displaystyle e_{2}$ $\displaystyle=\frac{{\mathop{K\/}\nolimits^{2}}}{3\omega_{1}^{2}}(k^{2}-{k^{% \prime}}^{2}),$ 23.6.20 $\displaystyle e_{3}$ $\displaystyle=-\frac{{\mathop{K\/}\nolimits^{2}}}{3\omega_{1}^{2}}(1+k^{2}).$
 23.6.21 $\displaystyle\mathop{\wp\/}\nolimits\!\left(z\right)-e_{1}$ $\displaystyle=\frac{{\mathop{K\/}\nolimits^{2}}}{\omega_{1}^{2}}{\mathop{% \mathrm{cs}\/}\nolimits^{2}}\left(\frac{\mathop{K\/}\nolimits\!z}{\omega_{1}},% k\right),$ 23.6.22 $\displaystyle\mathop{\wp\/}\nolimits\!\left(z\right)-e_{2}$ $\displaystyle=\frac{{\mathop{K\/}\nolimits^{2}}}{\omega_{1}^{2}}{\mathop{% \mathrm{ds}\/}\nolimits^{2}}\left(\frac{\mathop{K\/}\nolimits\!z}{\omega_{1}},% k\right),$ 23.6.23 $\displaystyle\mathop{\wp\/}\nolimits\!\left(z\right)-e_{3}$ $\displaystyle=\frac{{\mathop{K\/}\nolimits^{2}}}{\omega_{1}^{2}}{\mathop{% \mathrm{ns}\/}\nolimits^{2}}\left(\frac{\mathop{K\/}\nolimits\!z}{\omega_{1}},% k\right).$
 23.6.24 $\displaystyle\mathop{\wp\/}\nolimits\!\left(z+\omega_{1}\right)-e_{1}$ $\displaystyle=\left(\frac{\mathop{K\/}\nolimits\!k^{\prime}}{\omega_{1}}\right% )^{2}{\mathop{\mathrm{sc}\/}\nolimits^{2}}\left(\frac{\mathop{K\/}\nolimits\!z% }{\omega_{1}},k\right),$ 23.6.25 $\displaystyle\mathop{\wp\/}\nolimits\!\left(z+\omega_{2}\right)-e_{2}$ $\displaystyle=-\left(\frac{\mathop{K\/}\nolimits\!kk^{\prime}}{\omega_{1}}% \right)^{2}{\mathop{\mathrm{sd}\/}\nolimits^{2}}\left(\frac{\mathop{K\/}% \nolimits\!z}{\omega_{1}},k\right),$ 23.6.26 $\displaystyle\mathop{\wp\/}\nolimits\!\left(z+\omega_{3}\right)-e_{3}$ $\displaystyle=\left(\frac{\mathop{K\/}\nolimits\!k}{\omega_{1}}\right)^{2}{% \mathop{\mathrm{sn}\/}\nolimits^{2}}\left(\frac{\mathop{K\/}\nolimits\!z}{% \omega_{1}},k\right).$

In (23.6.27)–(23.6.29) the modulus $k$ is given and $\mathop{K\/}\nolimits=\mathop{K\/}\nolimits\!\left(k\right)$, $\mathop{{K^{\prime}}\/}\nolimits=\mathop{K\/}\nolimits\!\left(k^{\prime}\right)$ are the corresponding complete elliptic integrals (§19.2(ii)). Also, $\mathbb{L}_{\mspace{1.0mu }1}$, $\mathbb{L}_{\mspace{1.0mu }2}$, $\mathbb{L}_{\mspace{1.0mu }3}$ are the lattices with generators $(4\!\mathop{K\/}\nolimits,2\mathrm{i}\mathop{{K^{\prime}}\/}\nolimits)$, $(2\!\mathop{K\/}\nolimits-2\mathrm{i}\mathop{{K^{\prime}}\/}\nolimits,2\!% \mathop{K\/}\nolimits+2\mathrm{i}\mathop{{K^{\prime}}\/}\nolimits)$, $(2\!\mathop{K\/}\nolimits,4\mathrm{i}\mathop{{K^{\prime}}\/}\nolimits)$, respectively.

 23.6.27 $\mathop{\zeta\/}\nolimits\!\left(z|\mathbb{L}_{\mspace{1.0mu }1}\right)-% \mathop{\zeta\/}\nolimits\!\left(z+2\!\mathop{K\/}\nolimits|\mathbb{L}_{% \mspace{1.0mu }1}\right)+\mathop{\zeta\/}\nolimits\!\left(2\!\mathop{K\/}% \nolimits|\mathbb{L}_{\mspace{1.0mu }1}\right)=\mathop{\mathrm{ns}\/}\nolimits% \left(z,k\right),$
 23.6.28 $\mathop{\zeta\/}\nolimits\!\left(z|\mathbb{L}_{\mspace{1.0mu }2}\right)-% \mathop{\zeta\/}\nolimits\!\left(z+2\!\mathop{K\/}\nolimits|\mathbb{L}_{% \mspace{1.0mu }2}\right)+\mathop{\zeta\/}\nolimits\!\left(2\!\mathop{K\/}% \nolimits|\mathbb{L}_{\mspace{1.0mu }2}\right)=\mathop{\mathrm{ds}\/}\nolimits% \left(z,k\right),$
 23.6.29 $\mathop{\zeta\/}\nolimits\!\left(z|\mathbb{L}_{\mspace{1.0mu }3}\right)-% \mathop{\zeta\/}\nolimits\!\left(z+2\mathrm{i}\!\mathop{{K^{\prime}}\/}% \nolimits|\mathbb{L}_{\mspace{1.0mu }3}\right)-\mathop{\zeta\/}\nolimits\!% \left(2\mathrm{i}\!\mathop{{K^{\prime}}\/}\nolimits|\mathbb{L}_{\mspace{1.0mu % }3}\right)=\mathop{\mathrm{cs}\/}\nolimits\left(z,k\right).$

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

 23.6.30 $z=\frac{1}{2}\int_{t}^{\infty}\frac{\mathrm{d}u}{\sqrt{(u-e_{1})(u-e_{2})(u-e_% {3})}},$ $t\geq e_{1}$, $z\in(0,\omega_{1}]$,
 23.6.31 $\displaystyle z-\omega_{1}$ $\displaystyle=\frac{i}{2}\int_{t}^{e_{1}}\frac{\mathrm{d}u}{\sqrt{(e_{1}-u)(u-% e_{2})(u-e_{3})}},$ $e_{2}\leq t\leq e_{1}$, $z\in[\omega_{1},\omega_{1}+\omega_{3}]$, 23.6.32 $\displaystyle z-\omega_{3}$ $\displaystyle=\frac{1}{2}\int_{e_{3}}^{t}\frac{\mathrm{d}u}{\sqrt{(e_{1}-u)(e_% {2}-u)(u-e_{3})}},$ $e_{3}\leq t\leq e_{2}$, $z\in[\omega_{3},\omega_{1}+\omega_{3}]$,
 23.6.33 $z=\frac{i}{2}\int_{-\infty}^{t}\frac{\mathrm{d}u}{\sqrt{(e_{1}-u)(e_{2}-u)(e_{% 3}-u)}},$ $t\leq e_{3}$, $z\in(0,\omega_{3}]$.
 23.6.34 $2\omega_{1}=\int_{e_{1}}^{\infty}\frac{\mathrm{d}u}{\sqrt{(u-e_{1})(u-e_{2})(u% -e_{3})}}=\int_{e_{3}}^{e_{2}}\frac{\mathrm{d}u}{\sqrt{(e_{1}-u)(e_{2}-u)(u-e_% {3})}},$
 23.6.35 $2\omega_{3}=i\int_{e_{2}}^{e_{1}}\frac{\mathrm{d}u}{\sqrt{(e_{1}-u)(u-e_{2})(u% -e_{3})}}=i\int_{-\infty}^{e_{3}}\frac{\mathrm{d}u}{\sqrt{(e_{1}-u)(e_{2}-u)(e% _{3}-u)}}.$

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

Let $z$ be a point of $\mathbb{C}$ different from $e_{1},e_{2},e_{3}$, and define $w$ by
 23.6.36 $w=\int_{z}^{\infty}\frac{\mathrm{d}u}{\sqrt{4u^{3}-g_{2}u-g_{3}}}=\frac{1}{2}% \int_{z}^{\infty}\frac{\mathrm{d}u}{\sqrt{(u-e_{1})(u-e_{2})(u-e_{3})}},$
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).