30 Spheroidal Wave Functions30.2 Differential Equations

§30.1 Special Notation

(For other notation see Notation for the Special Functions.)

x real variable. Except in §§30.7(iv), 30.11(ii), 30.13, and 30.14, -1<x<1.
\gamma^{2} real parameter (positive, zero, or negative).
m order, a nonnegative integer.
n degree, an integer n=m,m+1,m+2,\dots.
k integer.
\delta arbitrary small positive constant.

The main functions treated in this chapter are the eigenvalues \mathop{\lambda^{{m}}_{{n}}\/}\nolimits\!\left(\gamma^{2}\right) and the spheroidal wave functions \mathop{\mathsf{Ps}^{{m}}_{{n}}\/}\nolimits\!\left(x,\gamma^{2}\right), \mathop{\mathsf{Qs}^{{m}}_{{n}}\/}\nolimits\!\left(x,\gamma^{2}\right), \mathop{\mathit{Ps}^{{m}}_{{n}}\/}\nolimits\!\left(z,\gamma^{2}\right), \mathop{\mathit{Qs}^{{m}}_{{n}}\/}\nolimits\!\left(z,\gamma^{2}\right), and \mathop{S^{{m(j)}}_{{n}}\/}\nolimits\!\left(z,\gamma\right), j=1,2,3,4. These notations are similar to those used in Arscott (1964b) and Erdélyi et al. (1955). Meixner and Schäfke (1954) use \mathrm{ps}, \mathrm{qs}, \mathrm{Ps}, \mathrm{Qs} for \mathop{\mathsf{Ps}\/}\nolimits, \mathop{\mathsf{Qs}\/}\nolimits, \mathop{\mathit{Ps}\/}\nolimits, \mathop{\mathit{Qs}\/}\nolimits, respectively.

Other Notations

Flammer (1957) and Abramowitz and Stegun (1964) use \lambda _{{mn}}(\gamma) for \mathop{\lambda^{{m}}_{{n}}\/}\nolimits\!\left(\gamma^{2}\right)+\gamma^{2}, R_{{mn}}^{{(j)}}(\gamma,z) for \mathop{S^{{m(j)}}_{{n}}\/}\nolimits\!\left(z,\gamma\right), and

30.1.1
S^{{(1)}}_{{mn}}(\gamma,x)=d_{{mn}}(\gamma)\mathop{\mathsf{Ps}^{{m}}_{{n}}\/}\nolimits\!\left(x,\gamma^{2}\right),
S^{{(2)}}_{{mn}}(\gamma,x)=d_{{mn}}(\gamma)\mathop{\mathsf{Qs}^{{m}}_{{n}}\/}\nolimits\!\left(x,\gamma^{2}\right),

where d_{{mn}}(\gamma) is a normalization constant determined by

30.1.2
S^{{(1)}}_{{mn}}(\gamma,0)=(-1)^{m}\mathop{\mathsf{P}^{{m}}_{{n}}\/}\nolimits\!\left(0\right),n-m even,
\left.\frac{d}{dx}S^{{(1)}}_{{mn}}(\gamma,x)\right|_{{x=0}}=(-1)^{m}\left.\frac{d}{dx}\mathop{\mathsf{P}^{{m}}_{{n}}\/}\nolimits\!\left(x\right)\right|_{{x=0}},n-m odd.

For older notations see Abramowitz and Stegun (1964, §21.11) and Flammer (1957, pp. 14,15).