My regression analysis program that I developed in BASICS back in the 1980's applies for half a dozen equations. I would like to update my program to include this form: I(t)=P*(t^s)*(e^(-ft)) which I can transform it to this equivalent non- linear log form: Ln I(t)=Ln P + s*Ln t + (-ft); P,s and f are constants. Is there any way to take care of the term (-ft). I got 18 data points avaialble for this regression analysis.