Software Citation for Gnumeric

["Gideon Butalid" <gbutalid gmail com>]

I am valuing the employee stock options of the company I am working in. I
use both the Generalized Black-Scholes and a particular Excel Addin for
customized binomial lattices. I specifically used R (fOptions package) and
Gnumeric (Black-Scholes function) to compute for a naive Black-Scholes
valuation.

I want to cite Gnumeric and the other software resources I used in the
formal document I am working on.

R provides the following citation: citation() in R prompt

  R Development Core Team (2006). R: A language and environment for
  statistical computing. R Foundation for Statistical Computing,
  Vienna, Austria. ISBN 3-900051-07-0, URL http://www.R-project.org.

Is there something similar for Gnumeric?
What is the proper way to cite Gnumeric as a software resource for a study
or analysis I am working on.

I tried to fill up the data above using info from the Gnumeric website, but
it's insufficient.

Thanks in advance.


-- 
Gideon