On Jan 2 I posted a long discussion about fitting an exponential curve to data. It included this paragraph:
...... Of course the exponential regression is not fit to the actual data, but instead is a linear regression fit to (X,lnY) and then transformed back to exponential form. This technique does not minimize the sum of squares of the residuals, sum(Yi-A*B^Xi)^2 , but instead minimizes the sum of the residuals of the log of the data, i.e. it finds a and b that minimizes <<sum(lnYi-a-blnXi)^2>>. Then it calculates A=e^a and B=e^b for the equation Y=A*B^X. .........
There is a mistake above. The bit inside the << >> should read sum(Yi-a-bXi)^2. That is, you don't take the ln of the Xi's when fitting an exponential curve. Sorry about that. It doesn't affect the rest of the discussion.
-- Doug Kuhlmann (508)-749-4242 Phillips Academy firstname.lastname@example.org Andover, MA 01810