i_nfunc Library part 2© Mike Williams 2001,2002,2003,2004 

This is the f_spikes_2d surface.
The parameters are:
f_spikes_2d(x,y,z,0.4,15,15,2.5)  
There's a comment in the source code that says "well known
function in quantum mechanics". I don't know quantum mechanics
well enough to recognise it.
The parameters are:
f_quantum(x,y,z,0)  
This is the f_helical_torus surface. With some sets of parameters, it looks like a
helix bent into a circle with, optionally, a torus through the middle.
The helix optionally has grooves around the outside. I'm not completely sure about how the parameters work for this surface. The parameters are something like:
function {f_helical_torus (x,y,z, 6, 12, 2, 0.1, .5, 1, 0.1, 1, 1.0, 0)} function {f_helical_torus (x,y,z,2, 5, 1, 0.1, 1, 0.5, 1, 6, 3, 0)}A more controlable helical torus can be created by starting with an ordinary helix and then transforming the coordinate system from cartesian to cylindrical polar coordinates.  
The f_comma surface is very much like half a Yin/Yang. I've included two of them in the image, and chosen the viewing angle so that you can't see that they don't quite fit together properly in the middle. Actually, they fit reasonably well if you set the threshold to about 0.05. The parameters are:
function {f_comma(x,y,z,1)  
The f_polytubes surface consists of a number of tubes. Each tube follows a 2d curve which
is specified by a polynomial of degree 4 or less.
The parameters are:
function {f_polytubes(x,y,z,4,0,1,0,1,0)}  

Download a zip file containing the POV source files for all the images that appear on this page. 
