program define tryls
    version 4.0

    preserve 
    clear

    set obs 20
    gen x=invnorm(uniform())
    gen y=invnorm(uniform())
    local int=0
    local slope=1
    lsfit x y 

    di $slope
    di $int

    regress y x

    restore

end

program define lsfit
    version 4.0

    local x     = "`1'"
    local y     = "`2'"

    tempvar z

    qui summarize `x'
    local xbar=_result(3)
    local sxx =_result(4)*(_N-1)
    di `xbar'
    qui summarize `y'
    local ybar=_result(3)

    gen `z'=(`x'-`xbar')*(`y'-`ybar')
    replace `z'=sum(`z')
    local sxy=`z'[_N]

    global slope = `sxy'/`sxx'
    global int   = `ybar'-$slope*`xbar'

end
exit