14.2 Differential Equations14.4 Graphics

§14.3 Definitions and Hypergeometric Representations

Contents

§14.3(i) Interval -1<x<1

The following are real-valued solutions of (14.2.2) when \mu, \nu\in\Real and x\in(-1,1).

Ferrers Function of the First Kind

14.3.1\mathop{\mathsf{P}^{{\mu}}_{{\nu}}\/}\nolimits\!\left(x\right)=\left(\frac{1+x}{1-x}\right)^{{\mu/2}}\mathop{\mathbf{F}\/}\nolimits\!\left(\nu+1,-\nu;1-\mu;\tfrac{1}{2}-\tfrac{1}{2}x\right).

Ferrers Function of the Second Kind

14.3.2\mathop{\mathsf{Q}^{{\mu}}_{{\nu}}\/}\nolimits\!\left(x\right)=\frac{\pi}{2\mathop{\sin\/}\nolimits\!\left(\mu\pi\right)}\left(\mathop{\cos\/}\nolimits\!\left(\mu\pi\right)\left(\frac{1+x}{1-x}\right)^{{\mu/2}}\mathop{\mathbf{F}\/}\nolimits\!\left(\nu+1,-\nu;1-\mu;\tfrac{1}{2}-\tfrac{1}{2}x\right)-\frac{\mathop{\Gamma\/}\nolimits\!\left(\nu+\mu+1\right)}{\mathop{\Gamma\/}\nolimits\!\left(\nu-\mu+1\right)}\left(\frac{1-x}{1+x}\right)^{{\mu/2}}\mathop{\mathbf{F}\/}\nolimits\!\left(\nu+1,-\nu;1+\mu;\tfrac{1}{2}-\tfrac{1}{2}x\right)\right).

Here and elsewhere in this chapter

14.3.3\mathop{\mathbf{F}\/}\nolimits\!\left(a,b;c;x\right)=\frac{1}{\mathop{\Gamma\/}\nolimits\!\left(c\right)}\mathop{F\/}\nolimits\!\left(a,b;c;x\right)

is Olver’s hypergeometric function (§15.1).

\mathop{\mathsf{P}^{{\mu}}_{{\nu}}\/}\nolimits\!\left(x\right) exists for all values of \mu and \nu. \mathop{\mathsf{Q}^{{\mu}}_{{\nu}}\/}\nolimits\!\left(x\right) is undefined when \mu+\nu=-1,-2,-3,\dots.

When \mu=m=0,1,2,\ldots, (14.3.1) reduces to

14.3.4\mathop{\mathsf{P}^{{m}}_{{\nu}}\/}\nolimits\!\left(x\right)=(-1)^{m}\frac{\mathop{\Gamma\/}\nolimits\!\left(\nu+m+1\right)}{2^{m}\mathop{\Gamma\/}\nolimits\!\left(\nu-m+1\right)}\left(1-x^{2}\right)^{{m/2}}\mathop{\mathbf{F}\/}\nolimits\!\left(\nu+m+1,m-\nu;m+1;\tfrac{1}{2}-\tfrac{1}{2}x\right);

equivalently,

14.3.5\mathop{\mathsf{P}^{{m}}_{{\nu}}\/}\nolimits\!\left(x\right)=(-1)^{m}\frac{\mathop{\Gamma\/}\nolimits\!\left(\nu+m+1\right)}{\mathop{\Gamma\/}\nolimits\!\left(\nu-m+1\right)}\left(\frac{1-x}{1+x}\right)^{{m/2}}\mathop{\mathbf{F}\/}\nolimits\!\left(\nu+1,-\nu;m+1;\tfrac{1}{2}-\tfrac{1}{2}x\right).

When \mu=m (\in\Integer) (14.3.2) is replaced by its limiting value; see Hobson (1931, §132) for details. See also (14.3.12)–(14.3.14) for this case.

§14.3(ii) Interval 1<x<\infty

Associated Legendre Function of the First Kind

14.3.6\mathop{P^{{\mu}}_{{\nu}}\/}\nolimits\!\left(x\right)=\left(\frac{x+1}{x-1}\right)^{{\mu/2}}\mathop{\mathbf{F}\/}\nolimits\!\left(\nu+1,-\nu;1-\mu;\tfrac{1}{2}-\tfrac{1}{2}x\right).

Associated Legendre Function of the Second Kind

14.3.7\mathop{Q^{{\mu}}_{{\nu}}\/}\nolimits\!\left(x\right)=e^{{\mu\pi i}}\frac{\pi^{{1/2}}\mathop{\Gamma\/}\nolimits\!\left(\nu+\mu+1\right)\left(x^{2}-1\right)^{{\mu/2}}}{2^{{\nu+1}}x^{{\nu+\mu+1}}}\mathop{\mathbf{F}\/}\nolimits\!\left(\tfrac{1}{2}\nu+\tfrac{1}{2}\mu+1,\tfrac{1}{2}\nu+\tfrac{1}{2}\mu+\tfrac{1}{2};\nu+\tfrac{3}{2};\frac{1}{x^{2}}\right),\mu+\nu\neq-1,-2,-3,\dots.

As standard solutions of (14.2.2) we take the pair \mathop{P^{{-\mu}}_{{\nu}}\/}\nolimits\!\left(x\right) and \mathop{\boldsymbol{Q}^{{\mu}}_{{\nu}}\/}\nolimits\!\left(x\right), where

14.3.9\mathop{P^{{-\mu}}_{{\nu}}\/}\nolimits\!\left(x\right)=\left(\frac{x-1}{x+1}\right)^{{\mu/2}}\mathop{\mathbf{F}\/}\nolimits\!\left(\nu+1,-\nu;\mu+1;\tfrac{1}{2}-\tfrac{1}{2}x\right),

and

14.3.10\mathop{\boldsymbol{Q}^{{\mu}}_{{\nu}}\/}\nolimits\!\left(x\right)=e^{{-\mu\pi i}}\frac{\mathop{Q^{{\mu}}_{{\nu}}\/}\nolimits\!\left(x\right)}{\mathop{\Gamma\/}\nolimits\!\left(\nu+\mu+1\right)}.

Like \mathop{P^{{\mu}}_{{\nu}}\/}\nolimits\!\left(x\right), but unlike \mathop{Q^{{\mu}}_{{\nu}}\/}\nolimits\!\left(x\right), \mathop{\boldsymbol{Q}^{{\mu}}_{{\nu}}\/}\nolimits\!\left(x\right) is real-valued when \nu, \mu\in\Real and x\in(1,\infty), and is defined for all values of \nu and \mu. The notation \mathop{\boldsymbol{Q}^{{\mu}}_{{\nu}}\/}\nolimits\!\left(x\right) is due to Olver (1997b, pp. 170 and 178).

§14.3(iii) Alternative Hypergeometric Representations

where

14.3.15\mathop{P^{{-\mu}}_{{\nu}}\/}\nolimits\!\left(x\right)=2^{{-\mu}}\left(x^{2}-1\right)^{{\mu/2}}\mathop{\mathbf{F}\/}\nolimits\!\left(\mu-\nu,\nu+\mu+1;\mu+1;\tfrac{1}{2}-\tfrac{1}{2}x\right),
14.3.16\mathop{\cos\/}\nolimits\!\left(\nu\pi\right)\mathop{P^{{-\mu}}_{{\nu}}\/}\nolimits\!\left(x\right)=\frac{2^{{\nu}}\pi^{{1/2}}x^{{\nu-\mu}}\left(x^{2}-1\right)^{{\mu/2}}}{\mathop{\Gamma\/}\nolimits\!\left(\nu+\mu+1\right)}\mathop{\mathbf{F}\/}\nolimits\!\left(\tfrac{1}{2}\mu-\tfrac{1}{2}\nu,\tfrac{1}{2}\mu-\tfrac{1}{2}\nu+\tfrac{1}{2};\tfrac{1}{2}-\nu;\frac{1}{x^{2}}\right)-\frac{\pi^{{1/2}}\left(x^{2}-1\right)^{{\mu/2}}}{2^{{\nu+1}}\mathop{\Gamma\/}\nolimits\!\left(\mu-\nu\right)x^{{\nu+\mu+1}}}\mathop{\mathbf{F}\/}\nolimits\!\left(\tfrac{1}{2}\nu+\tfrac{1}{2}\mu+1,\tfrac{1}{2}\nu+\tfrac{1}{2}\mu+\tfrac{1}{2};\nu+\tfrac{3}{2};\frac{1}{x^{2}}\right),
14.3.17\mathop{P^{{-\mu}}_{{\nu}}\/}\nolimits\!\left(x\right)=\frac{\pi\left(x^{2}-1\right)^{{\mu/2}}}{2^{{\mu}}}\left(\frac{\mathop{\mathbf{F}\/}\nolimits\!\left(\frac{1}{2}\mu-\frac{1}{2}\nu,\frac{1}{2}\nu+\frac{1}{2}\mu+\frac{1}{2};\frac{1}{2};x^{2}\right)}{\mathop{\Gamma\/}\nolimits\!\left(\frac{1}{2}\mu-\frac{1}{2}\nu+\frac{1}{2}\right)\mathop{\Gamma\/}\nolimits\!\left(\frac{1}{2}\nu+\frac{1}{2}\mu+1\right)}-\frac{x\mathop{\mathbf{F}\/}\nolimits\!\left(\frac{1}{2}\mu-\frac{1}{2}\nu+\frac{1}{2},\frac{1}{2}\nu+\frac{1}{2}\mu+1;\frac{3}{2};x^{2}\right)}{\mathop{\Gamma\/}\nolimits\!\left(\frac{1}{2}\mu-\frac{1}{2}\nu\right)\mathop{\Gamma\/}\nolimits\!\left(\frac{1}{2}\nu+\frac{1}{2}\mu+\frac{1}{2}\right)}\right),
14.3.20\frac{2\mathop{\sin\/}\nolimits\!\left(\mu\pi\right)}{\pi}\mathop{\boldsymbol{Q}^{{\mu}}_{{\nu}}\/}\nolimits\!\left(x\right)=\frac{(x+1)^{{\mu/2}}}{\mathop{\Gamma\/}\nolimits\!\left(\nu+\mu+1\right)(x-1)^{{\mu/2}}}\mathop{\mathbf{F}\/}\nolimits\!\left(\nu+1,-\nu;1-\mu;\tfrac{1}{2}-\tfrac{1}{2}x\right)-\frac{(x-1)^{{\mu/2}}}{\mathop{\Gamma\/}\nolimits\!\left(\nu-\mu+1\right)(x+1)^{{\mu/2}}}\mathop{\mathbf{F}\/}\nolimits\!\left(\nu+1,-\nu;\mu+1;\tfrac{1}{2}-\tfrac{1}{2}x\right).

For further hypergeometric representations of \mathop{P^{{\mu}}_{{\nu}}\/}\nolimits\!\left(x\right) and \mathop{Q^{{\mu}}_{{\nu}}\/}\nolimits\!\left(x\right) see Erdélyi et al. (1953a, pp. 123–139), Andrews et al. (1999, §3.1), Magnus et al. (1966, pp. 153–163), and §15.8(iii).