36.1 Special Notation36.3 Visualizations of Canonical Integrals

§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

36.2.2\mathop{\Phi^{{(\mathrm{E})}}\/}\nolimits\!\left(s,t;\mathbf{x}\right)=s^{3}-3st^{2}+z(s^{2}+t^{2})+yt+xs,\mathbf{x}=\{ x,y,z\},

(elliptic umbilic).

36.2.3\mathop{\Phi^{{(\mathrm{H})}}\/}\nolimits\!\left(s,t;\mathbf{x}\right)=s^{3}+t^{3}+zst+yt+xs,\mathbf{x}=\{ x,y,z\},

(hyperbolic umbilic).

Canonical Integrals

36.2.4\mathop{\Psi _{{K}}\/}\nolimits\!\left(\mathbf{x}\right)=\int _{{-\infty}}^{\infty}\mathop{\exp\/}\nolimits\!\left(i\mathop{\Phi _{{K}}\/}\nolimits\!\left(t;\mathbf{x}\right)\right)dt.
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}.
36.2.6\mathop{\Psi^{{(\mathrm{E})}}\/}\nolimits\!\left(\mathbf{x}\right)=2\sqrt{\ifrac{\pi}{3}}\,\mathop{\exp\/}\nolimits\!\left(i\left(\tfrac{4}{27}z^{3}+\tfrac{1}{3}xz-\tfrac{1}{4}\pi\right)\right)\int _{{\infty\mathop{\exp\/}\nolimits\!\left(-7\pi i/12\right)}}^{{\infty\mathop{\exp\/}\nolimits\!\left(\pi i/12\right)}}\mathop{\exp\/}\nolimits\!\left(i\left(u^{6}+2zu^{4}+(z^{2}+x)u^{2}+\frac{y^{2}}{12u^{2}}\right)\right)du,

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

36.2.7
\mathop{\Psi^{{(\mathrm{E})}}\/}\nolimits\!\left(\mathbf{x}\right)=\dfrac{4\pi}{3^{{1/3}}}\mathop{\exp\/}\nolimits\!\left(i\left(\tfrac{2}{27}z^{3}-\tfrac{1}{3}xz\right)\right)\left(\mathop{\exp\/}\nolimits\!\left(-i\dfrac{\pi}{6}\right)\mathrm{F}_{{+}}(\mathbf{x})+\mathop{\exp\/}\nolimits\!\left(i\dfrac{\pi}{6}\right)\mathrm{F}_{{-}}(\mathbf{x})\right),
\mathrm{F}_{{\pm}}(\mathbf{x})=\int _{0}^{\infty}\mathop{\cos\/}\nolimits\!\left(ry\mathop{\exp\/}\nolimits\!\left(\pm i\dfrac{\pi}{6}\right)\right)\mathop{\exp\/}\nolimits\!\left(2ir^{2}z\mathop{\exp\/}\nolimits\!\left(\pm i\dfrac{\pi}{3}\right)\right)\mathop{\mathrm{Ai}\/}\nolimits\!\left(3^{{2/3}}r^{2}+3^{{-1/3}}\mathop{\exp\/}\nolimits\!\left(\mp i\dfrac{\pi}{3}\right)\left(\tfrac{1}{3}z^{2}-x\right)\right)dr.
36.2.8\mathop{\Psi^{{(\mathrm{H})}}\/}\nolimits\!\left(\mathbf{x}\right)=4\sqrt{\ifrac{\pi}{6}}\,\mathop{\exp\/}\nolimits\!\left(i\left(\tfrac{1}{27}z^{3}+\tfrac{1}{6}z(y+x)+\tfrac{1}{4}\pi\right)\right)\*\int _{{\infty\mathop{\exp\/}\nolimits\!\left(5\pi i/12\right)}}^{{\infty\mathop{\exp\/}\nolimits\!\left(\pi i/12\right)}}\mathop{\exp\/}\nolimits\!\left(i\left(2u^{6}+2zu^{4}+\left(\tfrac{1}{2}z^{2}+x+y\right)u^{2}-\frac{(y-x)^{2}}{24u^{2}}\right)\right)du,

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

36.2.9\mathop{\Psi^{{(\mathrm{H})}}\/}\nolimits\!\left(\mathbf{x}\right)=\frac{2\pi}{3^{{1/3}}}\int _{{\infty\mathop{\exp\/}\nolimits\!\left(5\pi i/6\right)}}^{{\infty\mathop{\exp\/}\nolimits\!\left(\pi i/6\right)}}\mathop{\exp\/}\nolimits\!\left(i(s^{3}+xs)\right)\mathop{\mathrm{Ai}\/}\nolimits\!\left(\frac{zs+y}{3^{{1/3}}}\right)ds.

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)):

36.2.14\mathop{\Psi _{{2}}\/}\nolimits\!\left(\mathbf{x}\right)=P(x_{2},x_{1})=\int _{{-\infty}}^{\infty}\mathop{\exp\/}\nolimits\!\left(i(t^{4}+x_{2}t^{2}+x_{1}t)\right)dt.

(Other notations also appear in the literature.)

36.2.15\mathop{\Psi _{{K}}\/}\nolimits\!\left(\boldsymbol{{0}}\right)=\frac{2}{K+2}\mathop{\Gamma\/}\nolimits\!\left(\frac{1}{K+2}\right)\*\begin{cases}\mathop{\exp\/}\nolimits\!\left(i\dfrac{\pi}{2(K+2)}\right),&K\text{ even,}\\
\mathop{\cos\/}\nolimits\!\left(\dfrac{\pi}{2(K+2)}\right),&K\text{ odd}.\end{cases}
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\, 0.48022.

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.