A Catastrophe which can occur for three control factors and one behavior axis. The equations
References
Nordstrand, T. ``Swallowtail.''
http://www.uib.no/people/nfytn/stltxt.htm.
von Seggern, D. CRC Standard Curves and Surfaces. Boca Raton, FL: CRC Press, p. 94, 1993.