§9.12 Scorer Functions§9.14 Incomplete Airy Functions

§ 9.13. Generalized Airy Functions

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Contents

§ 9.13(i). Generalizations from the Differential Equation

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Equations of the form

9.13.1 \frac{{d}^{2}w}{{dz}^{2}}=z^{n}w, n=1,2,3,\ldots,
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Defines:
n: parameter
Symbols:
z: complex variable and w: function
Referenced by:
§9.13(i), §9.13(i), §9.13(i)
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are used in approximating solutions to differential equations with multiple turning points; see §2.8(v). The general solution of (9.13.1) is given by

9.13.2 w=z^{{1/2}}\mathscr{Z}_{{p}}\!\left(\zeta\right),
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Defines:
w: function
Symbols:
z: complex variable, p: variable and \zeta: variable
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where

9.13.3
p=\frac{1}{n+2},
\zeta=\frac{2}{n+2}z^{{(n+2)/2}}=2pz^{{1/(2p)}},
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Defines:
p: variable and \zeta: variable
Symbols:
z: complex variable and n: parameter
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and \mathscr{Z}_{{p}} is any linear combination of the modified Bessel functions I_{{p}} and e^{{p\pi i}}K_{{p}}Ch.10).

Swanson and Headley (1967) define independent solutions A_{{n}}\!\left(z\right) and B_{{n}}\!\left(z\right) of (9.13.1) by

9.13.4
A_{{n}}\!\left(z\right)=(2p/\pi)\sin\!\left(p\pi\right)z^{{1/2}}K_{{p}}\!\left(\zeta\right),
B_{{n}}\!\left(z\right)=(pz)^{{1/2}}\left(I_{{-p}}\!\left(\zeta\right)+I_{{p}}\!\left(\zeta\right)\right),
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Defines:
A_{{n}}\!\left(z\right): generalized (ODE) Airy function and B_{{n}}\!\left(z\right): generalized (ODE) Airy function
Symbols:
z: complex variable, n: parameter, p: variable and \zeta: variable
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when z is real and positive, and by analytic continuation elsewhere. (All solutions of (9.13.1) are entire functions of z.) When n=1, A_{{n}}\!\left(z\right) and B_{{n}}\!\left(z\right) become \mathrm{Ai}\!\left(z\right) and \mathrm{Bi}\!\left(z\right), respectively.

Properties of A_{{n}}\!\left(z\right) and B_{{n}}\!\left(z\right) follow from the corresponding properties of the modified Bessel functions. They include:

9.13.5
A_{{n}}\!\left(0\right)=p^{{1/2}}B_{{n}}\!\left(0\right)=\frac{p^{{1-p}}}{\Gamma\!\left(1-p\right)},
-{{A_{{n}}}^{{\prime}}}\!\left(0\right)=p^{{1/2}}{{B_{{n}}}^{{\prime}}}\!\left(0\right)=\frac{p^{p}}{\Gamma\!\left(p\right)}.
9.13.6 A_{{n}}\!\left(-z\right)=\begin{cases}pz^{{1/2}}\left(J_{{-p}}\!\left(\zeta\right)+J_{{p}}\!\left(\zeta\right)\right),&n\text{ odd},\\
p^{{1/2}}B_{{n}}\!\left(z\right),&n\text{ even},\end{cases}
9.13.7 B_{{n}}\!\left(-z\right)=\begin{cases}(pz)^{{1/2}}\left(J_{{-p}}\!\left(\zeta\right)-J_{{p}}\!\left(\zeta\right)\right),&n\text{ odd},\\
p^{{-1/2}}A_{{n}}\!\left(z\right),&n\text{ even}.\end{cases}
9.13.8 \mathscr{W}\left\{ A_{{n}}\!\left(z\right),B_{{n}}\!\left(z\right)\right\}=\frac{2}{\pi}p^{{1/2}}\sin\!\left(p\pi\right).

The distribution in \Complex and asymptotic properties of the zeros of A_{{n}}\!\left(z\right), {{A_{{n}}}^{{\prime}}}\!\left(z\right), B_{{n}}\!\left(z\right), and {{B_{{n}}}^{{\prime}}}\!\left(z\right) are investigated in Swanson and Headley (1967) and Headley and Barwell (1975).

In Olver (1977b, 1978) a different normalization is used. In place of (9.13.1) we have

9.13.13 \frac{{d}^{2}w}{{dt}^{2}}=\tfrac{1}{4}m^{2}t^{{m-2}}w,
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Defines:
m: index
Symbols:
w: function
Referenced by:
§9.13(i), §9.13(i)
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where m=3,4,5,\ldots. For real variables the solutions of (9.13.13) are denoted by U_{m}(t), U_{m}(-t) when m is even, and by V_{m}(t), \overline{V}_{m}(t) when m is odd. (The overbar has nothing to do with complex conjugates.) Their relations to the functions A_{{n}}\!\left(z\right) and B_{{n}}\!\left(z\right) are given by

9.13.14
m=n+2=1/p,
t=(\tfrac{1}{2}m)^{{-2/m}}z=\zeta^{{2/m}},
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Defines:
m: index
Symbols:
z: complex variable, n: parameter, p: variable and \zeta: variable
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9.13.15 \sqrt{2\pi}\left(\tfrac{1}{2}m\right)^{{(m-1)/m}}\csc\!\left(\ifrac{\pi}{m}\right)A_{{n}}\!\left(z\right)=\begin{cases}U_{m}(t),&m\text{ even},\\
V_{m}(t),&m\text{ odd},\end{cases}
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Defines:
m: index and V_{m}: Olver's generalized Airy function
Symbols:
A_{{n}}\!\left(z\right): generalized (ODE) Airy function, z: complex variable, n: parameter and U_{i}: Smirnov's generalized Airy function
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9.13.16 \sqrt{\pi}\left(\tfrac{1}{2}m\right)^{{(m-2)/(2m)}}\csc\!\left(\ifrac{\pi}{m}\right)B_{{n}}\!\left(z\right)=\begin{cases}U_{m}(-t),&m\text{ even},\\
\overline{V}_{m}(t),&m\text{ odd}.\end{cases}
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Defines:
m: index and V_{m}: Olver's generalized Airy function
Symbols:
B_{{n}}\!\left(z\right): generalized (ODE) Airy function, z: complex variable, n: parameter and U_{i}: Smirnov's generalized Airy function
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Properties and graphs of U_{m}(t), V_{m}(t), \overline{V}_{m}(t) are included in Olver (1977b) together with properties and graphs of real solutions of the equation

9.13.17 \frac{{d}^{2}w}{{dt}^{2}}=-\tfrac{1}{4}m^{2}t^{{m-2}}w, m even,
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Defines:
W_{m}: function
Symbols:
w: function and m: index
Referenced by:
§9.13(i)
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which are denoted by W_{m}(t), W_{m}(-t).

In \Complex, the solutions of (9.13.13) used in Olver (1978) are

9.13.18 w=U_{m}(te^{{-2j\pi i/m}}), j=0,\pm 1,\pm 2,\ldots.
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Defines:
j: index
Symbols:
U_{i}: Smirnov's generalized Airy function, w: function and m: index
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The function on the right-hand side is recessive in the sector -(2j-1)\pi/m\leq\mathrm{ph}z\leq(2j+1)\pi/m, and is therefore an essential member of any numerically satisfactory pair of solutions in this region.

Another normalization of (9.13.17) is used in Smirnov (1960), given by

9.13.19 \frac{{d}^{2}w}{{dx}^{2}}+x^{{\alpha}}w=0,
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Defines:
\alpha: parameter and x: parameter
Symbols:
w: function
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where \alpha>-2 and x>0. Solutions are w=U_{1}(x,\alpha), U_{2}(x,\alpha), where

9.13.20 U_{1}(x,\alpha)=\frac{1}{(\alpha+2)^{{1/(\alpha+2)}}}\*\Gamma\!\left(\frac{\alpha+1}{\alpha+2}\right)x^{{1/2}}J_{{-1/(\alpha+2)}}\!\left(\frac{2}{\alpha+2}x^{{(\alpha+2)/2}}\right),
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Defines:
U_{i}: Smirnov's generalized Airy function
Symbols:
\Gamma\!\left(z\right): Gamma function, \alpha: parameter and x: parameter
Referenced by:
§9.18(vii)
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9.13.21 U_{2}(x,\alpha)=(\alpha+2)^{{1/(\alpha+2)}}\*\Gamma\!\left(\frac{\alpha+3}{\alpha+2}\right)x^{{1/2}}J_{{1/(\alpha+2)}}\!\left(\frac{2}{\alpha+2}x^{{(\alpha+2)/2}}\right),
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Defines:
U_{i}: Smirnov's generalized Airy function
Symbols:
\Gamma\!\left(z\right): Gamma function, \alpha: parameter and x: parameter
Referenced by:
§9.18(vii)
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and J denotes the Bessel function (§Ch.10).

When \alpha is a positive integer the relation of these functions to W_{m}(t), W_{m}(-t) is as follows:

9.13.22
\alpha=m-2,
x=(m/2)^{{2/m}}t,
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Symbols:
\alpha: parameter, x: parameter and m: index
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9.13.23 U_{1}(x,\alpha)=\frac{\pi^{{1/2}}}{2^{{(m+2)/(2m)}}\Gamma\!\left(1/m\right)}\left(W_{m}(t)+W_{m}(-t)\right),
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Symbols:
\Gamma\!\left(z\right): Gamma function, \alpha: parameter, x: parameter, U_{i}: Smirnov's generalized Airy function, m: index and W_{m}: function
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9.13.24 U_{2}(x,\alpha)=\frac{\pi^{{1/2}}m^{{2/m}}}{2^{{(m+2)/(2m)}}\Gamma\!\left(-1/m\right)}\left(W_{m}(t){-}W_{m}(-t)\right).
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Symbols:
\Gamma\!\left(z\right): Gamma function, \alpha: parameter, x: parameter, U_{i}: Smirnov's generalized Airy function, m: index and W_{m}: function
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For properties of the zeros of the functions defined in this subsection see Laforgia and Muldoon (1988) and references given therein.

§ 9.13(ii). Generalizations from Integral Representations

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Reid (1972) and Drazin and Reid (1981, Appendix) introduce the following contour integrals in constructing approximate solutions to the Orr-Sommerfeld equation for fluid flow:

9.13.25 A_{{k}}\!\left(z,p\right)=\frac{1}{2\pi i}\int _{{\mathscr{L}_{k}}}t^{{-p}}\exp\!\left(zt-\tfrac{1}{3}t^{3}\right)dt, k=1,2,3, p\in\Complex,
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Defines:
A_{{k}}\!\left(z,p\right): generalized (integral) Airy function, k: index and p: parameter
Symbols:
z: complex variable and \mathscr{L}: integration path
Referenced by:
§9.13(ii)
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9.13.26 B_{{0}}\!\left(z,p\right)=\frac{1}{2\pi i}\int _{{\mathscr{L}_{0}}}t^{{-p}}\exp\!\left(zt-\tfrac{1}{3}t^{3}\right)dt, p=0,\pm 1,\pm 2,\ldots,
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Defines:
B_{{k}}\!\left(z,p\right): generalized (integral) Airy function
Symbols:
z: complex variable, p: parameter and \mathscr{L}: integration path
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9.13.27 B_{{k}}\!\left(z,p\right)=\int _{{\mathscr{I}_{k}}}t^{{-p}}\exp\!\left(zt-\tfrac{1}{3}t^{3}\right)dt, k=1,2,3, p=0,\pm 1,\pm 2,\ldots,
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Defines:
B_{{k}}\!\left(z,p\right): generalized (integral) Airy function
Symbols:
z: complex variable, k: index, p: parameter and \mathscr{I}: integration path
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with z\in\Complex in all cases. The integration paths \mathscr{L}_{0}, \mathscr{L}_{1}, \mathscr{L}_{2}, \mathscr{L}_{3} are depicted in Figure 9.13.1. \mathscr{I}_{1}, \mathscr{I}_{2}, \mathscr{I}_{3} are depicted in Figure 9.13.2. When p is not an integer the branch of t^{{-p}} in (9.13.25) is usually chosen to be \exp\!\left(-p(\ln|t|+i\mathrm{ph}t)\right) with 0\leq\mathrm{ph}t<2\pi.

See accompanying text
9.13.1. t-plane. Paths \mathscr{L}_{0}, \mathscr{L}_{1}, \mathscr{L}_{2}, \mathscr{L}_{3}.
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Defines:
\mathscr{L}: integration path
Referenced by:
§9.13(ii)
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See accompanying text
9.13.2. t-plane. Paths \mathscr{I}_{1}, \mathscr{I}_{2}, \mathscr{I}_{3}.
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Defines:
\mathscr{I}: integration path
Referenced by:
§9.13(ii)
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When p=0

9.13.28 A_{{1}}\!\left(z,0\right)=\mathrm{Ai}\!\left(z\right),
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Symbols:
\mathrm{Ai}\!\left(z\right): Airy function, A_{{k}}\!\left(z,p\right): generalized (integral) Airy function and z: complex variable
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9.13.29
A_{{2}}\!\left(z,0\right)=e^{{2\pi i/3}}\mathrm{Ai}\!\left(ze^{{2\pi i/3}}\right),
A_{{3}}\!\left(z,0\right)=e^{{-2\pi i/3}}\mathrm{Ai}\!\left(ze^{{-2\pi i/3}}\right),
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Symbols:
\mathrm{Ai}\!\left(z\right): Airy function, A_{{k}}\!\left(z,p\right): generalized (integral) Airy function and z: complex variable
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and

9.13.30
B_{{0}}\!\left(z,0\right)=0,
B_{{1}}\!\left(z,0\right)=\pi\mathrm{Hi}\!\left(z\right).
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Symbols:
B_{{k}}\!\left(z,p\right): generalized (integral) Airy function, \mathrm{Hi}\!\left(z\right): Scorer function and z: complex variable
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Each of the functions A_{{k}}\!\left(z,p\right) and B_{{k}}\!\left(z,p\right) satisfies the differential equation

9.13.31 \frac{{d}^{3}w}{{dz}^{3}}-z\frac{dw}{dz}+(p-1)w=0,
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Defines:
w: function
Symbols:
z: complex variable and p: parameter
Referenced by:
§9.13(ii)
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and the difference equation

9.13.32 f(p-3)-zf(p-1)+(p-1)f(p)=0.
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Defines:
f: function
Symbols:
z: complex variable and p: parameter
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The A_{{k}}\!\left(z,p\right) are related by

9.13.33
A_{{2}}\!\left(z,p\right)=e^{{-2(p-1)\pi i/3}}A_{{1}}\!\left(ze^{{2\pi i/3}},p\right),
A_{{3}}\!\left(z,p\right)=e^{{2(p-1)\pi i/3}}A_{{1}}\!\left(ze^{{-2\pi i/3}},p\right).
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Symbols:
A_{{k}}\!\left(z,p\right): generalized (integral) Airy function, z: complex variable and p: parameter
Permalink:
http://dlmf.nist.gov/9.13.E33
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Connection formulas for the solutions of (9.13.31) include

9.13.34 A_{{1}}\!\left(z,p\right)+A_{{2}}\!\left(z,p\right)+A_{{3}}\!\left(z,p\right)+B_{{0}}\!\left(z,p\right)=0,
9.13.35 B_{{2}}\!\left(z,p\right)-B_{{3}}\!\left(z,p\right)=2\pi iA_{{1}}\!\left(z,p\right),
9.13.36 B_{{3}}\!\left(z,p\right)-B_{{1}}\!\left(z,p\right)=2\pi iA_{{2}}\!\left(z,p\right),
9.13.37 B_{{1}}\!\left(z,p\right)-B_{{2}}\!\left(z,p\right)=2\pi iA_{{3}}\!\left(z,p\right).

Further properties of these functions, and also of similar contour integrals containing an additional factor (\ln t)^{q}, q=1,2,\ldots, in the integrand, are derived in Reid (1972), Drazin and Reid (1981, Appendix), and Baldwin (1985). These properties include Wronskians, asymptotic expansions, and information on zeros.

For further generalizations via integral representations see Chin and Hedstrom (1978), Janson et al. (1993, §10), and Kamimoto (1998).