04-18-2018 06:55 AM - edited 04-18-2018 09:26 AM
I am trying to fit a logistic price demand curve like so:
ods select none; proc nlmixed data=TrainingData; bounds L > 100, Sd1 > 0, Parameter1 > 0, k > 0, var2 >= 0; parms L = 101, Sd1 = 0.5, Intercept = 1.0, Parameter1 = 0.001, k = 2, pa1=18, b1 =0; Parameter1 = pa1 + b1; Y = L / -k * exp(Intercept + Parameter1 * Price); model Demand ~ normal(Y, Sd1); random b1 ~ normal(0, var2) subject = ProductId; ods output Parameters = Parameters FitStatistics = ModelFit ; run; ods select all;
This code is just a starting point! I played around with some parameters in Excel and found some OK-ish ones, which I provided as starting parameters. Unfortunately, the algorithm does not change the provided parameters when I inspect dataset Parameters (created using Parameters = Parameters). I doubt I chose the optimal parameters - so I would expect the parameters in the dataset Parameters to be adjusted. Is there something wrong with the above, which prevents the parameters from being changed? Thanks!
04-18-2018 07:39 AM
Unfortunately, the algorithm does not change the provided parameters when I inspect dataset Parameters.
I'm not really sure what you mean by this. I'm not sure what you mean when you say "I Inspect dataset parameters". Could you be much more specific?
It is possible the algorithm can't iterate from this starting position, and so the parameters don't change.
04-18-2018 09:29 AM