The umbilic torus appears in catastrophe theory in the context of classifying singularities. A clipping plan is included to demonstrate that the cross section is a deltoid curve.
This umbilic torus is defined parametrically by
x=[7+cos(u3−2v)+2cos(u3+v)]sinuy=[7+cos(u3−2v)+2cos(u3+v)]cosuz=sin(u3−2v)+2sin(u3+v)with −π≤u≤π and −π≤v≤π.
Complete code for this example: