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36 Integrals with Coalescing SaddlesProperties

§36.2 Catastrophes and Canonical Integrals

Contents

§36.2(i) Definitions

Normal Forms Associated with Canonical Integrals: Cuspoid Catastrophe with Codimension K

36.2.1\mathop{\Phi_{{K}}\/}\nolimits\!\left(t;\mathbf{x}\right)=t^{{K+2}}+\sum_{{m=1%
}}^{K}x_{m}t^{m}.

Special cases: K=1, fold catastrophe; K=2, cusp catastrophe; K=3, swallowtail catastrophe.

Normal Forms for Umbilic Catastrophes with Codimension K=3

(elliptic umbilic).

(hyperbolic umbilic).

Canonical Integrals

36.2.5\mathop{\Psi^{{(\mathrm{U})}}\/}\nolimits\!\left(\mathbf{x}\right)=\int_{{-%
\infty}}^{\infty}\int_{{-\infty}}^{\infty}\mathop{\exp\/}\nolimits\!\left(i%
\mathop{\Phi^{{(\mathrm{U})}}\/}\nolimits\!\left(s,t;\mathbf{x}\right)\right)dsdt,\mathrm{U}=\mathrm{E},\mathrm{H}.

with the contour passing to the lower right of u=0.

with the contour passing to the upper right of u=0.

Diffraction Catastrophes

36.2.10\mathop{\Psi_{{K}}\/}\nolimits\!(\mathbf{x};k)=\sqrt{k}\int_{{-\infty}}^{%
\infty}\mathop{\exp\/}\nolimits\!\left(ik\mathop{\Phi_{{K}}\/}\nolimits\!\left%
(t;\mathbf{x}\right)\right)dt,k>0.
36.2.11\mathop{\Psi^{{(\mathrm{U})}}\/}\nolimits\!(\mathbf{x};k)=k\int_{{-\infty}}^{%
\infty}\int_{{-\infty}}^{\infty}\mathop{\exp\/}\nolimits\!\left(ik\mathop{\Phi%
^{{(\mathrm{U})}}\/}\nolimits\!\left(s,t;\mathbf{x}\right)\right)dsdt,\mathrm{U=E,H}; k>0.

For more extensive lists of normal forms of catastrophes (umbilic and beyond) involving two variables (“corank two”) see Arnol’d (1972, 1974, 1975).

§36.2(ii) Special Cases

36.2.12\mathop{\Psi_{{0}}\/}\nolimits=\sqrt{\pi}\mathop{\exp\/}\nolimits\!\left(i%
\frac{\pi}{4}\right).

\mathop{\Psi_{{1}}\/}\nolimits is related to the Airy function (§9.2):

36.2.13\mathop{\Psi_{{1}}\/}\nolimits\!\left(x\right)=\frac{2\pi}{3^{{1/3}}}\mathop{%
\mathrm{Ai}\/}\nolimits\!\left(\frac{x}{3^{{1/3}}}\right).

\mathop{\Psi_{{2}}\/}\nolimits is the Pearcey integral (Pearcey (1946)):

(Other notations also appear in the literature.)

36.2.16
\mathop{\Psi_{{1}}\/}\nolimits\!\left(\boldsymbol{{0}}\right)=1.54669,
\mathop{\Psi_{{2}}\/}\nolimits\!\left(\boldsymbol{{0}}\right)=1.67481+i\,0.69373
\mathop{\Psi_{{3}}\/}\nolimits\!\left(\boldsymbol{{0}}\right)=1.74646,
\mathop{\Psi_{{4}}\/}\nolimits\!\left(\boldsymbol{{0}}\right)=1.79222+i\,0.480%
22.

Addendum: For further special cases see §36.2(iv)

§36.2(iii) Symmetries

§36.2(iv) Addendum to 36.2(ii) Special Cases

36.2.28\mathop{\Psi^{{(\mathrm{E})}}\/}\nolimits\!\left(0,0,z\right)={\Psi^{{\ast}}}^%
{{(\mathrm{E})}}(0,0,-z)\\
=2\pi\sqrt{\frac{\pi z}{27}}\mathop{\exp\/}\nolimits\!\left(\frac{2}{27}iz^{3}%
\right)\*\left(\mathop{J_{{-1/6}}\/}\nolimits\!\left(\frac{2}{27}z^{3}\right)+%
i\mathop{J_{{1/6}}\/}\nolimits\!\left(\frac{2}{27}z^{3}\right)\right),z\geq 0,
36.2.29\mathop{\Psi^{{(\mathrm{H})}}\/}\nolimits\!\left(0,0,z\right)={\Psi^{{\ast}}}^%
{{(\mathrm{H})}}(0,0,-z)=\frac{2^{{1/3}}}{\sqrt{3}}\mathop{\exp\/}\nolimits\!%
\left(\frac{1}{27}iz^{3}\right)\mathop{\Psi^{{(\mathrm{E})}}\/}\nolimits\!%
\left(0,0,-\frac{z}{2^{{2/3}}}\right),-\infty<z<\infty.

Here the functions {\Psi^{{\ast}}}^{{(\mathrm{E})}} and {\Psi^{{\ast}}}^{{(\mathrm{H})}} are the complex conjugates of the functions \mathop{\Psi^{{(\mathrm{E})}}\/}\nolimits and \mathop{\Psi^{{(\mathrm{H})}}\/}\nolimits, respectively.