About the Project
10 Bessel FunctionsSpherical Bessel Functions

§10.47 Definitions and Basic Properties

Contents
  1. §10.47(i) Differential Equations
  2. §10.47(ii) Standard Solutions
  3. §10.47(iii) Numerically Satisfactory Pairs of Solutions
  4. §10.47(iv) Interrelations
  5. §10.47(v) Reflection Formulas

§10.47(i) Differential Equations

10.47.1 z^{2}\frac{{\mathrm{d}}^{2}w}{{\mathrm{d}z}^{2}}+2z\frac{\mathrm{d}w}{\mathrm{%
d}z}+\left(z^{2}-n(n+1)\right)w=0,
10.47.2 z^{2}\frac{{\mathrm{d}}^{2}w}{{\mathrm{d}z}^{2}}+2z\frac{\mathrm{d}w}{\mathrm{%
d}z}-\left(z^{2}+n(n+1)\right)w=0.

Here, and throughout the remainder of §§10.4710.60, nis a nonnegative integer. (This is in contrast to other treatments of spherical Bessel functions, including Abramowitz and Stegun (1964, Chapter 10), in which n can be any integer. However, there is a gain in symmetry, without any loss of generality in applications, on restricting n\geq 0.)

Equations (10.47.1) and (10.47.2) each have a regular singularity at z=0 with indices n, -n-1, and an irregular singularity at z=\infty of rank 1; compare §§2.7(i)2.7(ii).

§10.47(ii) Standard Solutions

Equation (10.47.1)

10.47.4 \mathsf{y}_{n}\left(z\right)=\sqrt{\tfrac{1}{2}\pi/z}Y_{n+\frac{1}{2}}\left(z%
\right)=(-1)^{n+1}\sqrt{\tfrac{1}{2}\pi/z}J_{-n-\frac{1}{2}}\left(z\right),
10.47.5 {\mathsf{h}^{(1)}_{n}}\left(z\right)=\sqrt{\tfrac{1}{2}\pi/z}{H^{(1)}_{n+\frac%
{1}{2}}}\left(z\right)=(-1)^{n+1}\mathrm{i}\sqrt{\tfrac{1}{2}\pi/z}{H^{(1)}_{-%
n-\frac{1}{2}}}\left(z\right),

\mathsf{j}_{n}\left(z\right) and \mathsf{y}_{n}\left(z\right) are the spherical Bessel functions of the first and second kinds, respectively; {\mathsf{h}^{(1)}_{n}}\left(z\right) and {\mathsf{h}^{(2)}_{n}}\left(z\right) are the spherical Bessel functions of the third kind.

Equation (10.47.2)

10.47.7 {\mathsf{i}^{(1)}_{n}}\left(z\right)=\sqrt{\tfrac{1}{2}\pi/z}I_{n+\frac{1}{2}}%
\left(z\right)
10.47.8 {\mathsf{i}^{(2)}_{n}}\left(z\right)=\sqrt{\tfrac{1}{2}\pi/z}I_{-n-\frac{1}{2}%
}\left(z\right)

{\mathsf{i}^{(1)}_{n}}\left(z\right), {\mathsf{i}^{(2)}_{n}}\left(z\right), and \mathsf{k}_{n}\left(z\right) are the modified spherical Bessel functions.

Many properties of \mathsf{j}_{n}\left(z\right), \mathsf{y}_{n}\left(z\right), {\mathsf{h}^{(1)}_{n}}\left(z\right), {\mathsf{h}^{(2)}_{n}}\left(z\right), {\mathsf{i}^{(1)}_{n}}\left(z\right), {\mathsf{i}^{(2)}_{n}}\left(z\right), and \mathsf{k}_{n}\left(z\right) follow straightforwardly from the above definitions and results given in preceding sections of this chapter. For example, z^{-n}\mathsf{j}_{n}\left(z\right), z^{n+1}\mathsf{y}_{n}\left(z\right), z^{n+1}{\mathsf{h}^{(1)}_{n}}\left(z\right), z^{n+1}{\mathsf{h}^{(2)}_{n}}\left(z\right), z^{-n}{\mathsf{i}^{(1)}_{n}}\left(z\right), z^{n+1}{\mathsf{i}^{(2)}_{n}}\left(z\right), and z^{n+1}\mathsf{k}_{n}\left(z\right) are all entire functions of z.

§10.47(iii) Numerically Satisfactory Pairs of Solutions

For (10.47.1) numerically satisfactory pairs of solutions are given by Table 10.2.1 with the symbols J, Y, H, and \nu replaced by \mathsf{j}, \mathsf{y}, \mathsf{h}, and n, respectively.

For (10.47.2) numerically satisfactory pairs of solutions are {\mathsf{i}^{(1)}_{n}}\left(z\right) and \mathsf{k}_{n}\left(z\right) in the right half of the z-plane, and {\mathsf{i}^{(1)}_{n}}\left(z\right) and \mathsf{k}_{n}\left(-z\right) in the left half of the z-plane.

§10.47(iv) Interrelations

§10.47(v) Reflection Formulas