给一个tobit的例子
set more off

*******************************************************************************************************

capt prog drop myprobit_if
prog myprobit_if

          args lnf xb
          quietly replace `lnf' = ln(exp(`xb')/(1+exp(`xb'))) if $ML_y1==1
          quietly replace `lnf' = ln(exp(-`xb')/(1+exp(-`xb'))) if $ML_y1==0

end

*******************************************************************************************************

sysuse cancer,clear

gen drug2=drug==2

gen drug3=drug==3

ml model lf myprobit_if (died=drug2 drug3 age)

ml maximize