Rather than simply re-use Daniel Brassard’s topo pack, I took a quick stab at doing something myself (the only way to learn). Here, I try to implement the equations from wikipedia. Nothing fancy, I just add points to see if I’m getting it right.
I had to whip up some compounds for the hyperbolic functions cosh, sinh, and tanh.
eX-SI
ICE, scripting, and other tech stuff about Softimage aka XSI
eX-SI 
Thanks for this other solution, Stephen. I have linked your answer with the thread in si-community. If I may suggest, switch the y and z input into the Scalar to vector 3d node. That way the tight twist are at each pole.
Thanks Daniel, I’ll give that a try.
The hard part seems to be getting the right parameter values; hooking up a graph to match the equations seemed easy enough…
where do you get the Hyperbolic function component ?
Oh, I made those compounds myself based on what is on wikipedia.
https://dl.dropboxusercontent.com/u/12898205/cosh.xsicompound
https://dl.dropboxusercontent.com/u/12898205/sinh.xsicompound
https://dl.dropboxusercontent.com/u/12898205/tanh.xsicompound
Agreed. That is why I like ICE for parametric formula experimentation. The feedback is immediate and you can find some good parameters much faster than using a script.