A spheroidal harmonic is a special case of the Ellipsoidal Harmonic which satisfies the
differential equation
See also Ellipsoidal Harmonic
References
Press, W. H.; Flannery, B. P.; Teukolsky, S. A.; and Vetterling, W. T. ``A Worked Example: Spheroidal Harmonics.'' §17.4 in
Numerical Recipes in FORTRAN: The Art of Scientific Computing, 2nd ed. Cambridge, England:
Cambridge University Press, pp. 764-773, 1992.