gear iterators



I want to model reaction rate constants where all four compunds A,B,C and D are interconvertble and where an equilibrium is eventually established.
 
I have searched the literature and found that the use of an algorythm known as GEAR iteration will do the job provided that the concentrations of all 4 components versus time are known.
 
If anyone knows where I can obtain software of GEAR Iterators (prefereably freeware) it will be most appreciated.
 
Marcelo Sales
Dept of Chemistry
University of Saskatchewan
sales -AatT- duke.usask.ca