How to perform NLS estimation with a complex function

[Melissa Moular]

Dear Stata users,


I need to use NLS to estimate the following equation describing the so-called Bass diffusion model:

y_t = m * [ ((1 - exp (-(p+q) * t)) / (1 + q/p * exp (-(p+q) * t))) - ((1 - exp (-(p+q) * (t-1))) / (1 + q/p * exp (-(p+q) * (t-1)))) ] + u_t

where m,p, and q are parameters and t indicates time. As initial values for these parameters, I am to use those obtained with OLS applied to:

y_t = β₀ + β₁ x_{1, t-1} + β₂ x_{2, t-1} + ϵ_t

where β₀ = m * p
β₁ = q - p
β₂= - q/m

Note that m = 41302528
p = 0.024
q = 0.194


To perform this NLS estimation, I tried to follow the example that was given in the Stata forum (https://www.stata.com/features/overv...ar-regression/) in order to create a program that defines my function.Then, I used the nl command and specified the initial values.

When I run the command, I get the following message:

verify that nlces is a function evaluator program
r(198);

Would you please help me figure out what the problem is? I am a beginner in Stata software.
Thanks in advance.

[William Lisowski]

This is also posted in the more appropriate location of the General Forum (rather than the Mata Forum) at

https://www.statalist.org/forums/for...mplex-function

with subsequent follow-up.