The surface which is the inverse of the Ellipsoid in the sense that it ``goes in'' where the Ellipsoid ``goes
out.'' It is given by the parametric equations
See also Ellipsoid, Hyperbolic Octahedron
References
Nordstrand, T. ``Astroidal Ellipsoid.''
http://www.uib.no/people/nfytn/asttxt.htm.