user defined functions

["H.C. Meyer at Triton" <hmeyer2 triton edu>]

The help files and documentation are silent on if, or how, I can define
my own functions for gnumeric.

I am using it to implement numerical solutions for differential
equations in connection with a class I am teaching. I have succeeded, by
defining and referencing additional columns for the terms of the Runge-
Kutta algorithm I am using, but it would be simpler if I could define
functions with one or more variables.

The whole idea is admittedly a travesty upon Applied Mathematics, but I
need a programming system that is accessible to the students. 

<middleAgedRant>
When I was in school, we all had time sharing accounts, and wrote
programs to do this. Now all you guys have computers, but I don't think
you can even spell Fortran, much less write programs in it.
</middleAgedRant>

Carl