11.9 Lommel Functions11.11 Asymptotic Expansions of Anger–Weber Functions

§11.10 Anger–Weber Functions

Contents

§11.10(i) Definitions

The Anger function \mathop{\mathbf{J}_{{\nu}}\/}\nolimits\!\left(z\right) and Weber function \mathop{\mathbf{E}_{{\nu}}\/}\nolimits\!\left(z\right) are defined by

11.10.1\mathop{\mathbf{J}_{{\nu}}\/}\nolimits\!\left(z\right)=\frac{1}{\pi}\int _{0}^{\pi}\mathop{\cos\/}\nolimits\!\left(\nu\theta-z\mathop{\sin\/}\nolimits\theta\right)d\theta,
11.10.2\mathop{\mathbf{E}_{{\nu}}\/}\nolimits\!\left(z\right)=\frac{1}{\pi}\int _{0}^{\pi}\mathop{\sin\/}\nolimits\!\left(\nu\theta-z\mathop{\sin\/}\nolimits\theta\right)d\theta.

Each is an entire function of z and \nu. Also,

11.10.3\frac{1}{\pi}\int _{0}^{{2\pi}}\mathop{\cos\/}\nolimits\!\left(\nu\theta-z\mathop{\sin\/}\nolimits\theta\right)d\theta=(1+\mathop{\cos\/}\nolimits\!\left(2\pi\nu\right))\,\mathop{\mathbf{J}_{{\nu}}\/}\nolimits\!\left(z\right)+\mathop{\sin\/}\nolimits\!\left(2\pi\nu\right)\mathop{\mathbf{E}_{{\nu}}\/}\nolimits\!\left(z\right).

The associated Anger–Weber function \mathop{\mathbf{A}_{{\nu}}\/}\nolimits\!\left(z\right) is defined by

11.10.4\mathop{\mathbf{A}_{{\nu}}\/}\nolimits\!\left(z\right)=\frac{1}{\pi}\int _{0}^{\infty}e^{{-\nu t-z\mathop{\sinh\/}\nolimits t}}dt,\realpart{z}>0.

(11.10.4) also applies when \realpart{z}=0 and \realpart{\nu}>0.

§11.10(ii) Differential Equations

The Anger and Weber functions satisfy the inhomogeneous Bessel differential equation

11.10.5\frac{{d}^{2}w}{{dz}^{2}}+\frac{1}{z}\frac{dw}{dz}+\left(1-\frac{\nu^{2}}{z^{2}}\right)w=f(\nu,z),

where

11.10.6f(\nu,z)=\frac{(z-\nu)}{\pi z^{2}}\mathop{\sin\/}\nolimits\!\left(\pi\nu\right),w=\mathop{\mathbf{J}_{{\nu}}\/}\nolimits\!\left(z\right),

or

11.10.7f(\nu,z)=-\frac{1}{\pi z^{2}}(z+\nu+(z-\nu)\mathop{\cos\/}\nolimits\!\left(\pi\nu\right)),w=\mathop{\mathbf{E}_{{\nu}}\/}\nolimits\!\left(z\right).

§11.10(iii) Maclaurin Series

§11.10(iv) Graphics

See accompanying text
Figure 11.10.1: Anger function \mathop{\mathbf{J}_{{\nu}}\/}\nolimits\!\left(x\right) for -8\leq x\leq 8 and \nu=0,\frac{1}{2},1,\frac{3}{2}. Magnify
See accompanying text
Figure 11.10.2: Weber function \mathop{\mathbf{E}_{{\nu}}\/}\nolimits\!\left(x\right) for -8\leq x\leq 8 and \nu=0,\frac{1}{2},1,\frac{3}{2}. Magnify
Figure 11.10.3: Anger function \mathop{\mathbf{J}_{{\nu}}\/}\nolimits\!\left(x\right) for -10\leq x\leq 10 and 0\leq\nu\leq 5. Magnify
Figure 11.10.4: Weber function \mathop{\mathbf{E}_{{\nu}}\/}\nolimits\!\left(x\right) for -10\leq x\leq 10 and 0\leq\nu\leq 5. Magnify

§11.10(v) Interrelations

§11.10(vi) Relations to Other Functions

For n=1,2,3,\dots,

11.10.22\mathop{\mathbf{E}_{{n}}\/}\nolimits\!\left(z\right)=-\mathop{\mathbf{H}_{{n}}\/}\nolimits\!\left(z\right)+\frac{1}{\pi}\sum _{{k=0}}^{{m_{1}}}\frac{\mathop{\Gamma\/}\nolimits\!\left(k+\tfrac{1}{2}\right)}{\mathop{\Gamma\/}\nolimits\!\left(n\!+\!\tfrac{1}{2}\!-\! k\right)}(\tfrac{1}{2}z)^{{n-2k-1}},

and

11.10.23\mathop{\mathbf{E}_{{-n}}\/}\nolimits\!\left(z\right)=-\mathop{\mathbf{H}_{{-n}}\/}\nolimits\!\left(z\right)+\frac{(-1)^{{n+1}}}{\pi}\sum _{{k=0}}^{{m_{2}}}\frac{\mathop{\Gamma\/}\nolimits\!\left(n\!-\! k\!-\!\tfrac{1}{2}\right)}{\mathop{\Gamma\/}\nolimits\!\left(k+\tfrac{3}{2}\right)}(\tfrac{1}{2}z)^{{-n+2k+1}},

where

11.10.24
m_{1}=\left\lfloor\tfrac{1}{2}n-\tfrac{1}{2}\right\rfloor,
m_{2}=\left\lceil\tfrac{1}{2}n-\tfrac{3}{2}\right\rceil.

§11.10(vii) Special Values

§11.10(viii) Expansions in Series of Products of Bessel Functions

§11.10(x) Integrals and Sums

For collections of integral representations and integrals see Erdélyi et al. (1954a, §§4.19 and 5.17), Marichev (1983, pp. 194–195 and 214–215), Oberhettinger (1972, p. 128), Oberhettinger (1974, §§1.12 and 2.7), Oberhettinger (1990, pp. 105 and 189–190), Prudnikov et al. (1990, §§1.5 and 2.8), Prudnikov et al. (1992a, §3.18), Prudnikov et al. (1992b, §3.18), and Zanovello (1977).

For sums see Hansen (1975, pp. 456–457) and Prudnikov et al. (1990, §§6.4.2–6.4.3).

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