English

Inverse spherical Bessel functions generalize Lambert W and solve similar equations containing trigonometric or hyperbolic subexpressions or their inverses

General Mathematics 2022-09-07 v4

Abstract

A strict integer Laurent polynomial in a variable xx is 0 or a sum of one or more terms having integer coefficients times xx raised to a negative integer exponent. Equations that can be transformed to certain such polynomials times exp(x)=constant\exp(-x)=\mathit{constant} are exactly solvable by inverses of modified spherical Bessel functions of the second kind kn(x)k_{n}(x) where nn is the order, generalizing the Lambert WW function when n>0.n>0. Equations that can be converted to certain such polynomials times cos(x)\cos(x) or such polynomials times sin(x)\sin(x) or a sum thereof =constant=\mathit{constant} are exactly solvable by inverses of spherical Bessel functions yn(x)y_{n}(x) or jn(x)j_{n}(x). Such equations include cos(x)/x=constant\cos(x)/x=\mathit{constant}, for which the solution inverse1(y0)(constant)\mathrm{inverse}_{1}(y_{0})(\mathit{-constant}) is Dottie's number when constant=1\mathit{constant}=1, where subscript 1 is the branch number. Equations that can be converted to certain strict integer Laurent polynomials times sinh(x)\sinh(x) and possibly also plus such a polynomial times cosh(x)\cosh(x) are exactly solvable by inverses of modified spherical Bessel functions of the first kind in(x)i_{n}(x). These discoveries arose from the AskConstants program surprisingly proposing the explicit exact closed form inverse1(y0)(1)\mathrm{inverse}_{1}(y_{0})(-1) for the approximate input 0.739085133215160642, because no explicit exact closed form representation was known for Dottie's number from approximately 1865 to 2022. This article includes descriptions of how to implement these spherical Bessel functions and their multi-branched real inverses.

Keywords

Cite

@article{arxiv.2207.00707,
  title  = {Inverse spherical Bessel functions generalize Lambert W and solve similar equations containing trigonometric or hyperbolic subexpressions or their inverses},
  author = {David R. Stoutemyer},
  journal= {arXiv preprint arXiv:2207.00707},
  year   = {2022}
}

Comments

29 pages, 13 figures, 6 tables