大神请指教：
已经构建了几何布朗运动的似然函数
如何用stata编写代码啊
doedit Homework_lf.ado
cap program drop Homework_lf
program define Homework-lf
        version 9.1
        args lnf mu sigma delta
        //(mu-0.5*sigma^2)^2*delta^2 均值
        //(sigma^2*delta)^0.5 方差
        quietly replace 'lnf'=ln(normalden(($ML_y1-'(mu-0.5*sigma^2)^2*delta^2')/'(sigma^2*delta)^0.5'))-ln('b')
end

sysuse auto, clear
gen cons = 1
ml model lf mymean_lf (Mean: price = cons) (Sigma: )
ml maximize
sum price

为什么显示：note: cons dropped because of collinearity和varlist not allowed