afni.nimh.nih.gov

Hi AFNI gurus
Can someone let me know the details of the algorithm used to fit the auto-correlation function in 3dFWHMx?
Specifically how was the equation ACF(r) = a * exp(-r*r/(2*b*b)) + (1-a)*exp(-r/c) fitted?
Did you use some kind of a non-linear data fitting algorithm? What were the upper and and lower bounds allowed on the ACF parameters "a", "b" and "c" ?

Thanks a million
Gopi