* generate SEM data
clear
set obs 1000
gen x1 = rnormal(0,1)
gen e1 = rnormal(0,1)
gen e2 = rnormal(0,1)

local a0 = 1
local a1 = 2
local a2 = 3
local g0 = 4
local g1 = 5

local y1c = (1-`a1'*`g1')
local y2c = (1-`g1'*`a1')

gen y1 = (`a0' + `a1'*`g0' + `a1'*e2 + `a2'*x1 + e1)/`y1c'
gen y2 = (`g0' + `g1'*`a0' + `g1'*`a2'*x1 + `g1'*e1 + e2)/`y2c'

ivregress 2sls y2 (y1 = x1)