Gompertz curve

[Han]

(03-30-2015 06:36 PM)salvomic Wrote:  However, about this curve I need help for the "inverse" problem: to use regression (interpolation) for that formula (Y=A*e^(-B*e^(-C*X))) with Statistic 2var (or otherwise).

I have a series of values for X (t, years) and Y (population):
X: 1,2,3,4,5,6,7,8,9
Y: 146583, 150203, 161475, 169182, 177619, 183054, 189431, 193082, 195687
I would get an estimation for A, B, C. (Then predict future values...)

I set in Symb -> Type: "User Defined" and Fit: "A*e^(-B*e^(-C*X))", but I'm not able to get plot and the values of estimated A, B, C, as I would like to have...
Any hints?

For this, you could create a system of equations resulting from substituting each pair of X and Y values into the general equation. Then use the generalized Newton's method to determine the least-squares fit. Snorre implemented such a function here:

http://www.hpmuseum.org/forum/thread-455.html#pid24491