Dear Stata experts,

I would like to do some postestimation analysis of an IV regression using coefficients from both the first and second stages. Here is an example of what I have in mind:

Code:
sysuse auto, clear
ivreg price turn (mpg = trunk)
nlcom _b[turn]*_b[trunk]
This does not work: "[trunk] not found". I tried using ivreg2 but without success. I'm using Stata/SE 14.2. Any help would be appreciated! Many thanks.