drop _all
set seed 123456789
set obs 400
gen edu = invnorm(uniform())
gen exp = int(30*uniform())
label var exp "work experience"
gen inc = edu + log(0.1+10*exp) + 1*invnorm(uniform())
orthpoly exp, degree(3) gen(exp1 exp2 exp3)

regress inc edu exp exp2
graphf exp

regress inc edu exp exp2 exp3
graphf exp, cb(value)

mkspline Exp 4 = exp
regress inc edu Exp*
graphf exp, cb(envelop)

drop Exp*
gen Exp0 = (exp-15)^2
forv i = 1/3 { gen Exp`i' = max(0,exp-7.5*`i')^2 }
regress inc edu Exp*
graphf exp, cb(bs)